90 - Running out of breath at 5000 - No Codes

[dondon]

Trying to figure out why my 90 5800 mile ZR1 (new owner) completely runs out of steam at 5000 RPM, it doesn't pull particularly hard to that point and really badly from 4000 RPM.

Background:
I previously had a code 61 - which I ended up replacing the solenoid, vacuum canister and secondary plastic piping. I checked the actuators and both openned quite easily. The car no longer throws a 61. When reassembling the solenoid had an extra nipple which I plugged (don't do this). which led to a hard code 56. Upon removing the plug, the 56 has gone away. The only modification that the car has is a Haibeck chip which is slightly detuned to handle the 90 Octane ethanol free gasoline.

I'm a bit of an odd case judging by other forum members in that I have original injectors, I don't believe the car should have injector problems as it has always run ethanol free gas. The fuel I'm using currently is 90 Octane Ethanol Free, as sold at a local Sonoco station.

Anyway, at this point I'm not getting any codes coming back. I've attached a datalog from datamaster. Its short and hopefully it tells enough of a story. Anyway, any assistance would be greatly appreciated. I haven't owned the car since new, so I can't say I know what a clean pull feels like, but as it stands the car quite often feels like it hesitates, and even at times it feels as though spark is cut momentarily then the car starts to pull again.

Any thoughts would be greatly appreciated.

[efnfast]

Sounds like the secondaries are not operating.

[dondon]

Sounds like the secondaries are not operating.

Thanks for the input. My thoughts are identical to yours... I just am at a loss as to how to get them to open. Especially given the actuators work, no code 61 and in the datalog, the ECM thinks the secondaries are open.

Does anyone know where in the FSM to look, or a local to Tampa/St Petersburg/Clearwater expert to talk to. I'd love the satisfaction of fixing it myself, but the end goal is to have another well running Z on the road.

[Paul Workman]

Assuming you have a "FULL POWER" indicator when the secondary's switch is ON, no codes, then I wonder now if you've got the "accordion" plastic intake tube is collapsing syndrome.

Mine was collapsing, at around 5000 rpm and falling on its nose too. It is a common problem with those old plastic "snorkels" - especially when the under-hood or ambient air temps are on the warm side. However there is cheap and easily fixed either by installing some of Marc's wire hoops to support the tube, or do as I did and build a sheet metal sleeve that slides inside the tube to smooth the air flow and keep the tube from collapsing.

Just a thought!

P.

[efnfast]

Good thinking Paul, does the new owner know how the seconday key works, and there is a light on the DIC that says "Full Engine Power"

[dondon]

Assuming you have a "FULL POWER" indicator when the secondary's switch is ON, no codes, then I wonder now if you've got the "accordion" plastic intake tube is collapsing syndrome.

Mine was collapsing, at around 5000 rpm and falling on its nose too. It is a common problem with those old plastic "snorkels" - especially when the under-hood or ambient air temps are on the warm side. However there is cheap and easily fixed either by installing some of Marc's wire hoops to support the tube, or do as I did and build a sheet metal sleeve that slides inside the tube to smooth the air flow and keep the tube from collapsing.

Just a thought!

P.

Hi Paul,

I will go out and purchase a stocking, make a temporary air filter and eliminate the snorkel to see if that is the issue. I have doubts on the snorkel theory as the car is smooth to 4500-5000 ish with the power key off, when the key is in the full power position, the car does all kinds of miss behaving prior to hitting the 5000 mark.

Thanks for the input, I'll likely get to this around Wednesday... have lots of crazy project work to do this week.

Thanks again
Jonathan

[dondon]

Good thinking Paul, does the new owner know how the seconday key works, and there is a light on the DIC that says "Full Engine Power"

Yes, sir the DIC shows Full Power. I would say that the key isn't perfect though, as I turn the key to where the on should be then have to rotate it back a smidge to get the light to turn on. Not sure if its possible that it could be switching states while driving, but the light stays strongly illuminated.

Best Regards
Jonathan

[efnfast]

My key can be a little tempermental. I think the contacts are dirty. I have to cycle the key sometimes to get it to activate

[Franke]

My key did the same thing until I took the switch apart and repaired/adjusted the contacts. It is important to the ECM that the switch is not flaky.

[dondon]

So, I looked through the datalog and noticed a bunch of knock. I put original PROM back in... things seemed better right off. So then I went to go drill it.

Code 61 - 5K max, but relatively smooth compared to before. So now what, did I install a faulty solenoid? bad vacuum canister? ECM?

Any thoughts on what I'm missing apart from the 5 hrs on Sunday. I really thought I got that 61 and fixed it.

[scottfab]

SECONDARY PORT THROTTLE VALVE SYSTEM error
But of course you know that.

Try seeing of the actuators pull in
http://www.zr1specialist.com/HAT%20Web/articles/Verifying%20Secondary%20Actuator%20Operation.pdf

If they do maybe your secondary fuel pump is tits up.
You could be running out of fuel but no code is set if it's not
lean enough to trip the code.

[dondon]

SECONDARY PORT THROTTLE VALVE SYSTEM error
But of course you know that.

Try seeing of the actuators pull in
http://www.zr1specialist.com/HAT%20Web/articles/Verifying%20Secondary%20Actuator%20Operation.pdf

If they do maybe your secondary fuel pump is tits up.
You could be running out of fuel but no code is set if it's not
lean enough to trip the code.

Thanks for your help with this problem. I have performed the check by shorting pin C17... unfortunately everything worked as it should, so now to keep checking till I find something.

I don't have equipment to check the fuel pump... so I'll have to take it in sometime this week. Thanks for the input.

[scottfab]

Thanks for your help with this problem. I have performed the check by shorting pin C17... unfortunately everything worked as it should, so now to keep checking till I find something.

I don't have equipment to check the fuel pump... so I'll have to take it in sometime this week. Thanks for the input.

Open the hood.
Engine off but ign key on.
Does the vacuum pump under the passenger side head light run?
Does it keep running without shutting off?

[dondon]

Open the hood.
Engine off but ign key on.
Does the vacuum pump under the passenger side head light run?
Does it keep running without shutting off?

It runs for a moment then stops.

FYI - the shorting of C17. While the actuators are moving, the pump runs, then shuts off again. Actuators stay open for as long as I'm patient enough to short the circuit.

[scottfab]

It runs for a moment then stops.

FYI - the shorting of C17. While the actuators are moving, the pump runs, then shuts off again. Actuators stay open for as long as I'm patient enough to short the circuit.

Sure sounds like secondaries are fine. Look to fuel pump #2 failure.
The only thing that puzzles me is that I'd expect a lean code to be set.

[Paul Workman]

Thanks for your help with this problem. I have performed the check by shorting pin C17... unfortunately everything worked as it should, so now to keep checking till I find something.

I don't have equipment to check the fuel pump... so I'll have to take it in sometime this week. Thanks for the input.

A lot of preliminary stuff can be done at home. (Besides, I don't know 'bout your situation, but there isn't any dealership I'd take an LT5 to for anything!)

As for checking the fuel pumps, all you need is a fuel pressure gauge that you can rent free from AutoZone** and a Volt Ohm Meter from Radio Shack or the like.

You can start by measuring current draw to the pumps. There is a fuel pump test connector jutting out of the same wire loom as the diagnostic connector, located near the top of the power brake booster, next to the firewall.

With the key off, and the VOM configured to read Amperes (most set up to read 10A) put the red lead to the positive terminal of the battery and the black lead to the little red pigtail. Each pump draws between 4-5A. So,if both pumps are running normally, you'll measure between 8 and 10 amperes, you'll hear the pumps running, and with a fuel pressure gauge connected to the Schrader valve, fuel pressure should be about 52 pounds, give or take a pound or so.

Configuring the meter to read amperes...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Fuelpumpcurrentcheck004.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Fuelpumpcurrentcheck004.jpg.html)

The red test connector connected (via a yellow jumper with alligator clips on each end - alligator clip leads available from Radio Shack) to the black lead of the meter.

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Fuelpumpcurrentcheck001.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Fuelpumpcurrentcheck001.jpg.html)

With the red lead connected to the positive post of the battery, the current draw is normally 8-10 amperes if BOTH pumps are running. If only 1/2 that current is present, then one of the pumps is either kaput or there is a connection issue (possibly).

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Fuelpumpcurrentcheck005.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Fuelpumpcurrentcheck005.jpg.html)

Then you can check the fuel pressure under driving conditions, by taping the pressure gauge to the windshield and monitoring the pressure at normal load and at WOT.

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)

Pressure should be in the mid 40s in normal driving loads, and "pop" up to 52 (give or take) at WOT.

If the fuel pressure is low, especially at WOT, it could mean a problem with a pump, OR the fuel filter. (The filter is next to the frame rail behind the right front tire, and under a heat shield.)

Since the secondaries tested OK, you might want to know what the resistance is across the injectors when they're HOT. They should read between 12-14 ohms (hot). If they read 10 ohms or less, it indicates problems likely. A reading of 8 ohms or less and the injector is definitely in need of replacement; not only to run better, but to prevent the possibility of a burnt valve (ask me how I know...). (The procedure is well laid out in the FSM.)

And, of course, the easy thing to do is change plugs.

[scottfab]

absolutely phenomenal wright up Clear easy to understand and easy to read
A lot of preliminary stuff can be done at home. (Besides, I don't know 'bout your situation, but there isn't any dealership I'd take an LT5 to for anything!)

As for checking the fuel pumps, all you need is a fuel pressure gauge that you can rent free from AutoZone** and a Volt Ohm Meter from Radio Shack or the like.

You can start by measuring current draw to the pumps. There is a fuel pump test connector jutting out of the same wire loom as the diagnostic connector, located near the top of the power brake booster, next to the firewall.

With the key off, and the VOM configured to read Amperes (most set up to read 10A) put the red lead to the positive terminal of the battery and the black lead to the little red pigtail. Each pump draws between 4-5A. So,if both pumps are running normally, you'll measure between 8 and 10 amperes, you'll hear the pumps running, and with a fuel pressure gauge connected to the Schrader valve, fuel pressure should be about 52 pounds, give or take a pound or so.

Configuring the meter to read amperes...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Fuelpumpcurrentcheck004.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Fuelpumpcurrentcheck004.jpg.html)

The red test connector connected (via a yellow jumper with alligator clips on each end - alligator clip leads available from Radio Shack) to the black lead of the meter.

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Fuelpumpcurrentcheck001.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Fuelpumpcurrentcheck001.jpg.html)

With the red lead connected to the positive post of the battery, the current draw is normally 8-10 amperes if BOTH pumps are running. If only 1/2 that current is present, then one of the pumps is either kaput or there is a connection issue (possibly).

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Fuelpumpcurrentcheck005.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Fuelpumpcurrentcheck005.jpg.html)

Then you can check the fuel pressure under driving conditions, by taping the pressure gauge to the windshield and monitoring the pressure at normal load and at WOT.

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)

Pressure should be in the mid 40s in normal driving loads, and "pop" up to 52 (give or take) at WOT.

If the fuel pressure is low, especially at WOT, it could mean a problem with a pump, OR the fuel filter. (The filter is next to the frame rail behind the right front tire, and under a heat shield.)

Since the secondaries tested OK, you might want to know what the resistance is across the injectors when they're HOT. They should read between 12-14 ohms (hot). If they read 10 ohms or less, it indicates problems likely. A reading of 8 ohms or less and the injector is definitely in need of replacement; not only to run better, but to prevent the possibility of a burnt valve (ask me how I know...). (The procedure is well laid out in the FSM.)

And, of course, the easy thing to do is change plugs.

[dondon]

Scott and Paul, thanks for the help. I've done some testing...

The good:
Bought a fuel pressure guage, hooked it up.
46 PSI when can is not on, 41 PSI when car has been started and was running. FSM and precious comments in this thread indicate 48 - 55 PSI before start up as the correct measurement. So its a bit low. As you know this doesn't necessarily test the secondary pump, unfortunately I couldn't find and extension pipe.

The Bad:
I couldn't get a reading on my Multimeter (testing red pig tail, on mine it appeared orange and black... not sure if I had the right one, but the location was identical). probably doing something wrong.

Next steps:
With the pressure being low, I'm going to buy a new fuel filter, and 2 pumps. Hopefully in a week I can report back and say its happy days. Its going to be a big week for the little Z, it should have new shoes arriving this week.

Thanks again for all the help, if the plan of action doesn't make sense please let me know.

As for dealers... I've found a locally owned not Chevrolet dealership that keeps me quite satisfied, prices aren't that dissimilar to a dealership, but I trust them and that's more important to me.

[Paul Workman]

As for dealers... I've found a locally owned not Chevrolet dealership that keeps me quite satisfied, prices aren't that dissimilar to a dealership, but I trust them and that's more important to me.

You know best, but these cars are older than a lot of people working at some shops, and most(?) have never seen an LT5 before. These pages are filled with horror stories. Just sayin. SGC is Georgia, if that helps.

As for the high pressure reading, depending on whether there is perhaps air in the fuel line, the pressure may not peg at the 55# due to the secondary pump is shut off in a couple seconds. With the ignition switch OFF, connect the positive terminal of the battery to the red test connector on the wire loom and see what your fuel pressure is then. After a couple seconds, with both pumps running, the pressure should be in the 52-55# range. If it is, then the pumps are running.

However, see if you can find an extension (got mine at AutoZone too) to observe dynamic fuel pressure. Only then you will know if the system will provide fuel at the rate required at WOT. If, for example, the fuel filter is choked up, the pressure will drop across the filter, indicating the pumps are probably OK, but there is a flow issue.

Change the pumps if you want. But, I hate to see you changing parts in place of troubleshooting. That is how unforeseen variables get introduced to the initial issue, e.g., infant mortality, is the term applied to new parts that failed "out of the box".

Good luck!

P.

[scottfab]

41psi is not low. It's way low.
Yes fuel filter on GP first if you're not sure how long it's
been but note likely the issue.
You're sitting right on the problem I'd say.
One or both fuel pumps. If you get 41 at about idle
imagine how it may drop off under high demand.
Best investment would be an extension and some tape.
Seems prudent before proceeding.

A note about the pig tail. It's the only one at that
location so unless someone added something you've got it.
It ONLY works as a test when the key is off. It does nothing
with key on because the way it is routed through the relays.
ALSO important to note with key off and applying 12v to the
pig tail you get BOTH pumps running. It's a great static test.
From there you can remove one or the other of the fuel pump
fuses to see what pressure each pump can do. You do not want run
these pumps for long periods of time through the pig tail. Just saying.... do each test, not the pressure and shut it off.

As for a place to work on your car. YOU will be the best influence
on how well they do with the car but you have to study up here
on the forum and show them the results.

[dondon]

41psi is not low. It's way low.
Yes fuel filter on GP first if you're not sure how long it's
been but note likely the issue.
You're sitting right on the problem I'd say.
One or both fuel pumps. If you get 41 at about idle
imagine how it may drop off under high demand.
Best investment would be an extension and some tape.
Seems prudent before proceeding.

A note about the pig tail. It's the only one at that
location so unless someone added something you've got it.
It ONLY works as a test when the key is off. It does nothing
with key on because the way it is routed through the relays.
ALSO important to note with key off and applying 12v to the
pig tail you get BOTH pumps running. It's a great static test.
From there you can remove one or the other of the fuel pump
fuses to see what pressure each pump can do. You do not want run
these pumps for long periods of time through the pig tail. Just saying.... do each test, not the pressure and shut it off.

As for a place to work on your car. YOU will be the best influence
on how well they do with the car but you have to study up here
on the forum and show them the results.

Thanks for the insight on how the pigtail is intended to function, I'm a newb at this.

I've ordered a fuel filter, in hindsight I should have just bought one from a local store and had instant results. I will pickup the long hose likely today, and that way be able to run a test tomorrow (filter should arrive same day).

If it is the fuel pump. Which one should I get, I seem to remember running into a previous post of yours where you weren't such a big fan of the Airtex

On 06-12-2012:
"I wouldn't touch an Airtex ever again. My first "How to" on a fuel pump replacement ended in the Airtex failing. Maybe I just got a bad one but not willing to take a chance again. The flow rate on the P240KC is just fine for a stock engine. "


Would you recommend the P240KC or something else?


Thanks again to this community for being so helpful, experience really is the key to success with this IMHO

[XfireZ51]

Suburban or Tahoe pumps work fine.

[Kevin]

41psi is not low. It's way low.
Yes fuel filter on GP first if you're not sure how long it's
been but note likely the issue.
You're sitting right on the problem I'd say.
One or both fuel pumps. If you get 41 at about idle
imagine how it may drop off under high demand.
Best investment would be an extension and some tape.
Seems prudent before proceeding.

A note about the pig tail. It's the only one at that
location so unless someone added something you've got it.
It ONLY works as a test when the key is off. It does nothing
with key on because the way it is routed through the relays.
ALSO important to note with key off and applying 12v to the
pig tail you get BOTH pumps running. It's a great static test.
From there you can remove one or the other of the fuel pump
fuses to see what pressure each pump can do. You do not want run
these pumps for long periods of time through the pig tail. Just saying.... do each test, not the pressure and shut it off.

As for a place to work on your car. YOU will be the best influence
on how well they do with the car but you have to study up here
on the forum and show them the results.

i thought 42 psi at idle was normal and 52ish when the secondaries kick in

[scottfab]

i thought 42 psi at idle was normal and 52ish when the secondaries kick in

I always tell people to be suspicious of any idle pressure below 43. It is one of those threshold values that should lead to more investigation. In my case it was a bad fuel pump that could not get higher than 41.
Easy to find out. Pinch the regulator vacuum. A really good pump will hit above 53 a mediocre one will be just above 50. Anything less than 50 is crap especially if it is new.

[scottfab]

....snip....
On 06-12-2012:
"I wouldn't touch an Airtex ever again. My first "How to" on a fuel pump replacement ended in the Airtex failing. Maybe I just got a bad one but not willing to take a chance again. The flow rate on the P240KC is just fine for a stock engine. "


Would you recommend the P240KC or something else?


Thanks again to this community for being so helpful, experience really is the key to success with this IMHO


Yes that is my quote from a different thead. Aritex let me down. As for PERFORMANCE ELECTRIC Part # P240KC
I put two of them in a bit over a year ago and have been happy with them. Just yesterday I was testing them :p

[RedSled]

My recent lack of power issue turned out to be bad ignition wires. And they only had about 8K miles on them.

[dondon]

So the potential fuel pump problem has been resolved. I installed 2 P240KC fuel pumps (if you are fearful of doing this, don't be it was very very easy - I have no prior experience with this stuff - <2 hours should probably be 45 minutes) and a fuel filter. Immediately after doing the swap I went for the excited test drive... same issue and saw a SES light very soon after start. Went home, hooked it up - Code 65 Rich Exhaust... I reset it and went for another test drive just to hopefully confirm the problem... Code 61 - Secondary Port Throttle.

Anyway, I'm a little confused as to what the problem is and where to find it. I recently replaced much of the whole secondary vacuum deal(solenoid and spider tubes). I hooked up the Tech 1 I recently acquired and noticed the Secondary Vacuum is 0 KPA. It does not move from this number. So I thought maybe I have a bad sensor, hooked up my handheld vacuum pump, and watched the secondary sensor work and show changes in vacuum in accordance with what I was doing.

So I feel at a loss for finding the leak. I've checked the pipe leading from the pump to plenum, and no leak also the vacuum pump does stop shortly after energizing and stay off. I had previously followed the code 61 instructions on this forum and I'm unsure of what I can do differently if I pull the thing apart again. Is there a good restart point or something obvious I may have missed. Any thoughts are welcomed.

Best Regards
Jonathan

[Franke]

I don't know if I can be of much help but looking at the FSM for a 1990 on page 6e3-c1-11and 12, It shows the vacuum and voltage at normal and full power switch settings. Normal mode should be 0.0 kPa and .54 - .62 volts at all times. Full power mode should be 33-66 kPa and 1.3 - 3.1 volts with the Tech1 tool.
You won't have full secondary operation if an engine code is present.
I am also wondering if the ECM is not recognizing full power mode for some reason even though the FP switch is on. Chart C1-F on page 6e3-c1-22.

[scottfab]

Jonathan, here is way to operate the secondaries with the plenum in place. This will allow you to test them and actually see them pull in without rolling down the highway.

I agree with all in this article except the assertion that 1 sec cycle time on the pump is ok. It states that that having a longer cycle time does not affect the engine power. While this is correct, to leave a system with this amount of leakage is just asking for the pump to cycle itself into oblivion. I'd investigate and fix a vacuum system that cycled 10 sec or less. So anyway, try this and actuate the secondaries several times. If they seem to pull in on both sides, clear any codes then go for a drive and see. If it drops out again look to see what codes are set again and we can go from there.


http://www.zr1specialist.com/HAT%20Web/articles/Verifying%20Secondary%20Actuator%20Operation.pdf

[dondon]

I don't know if I can be of much help but looking at the FSM for a 1990 on page 6e3-c1-11and 12, It shows the vacuum and voltage at normal and full power switch settings. Normal mode should be 0.0 kPa and .54 - .62 volts at all times. Full power mode should be 33-66 kPa and 1.3 - 3.1 volts with the Tech1 tool.
You won't have full secondary operation if an engine code is present.
I am also wondering if the ECM is not recognizing full power mode for some reason even though the FP switch is on. Chart C1-F on page 6e3-c1-22.

Thanks Franke, I went through the manual on these sections, and will go ahead an apply the FP test. If the rich exhaust comes back I'll run the other test. Thanks again for the input, and nice easy to get at locations in the FSM - I have a digital copy bought from WRP - and its a bit of a PITA to look at more than one page at a time.

[rhipsher]

Don! Three words. Secondary vacuum solenoid.

[dondon]

Jonathan, here is way to operate the secondaries with the plenum in place. This will allow you to test them and actually see them pull in without rolling down the highway.

I agree with all in this article except the assertion that 1 sec cycle time on the pump is ok. It states that that having a longer cycle time does not affect the engine power. While this is correct, to leave a system with this amount of leakage is just asking for the pump to cycle itself into oblivion. I'd investigate and fix a vacuum system that cycled 10 sec or less. So anyway, try this and actuate the secondaries several times. If they seem to pull in on both sides, clear any codes then go for a drive and see. If it drops out again look to see what codes are set again and we can go from there.


http://www.zr1specialist.com/HAT%20Web/articles/Verifying%20Secondary%20Actuator%20Operation.pdf

Hi Scott

Thanks for the info. FYI - car feels as though it starts quicker with new fuel pumps.

I've already run that test with success and it holds the actuators open as long as I want them to be open (was shorting the circuit on the front suspension arms). Pump runs while actuators are moving then shuts off again immediately and never turns on until the actuators are energized again.

These are the vacuum tests I previously ran:

Passenger side connector to the pump (by the oil filter), if I vacuum test it holds in both directions. If I pull the cylinder 3/5 vacuum pipe, it holds going down, but going into the plenum(metal side), I cannot get vacuum to hold.
Vacuum test Map sensor by the battery / ECM, the pipe does not hold vacuum, but the Map sensor does.
Vacuum test MAP sensor behind plenum, vacuum holds on the sensor, but does not hold going back into the plenum.

Don't think any of the above is a problem but in the interests of full information.

I think I'm going to try something ODD prior to pulling the plenum off again (its on the outer edge of my comfort level). Add vacuum to the sensor under the ECM, and pinch the pipe off when its in the range that Franke Specified, and then block the spider vein that would run to the sensor. My expectation is that and I am probably wrong... the sensor will be within range, the ECM will activate the secondaries and the pump will provide all vacuum necessary. If it runs well then I think the problem is somewhere in the spider vein headed to the sensor, but then again maybe not. This is not my area of expertise.

Thanks for the continued help
Jonathan

[scottfab]

Hi Scott

... snip...
I think I'm going to try something ODD prior to pulling the plenum off again (its on the outer edge of my comfort level). Add vacuum to the sensor under the ECM, and pinch the pipe off when its in the range that Franke Specified, and then block the spider vein that would run to the sensor. My expectation is that and I am probably wrong... the sensor will be within range, the ECM will activate the secondaries and the pump will provide all vacuum necessary. If it runs well then I think the problem is somewhere in the spider vein headed to the sensor, but then again maybe not. This is not my area of expertise.

Thanks for the continued help
Jonathan

You will be an expert at the end of it all.
Can you confirm. No codes are set AND the loss of power is always at 5000rpm? (each and every attempt?)

[dondon]

You will be an expert at the end of it all.
Can you confirm. No codes are set AND the loss of power is always at 5000rpm? (each and every attempt?)


I tried the
Add vacuum to the sensor under the ECM, and pinch the pipe off when its in the range that Franke Specified, and then block the spider vein that would run to the sensor. My expectation is that and I am probably wrong... the sensor will be within range, the ECM will activate the secondaries and the pump will provide all vacuum necessary.

Surprise surprise - I was wrong :). So it immediately set a HARD Code 61, the ECM clearly is smart enough to know I was messing with it.

Anyway, I reset the code, hooked up the plumbing as it was before and. went for a ride. Car ran as before, with same symptoms. The code 61 is intermittent... meaning the code gets stored, it does not have the hard stop at 3000 rpm as you see when the service engine soon light is on.

So maybe I need to setup a video... the car accellerates, and it feels brisk, probably within a second it feels less brisk but continues accelerating to 4000 with some force from 4000 to 5000 acceleration is slow and at 5000 I run out of patience and shift (usually I'm in 1st and 2nd gear), as I'm in the city.

Easiest way to get the code 61 stored is to get on the the highway in a high gear at low speed and mash the accelerator.

http://www.zr1specialist.com/HAT%20W...0Operation.pdf - what does this test eliminate any items from the suspect list
- actuators [yes / no]
- solenoid [yes / no]
- reservoir tank [yes / no]
- front portion of vacuum system pipes [yes / no]
- check valve near solenoid [yes / no]

My gut feel says and the secondary vacuum number is the big clue, does anyone know perhaps if it stays at 0 kpa like mine does, and at which point that changes. ie does it change when the secondary pump charges the system or some other time. All I can think is something under the GD plenum is preventing Vac from getting to the Vacuum sensor under the ECM... there may be other issues as I recently replaced the solenoid, reservoir tank and spider hoses... so who knows.

There is so much info on this forum about the code 61, you would swear I was deaf to something or overlooked something.

[Franke]

Looks like you've replaced almost everything in the secondary's operation and your tests on the "plumbing" seem ok. Do you have a spare ECM?

[John Boothby]

Don! Three words. Secondary vacuum solenoid.

I rebuilt my entire secondary vac system with brand new parts and after about 1 month one of the actuators went bad as well as the secondary solenoid. These were new items. I replaced the actuator with the old one, which was still good, and installed a new solenoid, and all has been fine since then.

I will bet that when you find the problem, it will be something simple.

[rhipsher]

There is another thing you should check. There are two check valves. One up front and one in back. The one in back is for cruise control which does not affect the secondaries. But the one that's up front can. It should only allow flow in one direction. So disconnect it and blow through both ports. If you can blow through both ports then there is some dirt inside of it causing the little BB ball to remain stuck. Just run some soap and water through it and blow it out with some compressed air. Then test it again.

[dondon]

There is another thing you should check. There are two check valves. One up front and one in back. The one in back is for cruise control which does not affect the secondaries. But the one that's up front can. It should only allow flow in one direction. So disconnect it and blow through both ports. If you can blow through both ports then there is some dirt inside of it causing the little BB ball to remain stuck. Just run some soap and water through it and blow it out with some compressed air. Then test it again.


Is this something I can do with plenum in place?

To be specific I'm trying to test :http://www.zr1netregistry.com/Portals/0/Images/TechArticle/vachoseasm.jpg

The check valve located to the left of the tag in this picture.

Any way to do this with plenum in place? It will add about a weeks lead time in order to get gaskets etc to do this job.

Thanks for input.

[rhipsher]

Is this something I can do with plenum in place?

To be specific I'm trying to test :http://www.zr1netregistry.com/Portals/0/Images/TechArticle/vachoseasm.jpg

The check valve located to the left of the tag in this picture.

Any way to do this with plenum in place? It will add about a weeks lead time in order to get gaskets etc to do this job.

Thanks for input.No!

[rhipsher]

I assume your gaskets are original. Otherwise I just cut my own Felpro gaskets and reuse them. But my setup is a bit different then yours. I have finolic spacers sandwiched between the plenum and IH which blocks coolant from making it into the plenum. So I would just order the stock gaskets from Jerry.

[scottfab]

....snip....

My gut feel says and the secondary vacuum number is the big clue, does anyone know perhaps if it stays at 0 kpa like mine does, and at which point that changes. ie does it change when the secondary pump charges the system or some other time. All I can think is something under the GD plenum is preventing Vac from getting to the Vacuum sensor under the ECM... there may be other issues as I recently replaced the solenoid, reservoir tank and spider hoses... so who knows.

There is so much info on this forum about the code 61, you would swear I was deaf to something or overlooked something.


I'm going to propose a negative test. That is a test where you force a failure and see if the outcome is what is expected. Pull the power to the vacuum pump and go for a WOT. Do the secondaries pull at all? When does it give out? (in rpm)
If the only vacuum to the actuators is the pump then the secondaries will not pull in at all.

[XfireZ51]

If the secondaries are shutting down due to lack of vacuum, should be getting a 61 if full power is ON. Have you shut down Full Power and run it up that way?
Does it still "run out of breath" and exactly what does that mean?
Bucking, stalls, breaking up simply not accelerating as much?

[scottfab]

If the secondaries are shutting down due to lack of vacuum, should be getting a 61 if full power is ON. Have you shut down Full Power and run it up that way?
Does it still "run out of breath" and exactly what does that mean?
Bucking, stalls, breaking up simply not accelerating as much?

From post #27

...snip...
.. I reset it and went for another test drive just to hopefully confirm the problem... Code 61 - Secondary Port Throttle.
...snip...

Also in post #6 he states all runs smoothly with power key off.

With the pump disabled I would expect a flattening of power earlier than 5000rpm. If that happens then we know the pump is helping but what if the pump vacuum capacity is diminished? or???? The data point is finding out what happens with the pump unplugged.

[Franke]

Dondon, what Scott is suggesting has merit especially since the vacuum required has to remain above 41kPa to operate the SPT valves. 41kPa is about 12 inches HG. Code 61 is set in FP mode when the vacuum monitor senses vacuum below 21 kPa (3.5 in HG). When you mash the accelerator, the manifold vacuum drops toward atmospheric value (very low vacuum) and the vacuum pump starts to supplement the manifold vacuum in the vacuum reservoir to keep the SPT valves open. I would test the vacuum pump to verify its capacity to pull at least that much vacuum. Chart C-2D on page 6e3-c2-32 and 33 may be helpful. This is an attempt to eliminate any external items before plenum pull as suggested by Ripsher to get at that check valve underneath.

[dondon]

Dondon, what Scott is suggesting has merit especially since the vacuum required has to remain above 41kPa to operate the SPT valves. 41kPa is about 12 inches HG. Code 61 is set in FP mode when the vacuum monitor senses vacuum below 21 kPa (3.5 in HG). When you mash the accelerator, the manifold vacuum drops toward atmospheric value (very low vacuum) and the vacuum pump starts to supplement the manifold vacuum in the vacuum reservoir to keep the SPT valves open. I would test the vacuum pump to verify its capacity to pull at least that much vacuum. Chart C-2D on page 6e3-c2-32 and 33 may be helpful. This is an attempt to eliminate any external items before plenum pull as suggested by Ripsher to get at that check valve underneath.


Happy Chart C-2D everyone. Following the instructions led me right to:
Faulty Hose or Blockage in hose or faulty check valve.

The pump pulls at 14HG is anyone is interested... so anyway, it looks like the plenum pull going to become a reality. When I had it off last, I replaced the original spider assembly with one I ordered, so now I must pull it apart and test the plastic pipes until I find the blockage / check valve / faulty hose. I'm a little nervous to reorder from same vendor given the problem (has never worked since the rebuild), but that may just be par for the course... I'll likely assemble hoses from my previous set to make it work well.

This sure does explain the 0kpa on the vacuum sensor.

I will let everyone know once its back together to let everyone who know whether this was finally it... or there are more issues - I really hope I can just enjoy the car now for a bit.

[Franke]

dondon, I used steel brake line to replace many of the under plenum pipe and the one that comes out to the vac pump. Just a thought. Just another thought of something else... Could the check valve be installed backwards since you replaced the stuff?

[rkreigh]

plenum pull is a little intimidating, but do some searches and there are MANY step by step tutorials, with lots of nice pics. another recommendation is to buy marc haibecks DVD

once you watch it, you'll be more confident. you can even use the "top tool" as it fits but it's best to get a nice long shank torx

anyway, you are doing great troubleshooting the car and are almost home

I had the same exact issue, and it was the secondary act switch that went bad. it would only "code occasionally" until it went "all the way bad"

but I consitently have problems with the stumble at WOT and the car would buck and fall on it's face.

if you run into problems or don't want to attempt the plenum pull. mosey on over to see Aaron Scott at SGC and he's have you back on the road in nowtime

plus, Thomasville is nice this time of year.

hey, anyone going to SGC????

[rhipsher]

Don I bought my 1990 Z knowing before I wrote that $22,500 check that there was something wrong with it running out of breath at 4k. And was on the fence about buying my first Chevy that could turn out to be a lemon. But I was already a shade tree mechanic and felt confident or cocky enough that it was just a bad component somewhere and I could fix it. It took me a month and several plenum pulls until I found that the bad component was the secondary vacuum solenoid. And after I buttoned the plenum up fully expecting the same ole running out of breath at 4k and throwing another code 61 ses light. I was shocked when I mashed the gas peddle. There was no doubt it was fixed. The acceleration difference was undeniable. No ses light ever again. Acceleration all the way up passed 7k and really fast up to 7k. So hang in there. You will get it. It took me a month to figure it out. Sometimes finding the fix doesn't happen over night.

[dondon]

I think I'm out of ideas. Today I pulled the plenum... It was quite pleasurable. Anyway, I connected each vacuum pipe individually and tested for a blocked pipe, I tested the check valve. It all appears in order. I then took some volts off the battery and heard the solenoid operate. Continued testing.

In FSM on page 6E3-A-83 - the code 61 error chart. I went through the motions.
"Faulty Connection or Open CKT 930 or Faulty ECM" is where I ended up this was after the connect terminals A and B and enable "Field Service Mode" with "Scan" tool is test light "On" step.

CKT 930 is the connector to C17 (prior to removing plenum during previous diagnosing). Which when shorted operates the actuators... so can it be assumed from the above I have a bad ECM or are there some other tests I can run to avoid a potentially unnecessary parts spend or is it a case of just suck it up and try to source an ECM?

I have the plenum off and will likely leave it off until I'm sure I've tested everything that could be a miss. So any other good tests to get through would probably be good to get out the way.

Thanks Again

[Franke]

Judging from what you just described it appears that you have good voltage to the solenoid but don't have ground coming from the ECM when commanded by tech tool to enable field service mode. I would verify the c17 pink wire (ground) from the ECM at the ECM connector to see if it is resistive or open and then test continuity on that wire from the ECM connector (C17) back to the PTV solenoid. After all this testing the only thing left is the ECM.

[scottfab]

First off keep your momentum. Your tenacity will pay off.

Some ideas below. But what if it's not fuel and not the secondaries opening that is the problem? What if the CATs are blocked by soot etc on the front end? The symptom would be loss of power at higher rpm. My brothers vett had this issue. The bad new is I haven't the slightest idea how to check for that. On my brothers car I took the header off and looked down in there. I saw blockage and punched a long screw driver through the ceramic CAT. This fixed his problem but he then had to get new CATs. See below for ideas on secondaries.


...snip...
CKT 930 is the connector to C17 (prior to removing plenum during previous diagnosing). Which when shorted operates the actuators... so can it be assumed from the above I have a bad ECM or are there some other tests I can run to avoid a potentially unnecessary parts spend or is it a case of just suck it up and try to source an ECM?

Based on the fact that you get some secondary action up to 5000 I'm going to say the ECM is ok. Based on the charts at the bottom of this page it the secondaries were not opening at all you'd get no big pull up to the 5000 mark which I assume you are. That shows the ECM signal works. You could also verify the voltage at C17 while driving. It should go to 0V and stay there at WOT. If it does and the car still flattens at 5000rpm that shows the issue is not with the ECM and likely not with the secondaries based on the other C17 test you did.
http://www.zr1netregistry.com/Information/TechNet/EngineDrivetrain/Engine/tabid/137/articleType/ArticleView/articleId/101/categoryId/27/Secondary-Port-Vacuum-Diagnosis.aspx

I have the plenum off and will likely leave it off until I'm sure I've tested everything that could be a miss. So any other good tests to get through would probably be good to get out the way.

Thanks Again

Before reassembling rig a wire onto the each actuator such the you can physically pull on one and then the other as you are at 5000rpm and you feel the sag. You have to be creative in routing the wire using the wiper shaft as a pulley then around through the window. If power returns you need to stay looking at the secondaries and not fuel or CAT blockage.
ALSO before reassembly.....
Just for grins. Can you disconnect the pump way up where it connects into the vacuum reservoir tank? Then turn the key on to activate the pump. Does it continue to run >60 sec? Now plug the line you pulled. Does it run <10sec? The "re-verifies" that the pump is not blocked AND that it's vacuum contribution is making it to the reservoir.
http://zr1.net/forum/picture.php?albumid=189&pictureid=1351

[A26B]

If concerned about the secondaries not opening fully, just tie them open & go for a drive. It won't hurt a thing & if it runs out great, you will know for sure it's a secondary port throttle issue.

[Franke]

Some more thoughts. In a previous post you indicated a intermittent code 61 then later a solid code 61 in full power etc. Have you checked the sec solenoids for amount of vacuum needed to open the secondary's as suggested in Marc Heibeck's ZR-1 specialist test. Should operate at about 6 inches of vacuum. Also, the FSM says that there are various sensor inputs in an acceptable range required by the ECM to turn on the secondary's.

[dondon]

Some more thoughts. In a previous post you indicated a intermittent code 61 then later a solid code 61 in full power etc. Have you checked the sec solenoids for amount of vacuum needed to open the secondary's as suggested in Marc Heibeck's ZR-1 specialist test. Should operate at about 6 inches of vacuum. Also, the FSM says that there are various sensor inputs in an acceptable range required by the ECM to turn on the secondary's.

The code 61 is an intermittent code 61. My apologies for not stating that correctly. I did receive a solid 61 when I tried to be smart and trick the computer but adding vacuum to the sensor and keeping vacuum on it. I think the sensor assumed there was an issue with the solenoid since I believe (and I'm an amateur) that the vacuum only exists when the solenoid is activated. So the computer knew that it was being messed with and set a 61.

I did have a chat to GK today for a bit, he isn't of the belief there are ECM problems and gave me a laundry list of other things to check prior to going the ECM route. I'd love to know a hard and fast rule for knowing you have an ECM problem.

For the benefit of others GK mentioned that the power key even though the light is on requires a very strong connection and so I should recheck that as well as checking the pins on bolt on connector to the plenum, to ensure I'm getting a good ground. So I'll start there and keep working at it.

Thanks again to everyone for the continued support with this issue.

[dondon]

Today it lives. Took 5 months of very part time tinkering and it finally does everything that was expected of it.

So the problem appears to have been 2 fold. The fuel pumps, even though I could not confirm the others were shot, at bare minimum their check valves did not work, they were replaced with the rather well priced $23 models... This made the car run a lot smoother, but the 5000 issue persisted.
Today, I was staring that that ECU and wondering what kind of black box magic it was performing since everything about it seemed to work with the exception of the secondaries. On advice from another forum member I continued tinkering instead of getting it rebuilt. From pure irritation since if the C17 pin were shorted the secondaries opened I took the harnesses off of the ecu and stared at them for a while, tugging and pushing on C17 to see if it were somehow loose. Anyway, put it back together did a secondary output test and saw the secondary vacuum pressure go up... something that hadn't happened prior. I went for a spin and like magic it ran well.

So in summary new fuel pumps and a loose ECU connector?

I'm sure I'll likely have an issue with this again at some point, but for now HAPPY DAYS!

[Franke]

Good for you Dondon. Way to go! :)