'91 missing and would like a second opinnion

[ZR-1Mikko]

I was hoping I could have figured this one out, but after a bunch of diagnostics I'm not really sure where to look next. So I would appreciate your guys second opinion.

At this point I have already measured, coils, wires and injectors and they are all perfect and also less than 1 year old. Also installed new plugs and they all look fine after my test runs. Also I do not get a check engine light.
Car starts fine and runs perfect on idle. As soon as it warms up even a little bit the idle becomes rough and I start to hear occasional knock. when I take off it runs like a 70's vette at start and sometimes starts running smooth when I hit about 2000rpm. When I get it running normally under a steady throttle it runs fine, but starts stuttering when I step on it.

So I'm wondering if O2 sensors could cause this and not give a check engine light or could it be the fuel pump?

[secondchance]

I was hoping I could have figured this one out, but after a bunch of diagnostics I'm not really sure where to look next. So I would appreciate your guys second opinion.

At this point I have already measured, coils, wires and injectors and they are all perfect and also less than 1 year old. Also installed new plugs and they all look fine after my test runs. Also I do not get a check engine light.
Car starts fine and runs perfect on idle. As soon as it warms up even a little bit the idle becomes rough and I start to hear occasional knock. when I take off it runs like a 70's vette at start and sometimes starts running smooth when I hit about 2000rpm. When I get it running normally under a steady throttle it runs fine, but starts stuttering when I step on it.

So I'm wondering if O2 sensors could cause this and not give a check engine light or could it be the fuel pump?

Are you running factory original injectors? One form of injector failure occurs when injectors warm up. When cold, they operate fine.
Your symtom is similar to what I had.

[tccrab]

I was hoping I could have figured this one out, but after a bunch of diagnostics I'm not really sure where to look next. So I would appreciate your guys second opinion.

At this point I have already measured, coils, wires and injectors and they are all perfect and also less than 1 year old. Also installed new plugs and they all look fine after my test runs. Also I do not get a check engine light.
Car starts fine and runs perfect on idle. As soon as it warms up even a little bit the idle becomes rough and I start to hear occasional knock. when I take off it runs like a 70's vette at start and sometimes starts running smooth when I hit about 2000rpm. When I get it running normally under a steady throttle it runs fine, but starts stuttering when I step on it.

So I'm wondering if O2 sensors could cause this and not give a check engine light or could it be the fuel pump?

Ken, that you?
;-)

Took me 3 years and more $ than I'd like to admit, but in the end, about $5 worth of pins and a hour or so took care of my misfire.
http://www.zr1.net/forum/showthread.php?t=10828
Bottom line is, did you or your mechanic use the Haibec method of checking the Ohms of the old resistors? And when you did so, did you stick the probe of the volt meter directly into the ECM plug?
I did and paid the price.
You can't believe how hard it was to find, but you can believe the difference it made.

TomC
"Crabs

[ZR-1Mikko]

It's has only about year old Accel injectors, MSD coils, MSD wires and I had never pulled the ECM connector until this issue came up. So I don't think there is anything wrong with the pins in the connector...

[kenthompson]

Ken, that you?
;-)



Nope, Mikko's still runs.....:cry:

[kenthompson]

Mikko,

if you need help, let me know.

KT

[ZR-1Mikko]

Thanks Ken!

I will probably try to check the O2 sensors tonight, but after that I'm pretty much out ideas...

[secondchance]

Thanks Ken!

I will probably try to check the O2 sensors tonight, but after that I'm pretty much out ideas...

I presume you checked injector resistance. Was this done when the car was cold? Hot? Both?

[ZR-1Mikko]

Yes. Injectors measure all about 15.3 cold and about 16.3 when hot

[tf95ZR1]

but starts stuttering when I step on it.

Hey, I wonder if now I/we can beat you at Spring Mountain?
:mrgreen:

PS Fuel Filter?

[ZR-1Mikko]

If I can get this thing running again I wont even care if you beat me :)

Fuel filter was changed 2 years ago. After reading "Crabs" story I'm very hesitant to just start throwing new parts at it.

[bdw18_123]

Have you tried another ECM? When I lent my ECM to Tom C so he could troubleshoot his issue, it made his car run with a misfire. My ECM was bad and I didn't even know it (my Z isn't running yet). He took it to Jeffvette and it did the same thing in his car. Maybe borrow someone's ZR-1 ECM and see if it helps at all?

[Demps]

Sure sounds like ignition. Were the coils' resistance checked while motor was hot? I wouldn't throw parts at it but check them hot as others have had problems with non- GM coils. Problems will not always show across the coil/ wire.

[Zr1 Destroyer]

This sounds like the problem I had a while back.....I checked evrything and also replaced coils, injectors, sensors, fuel filter and still had a crazy miss in it at about 2500 rpm's that would stop the car in its tracks.


Soooo, I have a good buddy that happen to have an extra DIS module laying around......I swapped it and my car screamed and the miss was long gone.



Good luck....:wave:

[ZR-1Mikko]

Thanks guys for the tips!

I may have just found something.
Turns out my fuel pressure shakes around 45 on idle and goes down as I raise the rpm's. If I remember correctly it should be around 55?

[ZR-1Mikko]

Hey Ken if you are out there I wanted to see if I would be able to borrow your ecm to check if that is my problem....

[kenthompson]

Hey Ken if you are out there I wanted to see if I would be able to borrow your ecm to check if that is my problem....

PM'd you back, but this still sounds like fuel. Relay?

Glad to help if I can.

KT

[kenthompson]

FYI, since Mikko hasn't gotten back to this yet (more why in a sec)

We swapped the ECM out of 1790, and using the chip that Mikko had, into his car. Didn't seem to help much. Car still has a slight hesitation off idle, and runs poorly (at least according to what I remember mine running like. I.e. rip your head off at the mash of the throttle in first gear)

I thought for sure the secondaries weren't opening. Curious part was that no error codes were being generated (at least no SES light was on, even intermittantly)

I took a flashlight and verified that the secondarys did in fact work by observing them through a rapid throttle acceleration (i.e. wacking the throttle hard enough to make them react), and both sides do work.

After swapping the ECM, and listening to the car as it ran through my neighborhood, I can distinctly hear a "lean" condition when he gets on it.

So, that starts to indicate fuel problems.

We hooked up a fuel pressure gauge and achieved 50 psi at KONEOFF. Running, the pressure dropped to 42 psi. At Key off, the pressure rapidly reduced to around 20 psi, indicating a possible injector not properly seating.

Pulled the primary fuel pump fuse, and the car started and ran temporarily with the pressure rapidly reducing from 50 psi to 10 psi before the engine stalled.

I'm guessing (and suggested to Mikko) that we change the fuel filter and see if that affects the car at all. He indicated that he had recently changed the fuel pumps out.

He was going to do that later this evening after he left my house.

I'll let him carry forward with this.

KT

[ZR-1Mikko]

So the fuel filter is changed and still the same problem! It ran just a little bit better, but the same studder is still there through all rpm's.

Also wanted to add to Ken's description, that when the engine is warm it doesn't idle the way it used to - and makes the fly wheel to make a lot of noise.

[ZR-1Mikko]

I'm thinking that it must be a bad injector...which would mean my 2years old Accel's would have failed on me :(

The way this issue came up was:
Drove the car one day in normal city driving in good weather. No issues at this time. Parked it outside for one night. This was a Vegas winter night, which are not very cold, but little bit chilly. Went to start the car the next morning and discovered this issue. In the beginning I was able to get the car run normal for little bit sometimes by luck, but recently the studder is there at all times.

I did ohm out the injectors and they all ohm out similar cold and hot...

[kenthompson]

But would that make the car have no power without turning on a service light?

The car runs like the secondaries aren't working, but I've confirmed that the actuators are indeed working.

That's why I keep thinking fuel to the secondaires (or all of them not firing), or ignition timing.

Mikko, I did notice last night that each time you fire the care, you get a knock. Maybe the knock sensor is getting flakey and retarding the timing?

KT

[Pete]

If it's not fuel.
Can i ask what spark plugs are you using and where did you gap them/

Pete

[ZR-1Mikko]

It has brand new stock Ac delco plugs which I believe had the correct gap right out of the box...

[Pete]

I never seen a/c delcos gapped from the factory.

Can you take a couple out and check the gap,easy and free

Pete

[ZR-1Mikko]

If it is a failing O2 sensor would it be possible that it wouldn't show any codes for it?

[Locobob]

If it is a failing O2 sensor would it be possible that it wouldn't show any codes for it?

Yes, at least to some degree. I've noticed a lot on these cars can go wrong without tripping a code.

[A26B]

If it is a failing O2 sensor would it be possible that it wouldn't show any codes for it?

One way to check is to drive with rpm higher than 3200 rpm, i.e. in open loop. If the miss disappears, it's likely the O2's. If an O2 fails, it will throw a code (or supposed to anyway) & will run like crap in closed loop.

I had water get into the RH O2 connector on a trip from Houston to OKC. Engine was about to shake out of the Zee until I got it into open loop. Drove it the last 150 miles just into open loop & made it home fine.

[ZR-1Mikko]

It definitely has a miss after 3200 rpm's. It must be a sensor of somekind. I think I just need to find connector to plug a computer to it...

[LT5-Lee]

In a regular situation on a common GM car, a knock sensor would be a logical choice after going through all the variables you exhausted.

I had such a problem a while back and traced it to a MAP sensor plug that looked and felt plugged in, but was not. It was so close it worked until the engines torque movement or rapid acceleration must have caused a disconnect on one terminal. From now on, I do not consider it connected until you hear a loud click when connecting it. It is a pain, but disconnecting & reconnecting all the terminals you can get too might pay off and make sure your grounds are in good shape. I plan on adding a few in the future just for grins.

[A26B]

It definitely has a miss after 3200 rpm's. It must be a sensor of somekind. I think I just need to find connector to plug a computer to it...

I think you have eliminated the O2 sensors.

As for the knock sensor, a bad sensor or lead will give you a SES light and prevent secondary operation.

I haven't read the whole thread, have you pulled codes, cleared and restablished codes?

[Demps]

Any chance for bad gas? Running Shell nitrogen gas successively?

[ZR-1Mikko]

ok I will try to list here what I have done so far:

Injectors -2years old Acccels with about 10k miles on them. I ohmed them out and they all had matching readings both hot and cold.

Coils - brand new MSD. I ohmed them out and they all had matching readings when cold. I did not ohm them out hot since they are new.

wires - 2years old MSD with 10k miles on them. I ohmed them out and they all had matching readings when cold.

Plugs - brand new Ac delco 41-602. The old ones that I took out after this issue came up were all the same color and condition, so it seems that it is not any specific cylinder having the problem...

O2 sensors - Changed out new one on one side and replaced the other side with the one that came off the side with the new one. Did this after I tested that the new one did not fix the issue.

Fuel pumps - Brand new Airtex with new strainers (these are the ones sold as replacement for LT-1)

Fuel filter - brand new and also drained some gas out of the tank to make sure there is no dirt left.

Fuel pressure - about 45lbs when engine running. With key on and engine off the pressure is leaking a little bit, which Ken thought that might be a leaking injector.

Secondaries - We were able to see the actuator arms moving when stepping on the gas

ECM - tried one off Ken's 1990 and it did not fix the problem

And then the current syptoms:
When cold the car iddles fine right after start, but starts to randomly miss about 2 minutes after start. (It might have the miss right off the start, but I can't really hear it since the air pump is running)
When taking off cold the car studders the same was as it does when hot. I can feel the studder on all rpm's hot and cold. The only time I don't feel it is when I'm moving at steady speed with a steady throthle around 1500-2000rpm.
And just to be clear the car does not pull the way it is supposed to...

So at this point I'm out of tricks, energy and ideas ::dontknow:

[Dynomite]

Mikko, if you are having a rapid fuel pressure loss, you have an injector that is bad, or one that is possibly grounded open and draining the fuel.

You can pull the plenum and dislodge the fuel rails. Lay some shop rags or heavy duty paper towels underneath the injector tips and then prime them, and see what is leaking.

But definitely check your injector wire harness to see if you have crushed one of the wires.

Did you try Jeffvette suggestion above :dontknow:

I had almost zero compression on one cylinder with one secondary injector having very low resistance and did not have as severe symptoms as you are having :mrgreen:

This is very interesting :neutral:

[Demps]

Personally not a fan of non-GM coils. Others have fought that--guy on this board from OK.

What is the plug gap?

Are you sure the ignition module connector is tight?

Wish I were there to help. Should be there in 3 weeks if it is still acting up.
Car will go closed loop about your trouble time. My O2 symptom was passing 126F water temp it stumbled then would correct itself.

[ZR-1Mikko]

It really can't be the wire harness, since the problem came up overnight without touching anything in the car.

Now if it was just one injector bad wouldn't I be able to see that on the plug?

I will check all the connectors one more time tomorrow....

[Zr1 Destroyer]

DIS mod......

[ZR-1Mikko]

I have not checked the dis mod yet...

Did check all the connections the other day and no success... :(

[ZR-1Mikko]

before I pull the plenum one more time I have couple things I'm wondering if anyone would happen to have answers for?

So if I pull the injectors to check for leaks can I just connect the battery and turn the power on from the key to prime them or what would be another way to prime them?

Is it possible to ohm out the Dis module to see if it is failing? Or should I just borrow someones Dis and swap it?

[Demps]

before I pull the plenum one more time I have couple things I'm wondering if anyone would happen to have answers for?

So if I pull the injectors to check for leaks can I just connect the battery and turn the power on from the key to prime them or what would be another way to prime them?

Is it possible to ohm out the Dis module to see if it is failing? Or should I just borrow someones Dis and swap it?

Small tab connector on wire bundle going into ECM is fuel pump test--jumping to + on battery will run fuel pump and pressurize rail.

DIS is not testable without a specialty test set (I would imagine).

[ZR-1Mikko]

Thanks for the tips!

[tccrab]

before I pull the plenum one more time I have couple things I'm wondering if anyone would happen to have answers for?

So if I pull the injectors to check for leaks can I just connect the battery and turn the power on from the key to prime them or what would be another way to prime them?

Is it possible to ohm out the Dis module to see if it is failing? Or should I just borrow someones Dis and swap it?

With the plenum off you can pressurize the fuel rails and actually fire individual fuel injectors and see them squirting fuel.
With the battery disconnected, pull the yellow plug out of the ECM. This the one closest to the outside of the car.
There are 24 pins in the plug, 4 rows of 6.
Put the battery cables back on and turn the ignition key to the 'ON' position.
The fuel rail is now pumped up.
Using the following chart (is for '90 - 91's, others are slightly different) to determine which pin in the yellow plug goes to which fuel injector. For example, Fuel Injector 1 for cylinder 1 is Y1, position 1 in the first row of the yellow plug.
All you need to do to fire fuel injector for cylinder 1 is apply a good ground to pin Y1 and looking down the appropriate injector housing hole you can visually see the injector squirt fuel on top of the valve.
Use a very thin wire, nothing larger than a small paperclip.
DO NOT, I repeat, DO NOT use anything that is larger than the male pin on the ECM itself to ground out this circuit.
If you stretch the female pin inside the plug with too large a wire it will FUBAR the connection and it could take you YEARS and $$$ to figure it out and fix it!!!
(don't ask me how I know this, just accept it to be fact.):rolleyes::mad::redface:

http://i71.photobucket.com/albums/i159/tccrab/ZR1_Primary_Injectors.jpg

Tom

[ZR-1Mikko]

so i finally got around to pull the plenum again and went to try to fire each injector individually from the yellow ecm connector and nothing happened. No fuel pressure and obviously no fuel from injectors. So I went and connected the yellow ecm connector back and was able to get the fuel pressure when I turned the key on. Looking down to the injector housings's none of them are leaking... How ever the fuel pressure goes up to about 30 lbs and starts coming down slowly right after I turn the power on. The car has new fuel pumps and fuel filter, so I don't see those being the problem. Talking to couple people we are wondering if it could be the Fuel pressure regulator leaking and causing the issues I have been having with the car?

I guess there is no way of checking if the regulator is bad? I just hate go buy a $200 part without knowing for sure...

[tomtom72]

so i finally got around to pull the plenum again and went to try to fire each injector individually from the yellow ecm connector and nothing happened. No fuel pressure and obviously no fuel from injectors. So I went and connected the yellow ecm connector back and was able to get the fuel pressure when I turned the key on. Looking down to the injector housings's none of them are leaking... How ever the fuel pressure goes up to about 30 lbs and starts coming down slowly right after I turn the power on. The car has new fuel pumps and fuel filter, so I don't see those being the problem. Talking to couple people we are wondering if it could be the Fuel pressure regulator leaking and causing the issues I have been having with the car?

I guess there is no way of checking if the regulator is bad? I just hate go buy a $200 part without knowing for sure...

There is a procedure in the FSM for checking the regulator. Also, pull the regulator vacuum hose off of the plenum connection and see if there is gas in that hose, gas in hose = regulator N/G. Obviously make sure the hose is not collapsing under engine vacuum.

In the "driveability and Emissions" section chart A-7 has a two page diagnostic for the fuel system. Pages 6E3-A-28 is where it starts. Sorry my office phone rang...work interferes all the time. You may want to look over that chart and maybe look in the "Intermittents" section, 6E3-B-1. I know if you slowly pinch the return hose the FP should go up, and if you pincgh off the fuel feed line the pressure should hold. But those are only small parts of the entire diagnostic chart. I wish I kne enough to say you diodn't have to run the entire chart....but I'm afraid that I don't. Sorry.

[Jeffvette]

so i finally got around to pull the plenum again and went to try to fire each injector individually from the yellow ecm connector and nothing happened. No fuel pressure and obviously no fuel from injectors. So I went and connected the yellow ecm connector back and was able to get the fuel pressure when I turned the key on. Looking down to the injector housings's none of them are leaking... How ever the fuel pressure goes up to about 30 lbs and starts coming down slowly right after I turn the power on. The car has new fuel pumps and fuel filter, so I don't see those being the problem. Talking to couple people we are wondering if it could be the Fuel pressure regulator leaking and causing the issues I have been having with the car?

I guess there is no way of checking if the regulator is bad? I just hate go buy a $200 part without knowing for sure...


Mikko, if you need a regulator to check, I have one. I'll ship it to you, if it works pay then. If not return it.

The manual has a pretty good diag of this, and it is fairly simple to follow along. But I am thinking it is not the regulator, but maybe a checkvalve on the fuel pump. The section you need to be in is 6E3 Section A. There is a fuel System Diagnosis chart.

[ZR-1Mikko]

Thanks guys. I found the chart. Will be doing the diagnosis tonight and let you know what I find.

[ZR-1Mikko]

Well I'm officially going crazy with this thing.

After following the fuel system diagnostic chart I came to a conclusion that the injectors are leaking. How ever after testing the injectors like Jeff suggested I was not able to see any gas leaking from the tips of the injectors. So I just can't figure out what am I missing here... I can not find any gas leaking anywhere...
The only thing I'm did different from manual is that the plenum was off when I did the test. But that shouldn't affect the test should it?

I think someone is trying to tell me I'm not meant to work on this car and just drop it at local shop to see what they can get out of it...
Unless one of you guys want a round trip to Vegas and give it a try:dancing

[XfireZ51]

Well I'm officially going crazy with this thing.

After following the fuel system diagnostic chart I came to a conclusion that the injectors are leaking. How ever after testing the injectors like Jeff suggested I was not able to see any gas leaking from the tips of the injectors. So I just can't figure out what am I missing here... I can not find any gas leaking anywhere...
The only thing I'm did different from manual is that the plenum was off when I did the test. But that shouldn't affect the test should it?

I think someone is trying to tell me I'm not meant to work on this car and just drop it at local shop to see what they can get out of it...
Unless one of you guys want a round trip to Vegas and give it a try:dancing

You might talk Ccmano to drive his 90 out to see you from LA!

[tccrab]

Since you've already got the plenum off, I'd yank the injectors and take them someplace to be flowed.
You never know, you could have a bad one or two.

TomC
'Crabs

[tomtom72]

:o Not to be a wise a$$ Mikko.....when you checked the injectors did you put a paper towel or tissue under them or did you just do it by eye?

I'm only saying that when ever I do anything on my fuel system, like R&R the filter I use a tissue at the connections to check for leaks. Found a slightly worn O-ring that way last weekend.

Okay, barring any leaks the results say injector leak....what do the plugs say? Also, I agree with TomC that maybe a flow/leak test is in order......If you are positive ( again not trying to be a wise guy ) your run thru chart A7 had no mistakes on your part.:o I do that alot, make mistakes using the charts.

:cheers:
Tom

I just had a BFO.....I remember another write up about a mystery miss that turned out to be one of the metal pipes on the in-tank pump/sender assembly having a hair line crack in the tubing. Sorry I didn't think of this sooner.

[Paul Workman]

Initially, the suggestions were in line with what I might have suggested, so I kept quiet to see what the results were. But, after reading the thread, a couple things come out which may be more the result of putting stuff in writing, so take this with a grain of salt, if I'm off base:

Troubleshooting: One of the deadliest traps one can get into is to assume something or another can't be the problem because it was recently replaced with a new item. I read this several times in this thread, and so I raise it as a flaw in the logic. A technique that has saved my bacon many times is to assume NOTHING about the condition of a device is known unless it is tested!! You might be well served to step back and then proceed to test functionality of components in question and forget about when it/they were replaced. (In fact, one of my new - out of the box - Airtex fuel pumps had bad check valve resulting in a failed leak-down test. I had to isolate the pump to determine the problem (more on that later, if you want - got pictures showing how that is done).)

The other is putting a scanner on it or a computer and data logging to see what is going on. Problems leading me to buying my own scanner stemmed from "no codes thrown" condition, yet ran like chit (and a "no problem found" from the dealer's mechanic) In one case one of the O2's was shorting out after reaching about 3000 rpm, but it wouldn't do it all the time. Try to run THAT down without a scanner! My point is, a scanner and data logging will show you what is really going on over 40 some sensor and readout results and time stamp them all so you can see the interaction.

Hope this doesn't sound "preachy". Just that I'm late for work - gotta run!!

Mo later if ya need.


P.

[XfireZ51]

"The other is putting a scanner on it or a computer and data logging to see what is going on. *Problems leading me to buying my own scanner stemmed from "no codes thrown" condition, yet ran like chit (and a "no problem found" from the dealer's mechanic) *In one case one of the O2's was shorting out after reaching about 3000 rpm, but it wouldn't do it all the time. *Try to run THAT down without a scanner! *My point is, a scanner and data logging will show you what is really going on over 40 some sensor and readout results and time stamp them all so you can see the interaction."

Can't emphasize this point more.

[ZR-1Mikko]

Well the search has finally ended and I want to thank everyone for their input and especially Ken for letting me borrow some parts...

Before I go to details I have to say that Paul is absolutely right about to NEVER assume something or another can't be the problem because it was recently replaced with a new item!

So after having my friend mechanic look at the car the end diagnose is that the car had two issues. The main cause for the miss was a failed spark plug wire! My self the only thing I did to the wires was to ohm them out, but since they were only two years old MSD wires I never spend a lot of time inspecting or trying out my old wires which I obviously should have done.

The second issue was the hoses connected to the fuel pump assembly in the tank were loose. It seems very unusual, but the clamps were loose causing a poor fool pressure.

So after 6 month break another ZR-1 is back on the road :-D

[tccrab]

Fantastic!!!

Now get in it and drive it like you stole it!!

Personally speaking, I guessing that I probably would have eventually found the bad plug wire given plenty of time and stress.
But I don't think there's any chance in he!! that I'd have found the loose fuel hose clamps.
My hat is off to your mechanic buddy, he's a keeper!!

TomC
'Crabs

[Hammer]

:cheers:

[tomtom72]

glad you got to the bottom of the trouble!:thumbsup:

Now go drive her....you both deserve it! :mrgreen: