Low RPMs bucking

[MuRCieLaGo]

Hi,

'91 ZR-1.

Valet key always ON.

I'm getting severe buckings at WOT when I'm under 3,500 RPM. High RPM is fine, pulls strong.

For 3 or 4 miles this morning the car felt like it was running on 7 cylinders, from 1,000 RPM to 7,000 RPM. I took a 400 miles ride and it never happened again. Fuel consumption was good.

However, the low RPMs bucking is still happening. It's been like this since I bought the car 3,000 miles ago. Warm or not.

New from this year though: sometimes, the RPM needle would jump from 4,000 RPM to 1,000 RPM suddenly only for a moment (total power loss), then immediately comes back to 4,000 RPM. Happens especially when the car isn't fully warmed up yet.

No SES light.

I electrically tested the injectors last fall and everything was perfect.

You guys got an idea? Is it normal to get bucking at low RPMs?

[Billy Mild]

Have you done a tuneup or changed O2 sensors?

[MuRCieLaGo]

I recently changed the headers and added a o2 sensor 2 feet extension on passenger side. I also had Marc Haibeck burn me a chip.

[Billy Mild]

The bucking has not changed at all?

I would at least throw a set of new spark plugs in it. If that doesn't help then start looking at coils and wires. I have a similar issue except my car isn't always noticeable.

[A26B]

1. Sounds like a closed loop issue
2. You recently altered O2 sensor wiring
3. Bucking you describe can be directly associated with a single bank, shorted O2 sensor
4. Shorted O2 sensor symptoms will disappear in open loop, i.e. above 3200rpm

Recommend you check there first. Verify extension is properly wired, & make sure the connections are dry inside, no moisture. Do not tie back the extension underneath the AC condensate drain. Ask me how I know :-)

[MuRCieLaGo]

The bucking has not changed at all?

I would at least throw a set of new spark plugs in it. If that doesn't help then start looking at coils and wires. I have a similar issue except my car isn't always noticeable.

Just ordered a 5/8'' socket with a swivel to change the plugs!

1. Sounds like a closed loop issue
2. You recently altered O2 sensor wiring
3. Bucking you describe can be directly associated with a single bank, shorted O2 sensor
4. Shorted O2 sensor symptoms will disappear in open loop, i.e. above 3200rpm

Recommend you check there first. Verify extension is properly wired, & make sure the connections are dry inside, no moisture. Do not tie back the extension underneath the AC condensate drain. Ask me how I know :-)

I'm a bit surprised by what you are saying there. I hope there's a way to test the sensors without having to remove them from the headers... I'm pretty sure the wiring is fine...

Like I said, no SES light. I check the codes even if I don't have a SES light and no code is stored.

[XfireZ51]

Keep your foot in it and continue the bucking. See if it sets a code. You may see a Code 61 and a Code 44. The bucking may be due to a bad fuel pump.

[LGAFF]

check both map sensor hoses

[MuRCieLaGo]

Keep your foot in it and continue the bucking. See if it sets a code. You may see a Code 61 and a Code 44. The bucking may be due to a bad fuel pump.

I already tried this and never saw any SES light... The fuel pump would be a good guess though, previous owner told me some water went in the fuel tank and it froze. I tested the pump last fall and the resistance was a bit too high...

check both map sensor hoses

Both? There's only one hose there...

[LGAFF]

one under the ecm

[MuRCieLaGo]

one under the ecm

Oh! Yes it's plugged in!

[WVZR-1]

You've much to consider and it's been since "day one" so ... a pair of pumps, then there's that what's thought to be repaired ECM pin. What terminal on which connector did that turn out to be? I believe there were three possibilities.

[MuRCieLaGo]

You've much to consider and it's been since "day one" so ... a pair of pumps, then there's that what's thought to be repaired ECM pin. What terminal on which connector did that turn out to be? I believe there were three possibilities.

-Repaired ECM pin: can't tell you which terminal. When it was unpinned, the car ran like total crap. It was a ground. But like I said, the shop who repaired it is serious and they have a strong reputation, including from myself in the past.

-Pair of pumps: how do you test the pressure?

-Spark plugs: ordered some new plugs, will be receiving them shortly.

-o2 sensor: I'd like to find a way to test them without having to remove them.

-Coil pack/spark plug wires: not sure how to do this, but there must be a way to test them.



Worst than ever today.

Just before it gets fully warmed up, the car pulled OK. Then, it ran like crap again.

I joined a video, in which we don't really see the misfires, but we can feel the sudden power loss.

https://www.youtube.com/watch?v=cQb882XCwK8

For what it's worth, I'm changing the fuel filter tomorrow.

Should I ask a local tuning shop to run the car on a dyno to help me with the problem?

[A26B]

Just before it gets fully warmed up, the car pulled OK. Then, it ran like crap again.

Before it warms up, it's running in open loop. Switches to closed loop after warmed up.

In open loop;
(1) both primary & secondary fuel pumps are operating,
(2) O2 sensor input is not used.

Obviously NOT fuel filter, coils, plugs or plug wires if it runs fine in open loop.

May be primary fuel pump or O2 sensor.

You do not need to dyno, only data log & look at O2 counts. You should also do a static fuel pressure test & isolated each pump to verify pressure output & leakdown.

[MuRCieLaGo]

Before it warms up, it's running in open loop. Switches to closed loop after warmed up.

In open loop;
(1) both primary & secondary fuel pumps are operating,
(2) O2 sensor input is not used.

Obviously NOT fuel filter, coils, plugs or plug wires if it runs fine in open loop.

May be primary fuel pump or O2 sensor.

You do not need to dyno, only data log & look at O2 counts. You should also do a static fuel pressure test & isolated each pump to verify pressure output & leakdown.

Last fall, I had similar bucking problems, only when the Valet key was turned off.

I got no idea how to data log this... And I'd love to know how to run a fuel pressure test!

But if it runs fine in open loop as you suggest, can't we eliminate the primary fuel pump theory? I'll let the car cool down again and I'll go for a ride tonight, to confirm it runs fine in open loop.

Thanks a lot for your help!

[A26B]

You cannot eliminate the primary fuel pump in open loop operation. Both the Primary & Secondary fuel pumps will run in open loop, masking a problem with one fuel pump. In open loop, the Secondary fuel pump may be the only pump operating to spec. Accordingly, when the engine warms to operating temp & goes into closed loop, the Secondary is on standby & not running. Only the Primary fuel pump runs in closed loop, which is when your problem occurs, hence the need to isolate & check each fuel pump, particularly the Primary.

The procedure for performing a static fuel pump test has been discussed many times & should be easily found searching the archives. I'll wager Dynomite has is tagged in Solutions

[MuRCieLaGo]

You cannot eliminate the primary fuel pump in open loop operation. Both the Primary & Secondary fuel pumps will run in open loop, masking a problem with one fuel pump. In open loop, the Secondary fuel pump may be the only pump operating to spec. Accordingly, when the engine warms to operating temp & goes into closed loop, the Secondary is on standby & not running. Only the Primary fuel pump runs in closed loop, which is when your problem occurs, hence the need to isolate & check each fuel pump, particularly the Primary.

The procedure for performing a static fuel pump test has been discussed many times & should be easily found searching the archives. I'll wager Dynomite has is tagged in Solutions

Thanks a lot for your explanations! I'll concentrate my efforts in testing the fuel pumps now. Performing a fuel pump test seems to be quite easy, except that I'm not sure where to plug the "T"!

I just took the car for a ride (wasn't fully cooled down) and it's running way better, without any reason. I had it reach operating temperature and it's still running strong.

I just don't get it.

https://www.youtube.com/watch?v=dMGc9vCqdoM

[A26B]

Here's an old post for pump testing.

There are 2 fuel pumps, FP1 is the primary and FP2 is the secondary pump. For a cold start, both FP1 & FP2 will run until the engine reaches appx 176F, then FP2 will shut off. For a hot start, above 176F, both FP1 & FP2 will run, but after 2 sec, FP2 will shut off.

To determine the functionality of the pumps, they must be tested separately. There are 2 fuses. FP1 fuse is on the pass side of the dash in the fuse panel. The fuse is labeled FP1. FP2 fuse is under the passenger side dash kick panel. Remove the panel. The fuse is labeled FP2.

The procedure to check fuel pumps is as follows;

Cold Engine
Key off, Engine off
Attach Fuel pressure gauge line to fuel rail. Bleed down any pressure in the rail.

Testing FP1 (Primary Fuel Pump)

1. Remove FP2 fuse.

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

Testing FP2 (Secondary Fuel Pump)

1. Replace FP2 fuse and remove FP1 fuse

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

6. Replace FP1 fuse.

[MuRCieLaGo]

Here's an old post for pump testing.

There are 2 fuel pumps, FP1 is the primary and FP2 is the secondary pump. For a cold start, both FP1 & FP2 will run until the engine reaches appx 176F, then FP2 will shut off. For a hot start, above 176F, both FP1 & FP2 will run, but after 2 sec, FP2 will shut off.

To determine the functionality of the pumps, they must be tested separately. There are 2 fuses. FP1 fuse is on the pass side of the dash in the fuse panel. The fuse is labeled FP1. FP2 fuse is under the passenger side dash kick panel. Remove the panel. The fuse is labeled FP2.

The procedure to check fuel pumps is as follows;

Cold Engine
Key off, Engine off
Attach Fuel pressure gauge line to fuel rail. Bleed down any pressure in the rail.

Testing FP1 (Primary Fuel Pump)

1. Remove FP2 fuse.

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

Testing FP2 (Secondary Fuel Pump)

1. Replace FP2 fuse and remove FP1 fuse

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

6. Replace FP1 fuse.

Seems to be quite easy, except for that "Attach Fuel pressure gauge line to fuel rail." part. Pretty sure I'll have to remove the plenum, isn't there a way to attach it in the tank?

Thank you very much Jerry, I really appreciate that!

[secondchance]

Seems to be quite easy, except for that "Attach Fuel pressure gauge line to fuel rail." part. Pretty sure I'll have to remove the plenum, isn't there a way to attach it in the tank?

Thank you very much Jerry, I really appreciate that!

You do not have to remove plenum to attach fuel pressure gauge. Front of fuel rail on the passenger side has a Schrader valve readily accessible. There is an aluminum cap similar to tire valve stem cap.

[MuRCieLaGo]

You do not have to remove plenum to attach fuel pressure gauge. Front of fuel rail on the passenger side has a Schrader valve readily accessible. There is an aluminum cap similar to tire valve stem cap.

Alright thank you!

[MuRCieLaGo]

Update:

Changed fuel filter today.

Finally got a SES code, 64: Right Oxygen Sensor Circuit Lean. The SES code switches the engine back to 16 valves, right? It runs so smooth when the SES light is on, except at idle. It makes some sounds that I REALLY don't like. The noise stops when I give some gas.

https://www.youtube.com/watch?v=CsC2Z3JdEDU

I tried to get a fuel pressure gauge locally. Can't find any, I'll have to order one.

What do you guys think about this now? Please, don't stress me more than I am at the moment.

EDIT: I just started the car 5 minutes later and no more knocking sound, but god I don't like that.
EDIT #2: YES I still got the knocking sound...

[RussMcB]

That knocking noise happened to me once and it was scary but I learned here that it is a temporary lifter noise (hydraulic lifters not pumping up for some reason). It went away on its own in a short time. Hopefully yours is the same.

[MuRCieLaGo]

That knocking noise happened to me once and it was scary but I learned here that it is a temporary lifter noise (hydraulic lifters not pumping up for some reason). It went away on its own in a short time. Hopefully yours is the same.

Glad to read this! Like I wrote, I started the car 5 minutes later and it was gone.

I hope the reliability of this legendary engine will deliver soon, because at the moment I'm not impressed.

[RussMcB]

Hopefully you'll get the bugs worked out and have years of enjoyment from it. You haven't had it long, right? When I bought mine 1/1/2015 it ran horribly but coils/injectors fixed it mostly. I also found that my stock exhaust must've had problems because I went from an under-powered ZR-1 to a healthy, strong runner with an exhaust change. I still have more to address but I thoroughly enjoy my car now, especially pushing it hard on track days. It handles the hard use with ease, so it's robust, for sure. So, have patience (I know that's easier to say than do), methodically tackle issues and it should be great again in due time.

[MuRCieLaGo]

Alright.

Still having that knocking sound problem. Oil level is OK, 5w30 High Mileage Mobil1.

Fuel pressure is OK on both pumps.

Idle: 41 psi.
FP1: 46 psi.
FP2: 48 psi.

[MuRCieLaGo]

Panic mode is now enabled.

I ran the engine and removed each spark plug wire, one by one, to see if the knocking stops. It gets worst each time I remove a wire, on every single wire. I think it eliminates the rod knocking theory?

I'm sorry, I'm used to rotary engines. I'm only beginning with piston engines. Supposed to be easier but I doubt it.

Please help me...

[secondchance]

Panic mode is now enabled.

I ran the engine and removed each spark plug wire, one by one, to see if the knocking stops. It gets worst each time I remove a wire, on every single wire. I think it eliminates the rod knocking theory?

I'm sorry, I'm used to rotary engines. I'm only beginning with piston engines. Supposed to be easier but I doubt it.

Please help me...

Where the tensioner pulley is squeezing the drive belt, how much gap to the belt running between the water pump pulley to alternator? If the gap is too narrow, your belt may be too long allowing the tensioner to bottom out. When this happens stops on the bottom of the tensioner fixed portion and the pivot will tap each other. I chased this noise for 3-4 months.

[MuRCieLaGo]

Where the tensioner pulley is squeezing the drive belt, how much gap to the belt running between the water pump pulley to alternator? If the gap is too narrow, your belt may be too long allowing the tensioner to bottom out. When this happens stops on the bottom of the tensioner fixed portion and the pivot will tap each other. I chased this noise for 3-4 months.

Funny you mention the tensioner pulley, I took a video of it yesterday afternoon. I noticed it's loose. There's definitely a problem there, but I don't think it's related to my current issues.

It was already loose and it didn't have that scary noise...

https://www.youtube.com/watch?v=MpjCBBhHJhw

[MuRCieLaGo]

May I add that the knocking sound is irregular? Sometimes the knocking sound happens twice a second, then nothing for the next 3 seconds...

[MuRCieLaGo]

No unusual oil consumption, oil pressure is also good.

New code showed up today.

Code #55: System Voltage.

When I first went to buy the car, the previous owner told me to come back because the alternator was broken, so he can put a brand new alternator.

Since I got this car, at night, I can see the dash lighting isn't stable at all. But, like I just told you, the alternator is brand new.

And at idle it does seem it "wants" to die (idle at about 600 RPM, which is a bit low).

[MuRCieLaGo]

Wait, is there a mistake? At some places it says that code #55 is System voltage and some other places it says Fuel lean monitor...

I'm not sure if I already mentionned it, but previous owner told me the injectors were brand new (and I know he's honest).

[LGAFF]

battery terminals tight?

Alternators can fail even when new....whats the voltage its producing?

[secondchance]

Wait, is there a mistake? At some places it says that code #55 is System voltage and some other places it says Fuel lean monitor...

I'm not sure if I already mentionned it, but previous owner told me the injectors were brand new (and I know he's honest).

I believe DTC 55 is "fuel monitor lean". I would start with fuel pressure - fuel pumps followed by injectors. Not too many sellers are eager to replace injectors because typical dealer charge to replace 16 injectors is $3,500 to 4,000. Not saying previous owner did not replace them. Just don't assume they were replaced.

[MuRCieLaGo]

battery terminals tight?

Alternators can fail even when new....whats the voltage its producing?

Terminals are tight.

Just hooked a multimeter to the battery terminals:

OFF: 12.4V
Idle: 14.3V (constant between 14.32V and 14.36V)

I believe DTC 55 is "fuel monitor lean". I would start with fuel pressure - fuel pumps followed by injectors. Not too many sellers are eager to replace injectors because typical dealer charge to replace 16 injectors is $3,500 to 4,000. Not saying previous owner did not replace them. Just don't assume they were replaced.

I also spoke to his mechanic (well-known Corvette mechanic in the Canadian Atlantic area) and he told me in a direct way they were changed, but yeah anybody could lie...

I already tested the fuel pressure yesterday:

Idle: 41 psi
FP1: 46 psi
FP2: 48 psi

I'm officially not running this car anymore now, until it gets fixed.

[RussMcB]

Are there any other ZR-1's near you? If yes, maybe you could borrow their ECU briefly to see if it makes a difference. My ECU has been in two other cars and that helped them narrow down the possible cause for their rough-running conditions.

Kind of shocking a dealer would charge $3,500-$4,000 to change injectors, but, then again, maybe not that shocking.

[LGAFF]

fuel pumps replaced? possible the clips/clamps for the lines are loose and bleeding pressure?

[Paul Workman]

Well, I gotta give you credit...you are tenacious! However, some things are obvious that are giving you a lot of frustration too. And, too I think most would agree that you have touched on the problem, or been close, but just didn't realize it. AND, too, you've gotten off on some tangents which is "muddying the waters" a bit... But! I can tell that once you become fully acquainted, you'll soon be answering questions for others! Don't get discouraged.[-X Hang in there! :dancing

First off, it appears you have at least 2 (if not more) issues going on:

ONE being a CLOSED LOOP issue (as Jerry pointed out)

TWO, a wiring issue - probable grounding (more common)

The 4 RULES OF TROUBLESHOOTING


Know how the system works
Assume NOTHING! Measure and document
One issue at a time!
Divide and eliminate.


Knowing how the system works: These motors are NOT complicated, BUT the control/monitoring systems are specific and unique (e.g., open vs. closed loop operation) to the point that troubleshooting effectively w/o getting distracted really (almost) mandates one read the FSM from cover to cover. Doing so will provide an overview of the nuances, but also provides prepared troubleshooting guides and how to test stuff, etc. So, my first question is: Do you have an FSM??


Assume nothing...NOTHING! AND, measure! In that regard, you've touched on some pretty good indicators that at least narrows the problem(s) down considerably. And, too, it appears (to me) there my well be at least two different issues: closed loop issue, and an electrical malady.

One issue at a time: The "BUCKING" issue is the highest priority (now). (Note: Sometimes two or more issues have commonality - especially electrical, but it is best to stay focused and work the issues individually. (Otherwise, it can easily get confusing and contradictory...did I mention frustrating?)

Hear is a summary of what you've tested or experienced (or attempted to test)*:


"Bucking" at <3000 rpm AND especially after it warms up (but not before)
The tach reading is erratic at times
NO SES light
Injectors "tested" ***
Haibeck chip installed
O2 wiring added on passenger side
O2s NOT checked
MAP connections "OK"
ECM connector repaired (!)
New fuel filter
knocking sound at idle, and low idle speed (600 rpm)
Belt tensioner checked
Dash lights flicker some


Divide and eliminate! This problem is really in two (?) parts. With knowing how the system works, symptoms and measurement data too can be grouped separately and then prioritized. In this case, those items that are related to the rough running, primarily in "closed loop" and NOT at WOT points to closed loop components; i.e., injectors, fuel pressure, MAP sensor, O2 sensors, Throttle Position Switch (aka TPS), and ECM.

As mentioned, checking for codes is always a good way to gather a lot of information. HOWEVER, often old codes that are no longer applicable linger in the memory. Disconnecting the power to the ECM for a minute or so will clear the memory. Sometimes codes are stored that no longer apply which can send us in the wrong directions. But, also some problems are not instantly recorded/stored: erasing them could remove important clues. So, to play it safe, it is a good thing to note what problems are stored before clearing the ECM to "clean the slate". Clearing is a good tool, but it is tricky. (And, sometimes a code is set that does not appear to be directly associated with the actual fault. This happens especially if the fault effects more than one sensor, e.g., injectors.)

Rough idle and or a [I]knocking sound (dual mass FW**), low rpm, stalling, running OK when cold, but rough when it warms up, running OK with rpm and/or moderate to heavy throttle (esp. WOT) are classic fuel delivery issues at CLOSED LOOP ONLY.

**If the knocking sound goes away when you depress the clutch pedal, it is probably the result of rough idle pulses which usually causes a knocking sound from the dual mass flywheel. This is but one of the tell-tale signs of a bad injector or an O2 sensor issue.

Running strong at (OPEN LOOP) tends to eliminate fuel delivery pretty much in your case. However, just for the record (FYI) a dynamic fuel test will expose weak pumps or plugged in-line filter (you DO know there is an in-line filter (located just behind the front passenger wheel housing), yes?

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/FPtestLarge.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/FPtestLarge.jpg.html)

In closed loop conditions, and fully warmed up, the dynamic pressure will be around 42-45 psi. in open loop conditions the combined fuel pressure will be 52-55 psi.

Injectors: My injectors had just been replaced when I bought my 90 Z. At issue was they were replaced with NOS, and they too went bad due to alcohol exposure! SO! Unless you've checked resistance when the motor is fully warmed up, you can't be sure they are good. Typically the shellac-insulaiton on coils fails, it goes undetected until the coil is heated. There are a couple ways to take the resistance readings. How and under what teperature conditions did you test yours, may I ask?

Throttle Position Switch: Sometimes the TPS wiper is dirty or has failed. This too is FYI, and not related to closed loop per se'. By disconnecting the electrical plug you can operate the TPS through its enter throttle range while watching the (analog) resistance indicator on the VOM, looking for a smooth change in resistance through the entire range.

With the connector reassembled and the ignition switch to ON, motor OFF, the TB wiper should be set to 5.5 VDC.

O2 sensors:

The O2 sensor operation (including 'cross counts') can easily be monitored with a dynamic scan (most auto parts stores have that capability). And, also, the sensor can be removed and tested with a VOM and a propane torch.

https://axleaddict.com/auto-repair/How-to-Check-an-Oxygen-Sensor

A lazy (low # of cross-counts) or non-responding O2 sensor, especially an intermittently failing one can result in a number of closed loop symptoms (but not exclusive of closed loop operation either!) - especially idle irregularities and rough running, fouled plugs (on one bake only...is important to note) are some of the more common issues.

Not because of your symptoms in particular, but more of an FYI, you asked about checking the coils.

Well, the acid test for ignition is proper operation at WOT when the motor is fully warmed up! Furthermore, a pin-hole can develop in a wiring insulation that cannot be detected with a standard VOM: a MEGGAR or dedicated test equipment is required, which is uncommon except in the better repair shops.

The LT5 uses a "waste spark" design. Each coil fires two plugs at the same time.

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Ignitioncircuit-LT5.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Ignitioncircuit-LT5.jpg.html)

That said, the resistance can be measured across the spark terminals and compared with the readings across all 4 coils. (But, again, not all coils e.g., AC/Delco, MDS, Excel, etc. read the same, specifically, and may vary from type to type!) Plug wires resistance values vary too, depending on the make/type. However, the resistance should be proportional to their length; i.e., a wire twice as long as another should have close to twice as much resistance as the shorter one.


Well... w/o more specific info, this could get very superfluous (if not already!). So, I'll stop till I hear more specifics from you first.

:cheers:

[LGAFF]

fuel filter backwards?

[MuRCieLaGo]

Are there any other ZR-1's near you? If yes, maybe you could borrow their ECU briefly to see if it makes a difference. My ECU has been in two other cars and that helped them narrow down the possible cause for their rough-running conditions.

Kind of shocking a dealer would charge $3,500-$4,000 to change injectors, but, then again, maybe not that shocking.

Nearest ZR-1 that I "know" of is 5ABI VT's and he lives about 700 miles from me.

fuel pumps replaced? possible the clips/clamps for the lines are loose and bleeding pressure?

The pumps have not been replaced. I'll remove them today and do a visual inspection.


Well, I gotta give you credit...you are tenacious! However, some things are obvious that are giving you a lot of frustration too. And, too I think most would agree that you have touched on the problem, or been close, but just didn't realize it. AND, too, you've gotten off on some tangents which is "muddying the waters" a bit... But! I can tell that once you become fully acquainted, you'll soon be answering questions for others! Don't get discouraged.[-X Hang in there! :dancing

First off, it appears you have at least 2 (if not more) issues going on:

ONE being a CLOSED LOOP issue (as Jerry pointed out)

TWO, a wiring issue - probable grounding (more common)

The 4 RULES OF TROUBLESHOOTING


Know how the system works
Assume NOTHING! Measure and document
One issue at a time!
Divide and eliminate.


Knowing how the system works: These motors are NOT complicated, BUT the control/monitoring systems are specific and unique (e.g., open vs. closed loop operation) to the point that troubleshooting effectively w/o getting distracted really (almost) mandates one read the FSM from cover to cover. Doing so will provide an overview of the nuances, but also provides prepared troubleshooting guides and how to test stuff, etc. So, my first question is: Do you have an FSM??


Assume nothing...NOTHING! AND, measure! In that regard, you've touched on some pretty good indicators that at least narrows the problem(s) down considerably. And, too, it appears (to me) there my well be at least two different issues: closed loop issue, and an electrical malady.

One issue at a time: The "BUCKING" issue is the highest priority (now). (Note: Sometimes two or more issues have commonality - especially electrical, but it is best to stay focused and work the issues individually. (Otherwise, it can easily get confusing and contradictory...did I mention frustrating?)

Hear is a summary of what you've tested or experienced (or attempted to test)*:


"Bucking" at <3000 rpm AND especially after it warms up (but not before)
The tach reading is erratic at times
NO SES light
Injectors "tested" ***
Haibeck chip installed
O2 wiring added on passenger side
O2s NOT checked
MAP connections "OK"
ECM connector repaired (!)
New fuel filter
knocking sound at idle, and low idle speed (600 rpm)
Belt tensioner checked
Dash lights flicker some


Divide and eliminate! This problem is really in two (?) parts. With knowing how the system works, symptoms and measurement data too can be grouped separately and then prioritized. In this case, those items that are related to the rough running, primarily in "closed loop" and NOT at WOT points to closed loop components; i.e., injectors, fuel pressure, MAP sensor, O2 sensors, Throttle Position Switch (aka TPS), and ECM.

As mentioned, checking for codes is always a good way to gather a lot of information. HOWEVER, often old codes that are no longer applicable linger in the memory. Disconnecting the power to the ECM for a minute or so will clear the memory. Sometimes codes are stored that no longer apply which can send us in the wrong directions. But, also some problems are not instantly recorded/stored: erasing them could remove important clues. So, to play it safe, it is a good thing to note what problems are stored before clearing the ECM to "clean the slate". Clearing is a good tool, but it is tricky. (And, sometimes a code is set that does not appear to be directly associated with the actual fault. This happens especially if the fault effects more than one sensor, e.g., injectors.)

>>> gotta run just now, but I'll finish this later!













>>O2 sensor(s) not checked!
>>TPS voltage?
>>How to check coils

First of all thank you very much Paul for this detailed answer. I'm used to problems (I'm owning a car with a rotary engine since 2007). I hope my knowledge of the LT5 will be soon as strong as the rotary engines.

I got the FSM, but I don't think I'm ready to read it from cover to cover. Maybe that would help me troubleshoot the problem though.

Useful summary with some corrections:

1. "Bucking" at <3000 rpm AND especially after it warms up (but not before)
2. The tach reading is erratic at times
3. NO SES light Yes, code 55 and code 64. They appeared some miles after I installed the new fuel filter (as well as the knocking noise). I think this is a pure coincidence though.
4. Injectors "tested" *** Last fall, electrically tested
5. Haibeck chip installed
6. O2 wiring added on passenger side
7. O2s NOT checked
8. MAP connections "OK"
9. ECM connector repaired (!)
10. New fuel filter
11. knocking sound at idle, and low idle speed (600 rpm) And my primary concern now! Scary stuff!
12. Belt tensioner checked And loose
13. Dash lights flicker some

The codes 55 and 64 aren't old codes. I plugged my ALDL Code Reader 4 days ago (even if I had no SES light) and no code was stored. SES light came on 2 days ago, code 64 showed up. Then, yesterday, after a 60 miles WOT pull, code 55 also showed up.

I've ran with blown o2 sensors in a lot of cars. You really think this could be a problem on a ZR-1?

fuel filter backwards?

I installed a WIX fuel filter. On it, there was a tiny black arrow --->.

Fuel pumps ---> Fuel rail.
Rear ---> Front.

That's how I installed it.

[MuRCieLaGo]

Update:

Removed fuel pumps assembly and visually inspected it. Everything seems to be fine.

Went under the car to double-check the fuel filter (without success), I found something interesting instead.

https://www.youtube.com/watch?v=fHqLdS43baU

One of the wire in the o2 sensor connector is loose, as you can see in the video. I'm going to fix it tomorrow morning (will replace the connector). It is the passenger side o2 sensor, it probably explains why I got code 64 showing up (and why I had the code only since I replaced the fuel filter. The connector is fixed to the fuel line... I probably broke it while working on the fuel filter).

But I'm still scared about the knocking noise.

Started the car this morning to park it in and out of the garage and I didn't hear the noise, but it is still a concern.

[geezer]

Monitoring your situation & progress/ frustration! I'm closer than T.O. being in Ottawa area so if I can help in anyway.

[MuRCieLaGo]

Monitoring your situation & progress/ frustration! I'm closer than T.O. being in Ottawa area so if I can help in anyway.

Good to know thanks for your support! I'm still 450 miles from Ottawa...

[Paul Workman]

I'm back. See additional info on my earlier post.

[Bruce]

I just logged into this forum. After reading the site for the last year Ive just joined.

Ok, the knocking sound you have is the clutch unit on the AC compressor. Not a biggie, its just rattling around as you will see if you get closer and have a look. Thats why the sound will come and go. I had the same thing on mine, and I just replaced the clutch unit and its sweet as now.

[MuRCieLaGo]

[...]Rough idle and or a knocking sound (dual mass FW**), low rpm, stalling, running OK when cold, but rough when it warms up, running OK with rpm and/or moderate to heavy throttle (esp. WOT) are classic fuel delivery issues at CLOSED LOOP ONLY.

**If the knocking sound goes away when you depress the clutch pedal, it is probably the result of rough idle pulses which usually causes a knocking sound from the dual mass flywheel. This is but one of the tell-tale signs of a bad injector or an O2 sensor issue.

Running strong at (OPEN LOOP) tends to eliminate fuel delivery pretty much in your case. However, just for the record (FYI) a dynamic fuel test will expose weak pumps or plugged in-line filter (you DO know there is an in-line filter (located just behind the front passenger wheel housing), yes?

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/FPtestLarge.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/FPtestLarge.jpg.html)

In closed loop conditions, and fully warmed up, the dynamic pressure will be around 42-45 psi. in open loop conditions the combined fuel pressure will be 52-55 psi.

Injectors: My injectors had just been replaced when I bought my 90 Z. At issue was they were replaced with NOS, and they too went bad due to alcohol exposure! SO! Unless you've checked resistance when the motor is fully warmed up, you can't be sure they are good. Typically the shellac-insulaiton on coils fails, it goes undetected until the coil is heated. There are a couple ways to take the resistance readings. How and under what teperature conditions did you test yours, may I ask?

Throttle Position Switch: Sometimes the TPS wiper is dirty or has failed. This too is FYI, and not related to closed loop per se'. By disconnecting the electrical plug you can operate the TPS through its enter throttle range while watching the (analog) resistance indicator on the VOM, looking for a smooth change in resistance through the entire range.

With the connector reassembled and the ignition switch to ON, motor OFF, the TB wiper should be set to 5.5 VDC.

O2 sensors:

The O2 sensor operation (including 'cross counts') can easily be monitored with a dynamic scan (most auto parts stores have that capability). And, also, the sensor can be removed and tested with a VOM and a propane torch.

https://axleaddict.com/auto-repair/How-to-Check-an-Oxygen-Sensor

A lazy (low # of cross-counts) or non-responding O2 sensor, especially an intermittently failing one can result in a number of closed loop symptoms (but not exclusive of closed loop operation either!) - especially idle irregularities and rough running, fouled plugs (on one bake only...is important to note) are some of the more common issues.

Not because of your symptoms in particular, but more of an FYI, you asked about checking the coils.

Well, the acid test for ignition is proper operation at WOT when the motor is fully warmed up! Furthermore, a pin-hole can develop in a wiring insulation that cannot be detected with a standard VOM: a MEGGAR or dedicated test equipment is required, which is uncommon except in the better repair shops.

The LT5 uses a "waste spark" design. Each coil fires two plugs at the same time.

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Ignitioncircuit-LT5.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Ignitioncircuit-LT5.jpg.html)

That said, the resistance can be measured across the spark terminals and compared with the readings across all 4 coils. (But, again, not all coils e.g., AC/Delco, MDS, Excel, etc. read the same, specifically, and may vary from type to type!) Plug wires resistance values vary too, depending on the make/type. However, the resistance should be proportional to their length; i.e., a wire twice as long as another should have close to twice as much resistance as the shorter one.


Well... w/o more specific info, this could get very superfluous (if not already!). So, I'll stop till I hear more specifics from you first.

:cheers:

Knocking sound doesn't go away when I depress the clutch pedal.

I changed the fuel filter (which is behind the front passenger wheel housing).

I'll try to find a fuel pressure gauge extension to run a dynamic test. Or, even easier would be to buy 2 new pumps at RockAuto...

I can't tell you at which temperature I tested the resistance of the injectors, I don't remember. I add this to my todo list (after changing the o2 sensor connector). I tested the resistance using this diagram:

http://i158.photobucket.com/albums/t120/sdba11/CheckingZR1FuelInjectorResistances.gif

For the TPS: can't I unplug it and hook a multimeter in the TPS plug to see the voltage fluctuation?

What's a VOM?

For the o2 sensor test, to be honest if I have to remove them I'll simply change them.

Coil packs: they'll be in my todo list as well as the spark plug wires, but pretty low on the list at the moment.

"Waste spark design", I think they are just like a 3.4 2000 Grand Am. And I'm pretty sure they even fit in there...

I just logged into this forum. After reading the site for the last year Ive just joined.

Ok, the knocking sound you have is the clutch unit on the AC compressor. Not a biggie, its just rattling around as you will see if you get closer and have a look. Thats why the sound will come and go. I had the same thing on mine, and I just replaced the clutch unit and its sweet as now.

Happy to read this. However, I'm not sure it's the problem. There is no change when I put A/C ON or OFF. I appreciate that you post on this thread as your first post!

Knocking sound is irregular, so I hope I can assume it is more a rattle than a knocking sound.

Actual todo list:

1. Fix o2 sensor connector.
2. Change spark plugs (I'm receiving my BKR7EIX11 plugs tomorrow, it can't hurt). I'll ask a mechanic nearby what he thinks of my old plugs.
3. Test the resistance on the fuel injectors (car hot).
4. Dynamic test fuel pressure.

[Dynomite]

What's a VOM?



VOM is a Volt Ohm Meter among other uses of the abbreviation VOM :D

One of the first tests I always do is a Compression Test on Zs which does not have much to do with your issue but just saying.

A compression test says a lot about the valves, Cylinders, and general wear of the engine. A compression test also says a lot about the uniformity of the wear among cylinders and uniform compression assures uniform work done by each cylinder.

Your first post suggests "Severe Buckings".
You have since suggested Knock.

You suggested the LT5 has behaved like this for 3,000 miles.
Also you suggested total power loss for a revolution or more but immediately returns to normal.

I have some ideas but what I do on ALL LT5s/ZR-1s is do my typical Top End after the Compression Test (The Compression Test is conducted to make sure I do not have Bottom End Issues). Once my Top End Restorations are complete the LT5s run perfectly with NO Codes for a very long time.

Part of that Top End of the LT5 includes the INFL REST restoration (the Air Bag Sensors re-grounded each side) including the Internal Wire each side. And part of that Restoration includes complete Brake Restoration and/or Installation of C5 Z06 Calipers and Rotors. Some more also but you get the idea :D

Oh....and my favorite Modification to ALL LT5s (Block TB Coolant at the Injector Housing).

[MuRCieLaGo]

VOM is a Volt Ohm Meter among other uses of the abbreviation VOM :D

One of the first tests I always do is a Compression Test on Zs which does not have much to do with your issue but just saying.

A compression test says a lot about the valves, Cylinders, and general wear of the engine. A compression test also says a lot about the uniformity of the wear among cylinders and uniform compression assures uniform work done by each cylinder.

Your first post suggests "Severe Buckings".
You have since suggested Knock.

You suggested the LT5 has behaved like this for 3,000 miles.
Also you suggested total power loss for a revolution or more but immediately returns to normal.

I have some ideas but what I do on ALL LT5s/ZR-1s is do my typical Top End after the Compression Test (The Compression Test is conducted to make sure I do not have Bottom End Issues). Once my Top End Restorations are complete the LT5s run perfectly with NO Codes for a very long time.

Part of that Top End of the LT5 includes the INFL REST restoration (the Air Bag Sensors re-grounded each side) including the Internal Wire each side. And part of that Restoration includes complete Brake Restoration and/or Installation of C5 Z06 Calipers and Rotors. Some more also but you get the idea :D

Oh....and my favorite Modification to ALL LT5s (Block TB Coolant at the Injector Housing).

Thanks for the definition of the VOM (quite simple)!

I always hated doing a compression test. It's like inspecting your girlfriend while she's asleep. Not sure I want to know the numbers. But I'll do it soon...

I've seen your (more than complete) threads. I like modding my cars, but I want to fix the initial problems before, or the car becomes garbage pretty quickly.

[secondchance]

These are from 94 manual but hopefully it would help.
http://i658.photobucket.com/albums/uu303/byongyun/Mobile%20Uploads/image_zpsyapl2l7w.jpeg (http://s658.photobucket.com/user/byongyun/media/Mobile%20Uploads/image_zpsyapl2l7w.jpeg.html)
http://i658.photobucket.com/albums/uu303/byongyun/Mobile%20Uploads/image_zpscllaa2q9.jpeg (http://s658.photobucket.com/user/byongyun/media/Mobile%20Uploads/image_zpscllaa2q9.jpeg.html)

[MuRCieLaGo]

secondchance I just looked at it and it's pretty much the same for a 1991. Thanks for the reference...

Updated todo list:

1. Finally, I do not need to fix my o2 sensor connector. I went to the scrapyard to find the connector on another vehicle and they all had the same problem. Local electric shop told me it's normal, there's no problem there.
2. Changed spark plugs.


To do:
3. Test the resistance on the fuel injectors (car hot).
4. Dynamic test fuel pressure.


Here's a picture of the plugs. Driver's side to the left, passenger's side to the right. All the plugs from the right side (passenger side) are pitch black, it's a bit better on the left side (driver side).

Why the code says that I'm running lean on the right bank? Pitch black means too much fuel, no?

http://i841.photobucket.com/albums/zz332/TiGarsRotatif/20160517_121156.jpg

[XfireZ51]

The sootiness of the plugs is a result of the lean condition the ECM is "seeing" so it's adding more fuel where it really doesn't need it. The O2 sensor must be broadcasting a lean condition which could be a result of a vacuum leak/exhaust leak bringing fresh air past the O2 and therefore it's reporting a "false" lean.

[MuRCieLaGo]

The sootiness of the plugs is a result of the lean condition the ECM is "seeing" so it's adding more fuel where it really doesn't need it. The O2 sensor must be broadcasting a lean condition which could be a result of a vacuum leak/exhaust leak bringing fresh air past the O2 and therefore it's reporting a "false" lean.

I know I got a vacuum leak. Tiny one, vacuum pump turns on one time every 3 seconds.

Exhaust leak is also VERY possible... Nobody mentionned it before but it makes sense.

Updated todo list:
3. Tested the resistance on the fuel injectors (car hot).

Primaries

#1: 17.8 ohms
#2: 17.8 ohms
#3: 17.9 ohms
#4: 17.9 ohms
#5: 17.7 ohms
#6: 17.6 ohms
#7: 17.5 ohms
#8: 17.5 ohms


Secondaries

#1: 17.8 ohms
#2: 17.8 ohms
#3: 17.8 ohms
#4: 17.8 ohms
#5: 17.5 ohms
#6: 17.5 ohms
#7: 17.4 ohms
#8: 17.3 ohms

To do:
4. Dynamic test fuel pressure.
5. Check for exhaust leaks.

[MuRCieLaGo]

Checked for exhaust leaks tonight, I got a tiny one on each side, about 6 inches after each o2 sensor.

Gonna get it fixed on next tuesday morning, but I don't think it'll fix something here.

[RussMcB]

I agree. I've noticed a couple leaks in my exhaust and they haven't affected how it runs (AFAIK).

[XfireZ51]

If the exhaust leak is behind the O2, what happens is that fresh air gets drawn in during times of high vacuum such as decel and idle. At cruise, vacuum
Is not so high and you won't see an issue.

[MuRCieLaGo]

If the exhaust leak is behind the O2, what happens is that fresh air gets drawn in during times of high vacuum such as decel and idle. At cruise, vacuum
Is not so high and you won't see an issue.

You're a bit right there. Gonna get it fixed as soon as possible anyway, you're giving me some hope now.

[G8nightman]

Checked for exhaust leaks tonight, I got a tiny one on each side, about 6 inches after each o2 sensor.

Gonna get it fixed on next tuesday morning, but I don't think it'll fix something here.


How did you test for the leak?

[XfireZ51]

Just to illustrate how a small leak can make a difference, I had been data logging and tuning my 84 Xfire. At low MAP and decel, I needed to constantly add fuel.
One day, I was looking behind the car and noticed one of the mufflers hanging a bit low. The joint at the muffler/exhaust pipe was loose. This was enough to skew results. And I had a catalytic converter that was between the muffler and Y-pipe between where the muffler joint was and the O2 sensor. It was pulling fresh air from the back to the front. So there really is no such thing as a "small exhaust leak" when it comes to emissions ECM controlled vehicles running closed loop.

[MuRCieLaGo]

How did you test for the leak?

Put my hand near the flanges/clamps and I felt some air.

Just to illustrate how a small leak can make a difference, I had been data logging and tuning my 84 Xfire. At low MAP and decel, I needed to constantly add fuel.
One day, I was looking behind the car and noticed one of the mufflers hanging a bit low. The joint at the muffler/exhaust pipe was loose. This was enough to skew results. And I had a catalytic converter that was between the muffler and Y-pipe between where the muffler joint was and the O2 sensor. It was pulling fresh air from the back to the front. So there really is no such thing as a "small exhaust leak" when it comes to emissions ECM controlled vehicles running closed loop.

I really need to do some researches regarding that closed loop thingy. I'm not sure I understand how it works.

Thanks a lot for your help.

[G8nightman]

I will be testing for leaks on my system was thinking of using a smoke machine..

[XfireZ51]

Put my hand near the flanges/clamps and I felt some air.



I really need to do some researches regarding that closed loop thingy. I'm not sure I understand how it works.

Thanks a lot for your help.

Closed Loop means that the ECM is using O2 sensors as one of the inputs for calculating injector pulse width. The VE tables are the main fueling tables and then the ECM utilizes O2 sensors to modify those values. There's more to it but this is the basic operation.

[MuRCieLaGo]

Small update today:

Been running with the car, knocking noise seems to be GONE since I changed the spark plugs...

New code showed up once today:

Code 42 - Electronic Spark Control Error.

[MuRCieLaGo]

Exhaust leak fixed - no change at all.

Gonna order two new o2 sensors.

[MuRCieLaGo]

Receiving two NGK NTK o2 sensors tomorrow. Meanwhile, car developped another symptom: stalls randomly at red lights (starts perfect when I crank it back).

[XfireZ51]

Could you recap the changes you made prior to all this happening?

[MuRCieLaGo]

Could you recap the changes you made prior to all this happening?

Good idea

RECAP

Problem: low rpm bucking, especially when cold. Stalling at red lights (restarts like a charm). Got codes 55 and 64 once, erased them and they never came back. Also experienced a strange knocking/rattling noise, which went away on its own.

-Electrically tested the injectors, hot. Got between 17.3 and 17.9 ohms everywhere.
-Spark plugs changed.
-Fuel pumps removed, visual inspection done: nothing was wrong.
-Fuel pressure tested. Idle: 41 psi, FP1: 46 psi, FP2: 48 psi.
-Fuel filter changed.

Receiving two NGK NTK o2 sensors tomorrow.

[LGAFF]

I think you have a bent DIS PIN

[MuRCieLaGo]

I think you have a bent DIS PIN

I searched and I found this thread, which shows the connector. However, where is that connector?

http://www.zr1.net/forum/showthread.php?t=20184

Should be easy to check?

[LGAFF]

under the plenum at the back of the intake

[MuRCieLaGo]

So...

1. Change both o2 sensors.
2. Remove plenum and check for that connector.

Should I check something else while the plenum is removed?

[XfireZ51]

Good idea

RECAP

Problem: low rpm bucking, especially when cold. Stalling at red lights (restarts like a charm). Got codes 55 and 64 once, erased them and they never came back. Also experienced a strange knocking/rattling noise, which went away on its own.

-Electrically tested the injectors, hot. Got between 17.3 and 17.9 ohms everywhere.
-Spark plugs changed.
-Fuel pumps removed, visual inspection done: nothing was wrong.
-Fuel pressure tested. Idle: 41 psi, FP1: 46 psi, FP2: 48 psi.
-Fuel filter changed.

Receiving two NGK NTK o2 sensors tomorrow.

I was curious as to what mods may have been done prior to all this.

[MuRCieLaGo]

I was curious as to what mods may have been done prior to all this.

Mods:

-Marc Haibeck's chip
-OBX headers
-Magnaflow resonator
-Borla catback

[XfireZ51]

Mods:

-Marc Haibeck's chip
-OBX headers
-Magnaflow resonator
-Borla catback

So is that when the motor started to misbehave?

[Paul Workman]

So...

1. Change both o2 sensors.
2. Remove plenum and check for that connector.

Should I check something else while the plenum is removed?

Well, obviously there's no time like the present (plenum off) to inspect everything and replace as necessary:


vacuum circuit, SPT actuators,
all electrical connections**,
hoses and clamps,
inspect/refresh starter solenoid contacts as needed,
inspect/clean the drain tube (under and at the back of the starter)
port matching.


**NOTE: When inspecting electrical connectors, be doubly certain NOT to accidentally misalign any pins as you reassemble them. And, due to the delicate nature and number of pins be especially attentive when reinstalling the long DIS connector; the one with the little bolt/hold-down screw in the center. (Ask me how I know...)

:cheers:

[MuRCieLaGo]

So is that when the motor started to misbehave?

No, I'm having the problems since I bought the car (before the mods).

Just removed plenum this morning. One of the DIS connector pin was BARELY bent, so I straightened it.

No change at all.

I inspected pretty much everything you mentionned Paul...

Gonna get my o2 sensors changed on a lift friday morning.

[Paul Workman]

No, I'm having the problems since I bought the car (before the mods).

Just removed plenum this morning. One of the DIS connector pin was BARELY bent, so I straightened it.

No change at all.

I inspected pretty much everything you mentionned Paul...

Gonna get my o2 sensors changed on a lift friday morning.

Well, I betcha you wish now you had installed those lateral bungs on the collectors like "someone" suggested, huh?:p

This whole episode screams for data-logging! I feel some of your frustration at this simple issue dragging on. And, (please forgive me if I'm wrong) I feel more frustration if you haven't data-logged it yet so we could maybe see what is going on when it 'bucks'. (There are some slick programs, e.g., Tunercat, etc., you can download to a laptop. With the appropriate cabling you can watch in real time everything going and often spot the issue in just a few minutes of actual driving!

No worries. When you finally nail it, you'll forget about all the trials and tribulation. :) And! You'll prolly know a lot more about the car than many do: nothing like hands-on experience, right?

Hope you can put this to bed pretty soon. :cheers:

[MuRCieLaGo]

Well, I betcha you wish now you had installed those lateral bungs on the collectors like "someone" suggested, huh?:p

Correct me if I'm wrong, but this whole episode screams for data-logging! I feel some of your frustration at this simple issue dragging on, and feel more frustration that (please forgive me if I'm wrong) you haven't data-logged it yet so we could maybe see what is going on when it 'bucks'. (There are some slick programs, e.g., Tunercat, etc., you can download to a laptop and with the appropriate cabling you can watch in real time everything going. And, sometimes that is the only way one can efficiently zero-in on what the problem is. Just sayin, buddy.

No worries. When you finally nail it, you'll forget about all the trials and tribulation. :) And! You'll prolly know a lot more about the car than many do: nothing like hands-on experience, right?

Hope you can put this to bed pretty soon. :cheers:

I'm thinking about taking it to the dealership. Can't they connect it to tell me what's the issue?

I still got hope for my new o2 sensors on friday though, it has been mentionned a lot of times that it could be the problem. I'd love to know how to data-log this car... But I hope I won't have to do that.

Thanks Paul!

[Paul Workman]

I'm thinking about taking it to the dealership. Can't they connect it to tell me what's the issue?

I still got hope for my new o2 sensors on friday though, it has been mentionned a lot of times that it could be the problem. I'd love to know how to data-log this car... But I hope I won't have to do that.

Thanks Paul!

Taking it to a dealership CAN be a huge can of worms, depending on the dealership's service (manager) department. (I have an independent mechanic shop - speed shop - that I'd trust waaaay before any stealership. Anyway, regardless they have to have the right firmware for Corvette OBD-I. (Dominic or Pete or Marc might chime in with specifics far better than I can).

I have an old AutoXray scanner that I use. It is hard to explain just how simple and how efficient it is if you have the ability to hook it up and in seconds pin-point the problem(s). Unfortunately, they no longer make or support this old gem, but there are several alternatives out there that will do the job.

In any case... I believe one of the FIRST recommendations was to get that puppy scanned. That might have saved a lot of this "trial and error" stuff, and you could be enjoying the car by now. :o Just sayin....

[MuRCieLaGo]

Taking it to a dealership CAN be a huge can of worms, depending on the dealership's service (manager) department. (I have an independent mechanic shop - speed shop - that I'd trust waaaay before any stealership. Anyway, regardless they have to have the right firmware for Corvette OBD-I. (Dominic or Pete or Marc might chime in with specifics far better than I can).

I have an old AutoXray scanner that I use. It is hard to explain just how simple and how efficient it is if you have the ability to hook it up and in seconds pin-point the problem(s). Unfortunately, they no longer make or support this old gem, but there are several alternatives out there that will do the job.

In any case... I believe one of the FIRST recommendations was to get that puppy scanned. That might have saved a lot of this "trial and error" stuff, and you could be enjoying the car by now. :o Just sayin....

I live in a 50,000 people city and literaly nobody can help me here scanning the codes, especially the dealership. But I think I found something...

I've got a major update for you guys.

Usually, I always run the car with the heater OFF. Yesterday, I pressed AUTO and forgot to turn it OFF. The car ran pretty bad. Just look at the idle when I press the AUTO button:

https://www.youtube.com/watch?v=ZCEla2ShgF4

May I repeat:

-I had a cluster flickering problem.
-Alternator was changed 1 day before I bought the car.
-3 weeks ago, I checked the alternator voltage when the car was cold. It was 14.3V. Checked it yesterday when the car was fully warmed, it was 13.8V. I believe this is perfectly normal.
-Tensioner pulley is loose, at idle only.

I'm not sure which way to go now.

And by the way, local garage couldn't change o2 sensors, because I told you local garages can't help me. They can only work on Cavaliers and stuff like that.

[Paul Workman]

Well, my sense of it is: (1) it isn't anything too big, but (2) it is beyond your current knowledge/(ZR-1) expertise.

I hate to see anyone struggle so. I'm thinking that perhaps you should consider either taking it to someone that IS ZR-1 savvy, or paying someone that is skilled to visit your location w/ tools in hand.

If neither of these are going to work, but you have reasonable mechanical skills, then I suggest you pick someone that is knowledgeable that will be willing to work with you, off-line. By "huddling" w/ someone off-line you have better continuity of thought and the troubleshooting process and less chance of distractions - albeit in the best of intentions. Just a thought.:cheers:

[XfireZ51]

Is the car driveable for long distances? What level of computer savvy do u have?

[secondchance]

Usually, I always run the car with the heater OFF. Yesterday, I pressed AUTO and forgot to turn it OFF. The car ran pretty bad. Just look at the idle when I press the AUTO button:


Once again, as far as irregular clanking noise when HVAC is turned on, check how close belts are at belt tensioner pulley to belt coming up from the water pump. I had very similar noise. Turned out to be belt being too long.

[Billy Mild]

If you need a cheap scanner buy ALDL droid for Android phone or tablet plus the Bluetooth dongle.

http://www.corvetteforum.com/forums/c4-tech-performance/3413413-finally-bluetooth-for-obd1-and-android.html

[MuRCieLaGo]

Well, my sense of it is: (1) it isn't anything too big, but (2) it is beyond your current knowledge/(ZR-1) expertise.

I hate to see anyone struggle so. I'm thinking that perhaps you should consider either taking it to someone that IS ZR-1 savvy, or paying someone that is skilled to visit your location w/ tools in hand.

If neither of these are going to work, but you have reasonable mechanical skills, then I suggest you pick someone that is knowledgeable that will be willing to work with you, off-line. By "huddling" w/ someone off-line you have better continuity of thought and the troubleshooting process and less chance of distractions - albeit in the best of intentions. Just a thought.:cheers:

I don't think it's a good idea there, Paul. I'm pretty far from everything here and I got a LOT of tools in my garage. If I lived in a big city, of course I would have been to a ZR-1 specialist...

Is the car driveable for long distances? What level of computer savvy do u have?

Just did a 150 miles trip today, so yes the car is driveable for long distances.

My computer level is easily intermediate-advanced. I'm the one that people call when their computer is broken (and full of virus most of the time).

Once again, as far as irregular clanking noise when HVAC is turned on, check how close belts are at belt tensioner pulley to belt coming up from the water pump. I had very similar noise. Turned out to be belt being too long.

secondchance, you've been useful to me a couple of times. I saw the thread that you posted a bit more than a month ago about that issue. Did you have some buckings/hesitations at low RPM? Did you have any other symptom other than that noise? As I can see, I can not adjust the tension on this belt, that's the tensioner's job, right? I tried to find a model number or something on the belt, unfortunately without success.

If you need a cheap scanner buy ALDL droid for Android phone or tablet plus the Bluetooth dongle.

http://www.corvetteforum.com/forums/c4-tech-performance/3413413-finally-bluetooth-for-obd1-and-android.html

This, is interesting...

[secondchance]

I think it's possible that you have more than one issue. YouTube posting of clanking noise at idle when HVAC is on (compressor engaging) is very similar to my experience. Bucking and hesitation maybe another issue.
Belt tensioner cannot be adjusted but belt lengths are available in 5 mm increments. When the drive belt is too long (and some belts sold as correct length for LT5 are 80.5 mm. I am currently running 80 mm) when AC pulley engage and disengage creating a light fluttering, tensioner bottoms out and starts tapping.

[MuRCieLaGo]

I think it's possible that you have more than one issue. YouTube posting of clanking noise at idle when HVAC is on (compressor engaging) is very similar to my experience. Bucking and hesitation maybe another issue.
Belt tensioner cannot be adjusted but belt lengths are available in 5 mm increments. When the drive belt is too long (and some belts sold as correct length for LT5 are 80.5 mm. I am currently running 80 mm) when AC pulley engage and disengage creating a light fluttering, tensioner bottoms out and starts tapping.

But like I said, I couldn't find a part number on the belt, so that's pretty sad... And yes, maybe I got more than one issue... Oh my god.

Reliable GM V8 they said...

[secondchance]

But like I said, I couldn't find a part number on the belt, so that's pretty sad... And yes, maybe I got more than one issue... Oh my god.

Reliable GM V8 they said...

You don't need a part number. Look at the gap between the belt pushed in by the tensioner and the belt going up from the water pump pulley to the alternator - narrowest pinch point. If this gap is less than 1-1/2", belt is too long and maybe causing the tensioner to bottom out. At $35-40 per belt, pretty cheap fix that takes one issue off the table. As for the stumbling, as others have suggested scanning May be the only way to avoid wild guesses and throwing parts on it. Problem with dealerships, perhaps not all but most, are more interested in making money than fixing cars. Furthermore, most LT5 certified Mr. good wrench have retired.

Don't get discouraged and check the belt for proper length. Also, figure out a way to access engine parameters when stumbling.

[KJL]

Any follow up?

[MuRCieLaGo]

Took a break - currently working far away from where I live.

To be continued.

Thanks!