Hello.

I have a convertible camaro 305 TBI 1989 since 18 years now. I meet a problem with the engine.

It runs well, except, since a few time. When I start it, it runs, and randomly stall. Sometimes, after just 30 seconds, or after 1 or 2 minutes. It restarts immediately and runs for a while, for 30 s, 1 or 2 minutes or more, and stall. And again….It does it, until it is well hot, and sometimes, even a operating temperature stall again. When the car is hot, since a few minutes, it doesn’t stall anymore and runs very well.

When it stalls, it stalls like if I switch off the ignition, without any sign before. I tried to increase the rpm, to avoid to stall, but even keeping it at 2500 rpm, it stall the same way, suddenly. When the temperature is at 95 C° for a few minutes, the problem disappears, and it doesn’t stall anymore.

What I have done :

-checked the fuel pressure and the flow : 12 psi and 1 pint and a half in 15 s (shop manual give 9 to 12 psi and 1 pint in 15 s). So it’s OK. I stayed looking at the fuel pressure (I installed one in line) when the engine runs, and when he stalls, the fuel pressure is at 12 psi without failing, and pressure decreased 1 or 2 s AFTER it’s stalled, like it has too. I also open the tank to be sure to not have a vacuum problem in the tank. So I’m sure that it’s not a fuel feeding problem.

_I changed the ICM and the coil (but not the pick up coil I forgot to order it with the others parts) ; if it was the pick coil, would it give a random problem and the engine would start at cold? )

_ I checked all the sensors with my computer and WinALDL program. All the values are in the good range, even when the engine is running, and when it stalls, I didn’t notice something becoming wrong.

- There is no error code (I founded one (N°42) but it was the ecm connector not full seated. Now, no more error code.

So, now, I don’t know where to search to identify the problem . I am from France, and far from any American car garage (rare) who could help me. Is someone would have an idea and help me were to search ? I'm afraid to use my car and to stall in the middle of the traffic and to not be able to restart the engine.
Thank you for your help.

Jean Luc

 

It's very tough to diagnose such an intermittent problem. It no different being an American car than any other car.
Seems like you have a good knowledge of what you are doing, you've checked things I would have looked at. Since you say it seems electrical, check and clean all powers and ground straps. There's a couple grounds that go between the engine and the chassis, make sure to check those. Examine the wiring around the ignition. Check to see if you are losing power to the coil when it dies. Possible problem with the wiring coming from the ignition switch at the bottom of the steering column, or the switch itself.

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I have had an Eerily similar experiance .
I replaced spark plugs, cap and rotor, coil,spark plug wires, battery etc.....car would start right up and sounded strong upon cold start. Let me spare you the emotional roller coaster ride of my story and get to the good part. The fix!!! Wiggled every single wire
/pin coming off the ECU and found a short.
The wire would disconnect and cause a short as the car got warm but ran fine cold.

Replaced the wire and that solved the infamous stumbling , Stuttering idle and cutting off in traffic. Please check your connections for frayed wires and bad contacts. I hope this helps you resolve your issue in some shape form or fashion.
Good luck and keep us updated.

 

Thank you for your answer. I'll try the grounds this week. I found an interesting way to check the grounds. I put the photo which explain the way to do. A friend of mine who is an industrial electritian know this method and told me that is a good way to do. I'll try to put a parallel light on the 12 v feed of the coil, to see if the light switch off when the engine stall or not. This will avoid or not a problem with the ignition switch or anti theft system. I'll tell you the results. I'll tell you the results.
Jean Luc

 

Thank you to share with me your experience and how you fixed it . I inspected the harness of the ECM when I disconnected it. I didn't see something wrong, but didn't checked every pin to see if one of them could coming off. So I'll check it again deeper. I'm sure that it's a stupid failure in that style, or bad contact somewhere. But the problem is to find where it is.... I'll tell you the control I do and the results as the things progress.
Jean Luc

 

Hi.
As I told you, I tried this week to find what is the problem on my Camaro. I checked the wires to find frayed ones and harness to find pins coming off. All seems OK.
I checked all the engines, ECM, 02, TPS etc.. grounds with the method with volt meter (see the sheet voltage drop test upper). The worse ground was 0.075 V, and the better one was 0.03. As they need to be around 0.1 V, all is OK from this side. I checked all the vacuum hose, without seeing anything wrong.

I founded something weird with the software WinAldl. All the values of the sensors are in the correct range when the engine run. But I recorded the data, and when I checked the record, I saw that the data from the tps change from very important values (60 or more) and can even drop at 19, the engine idling and without touching the throttle, and that the sensor voltage don't change (normal I don't touch the throttle). Only the TPS data make ups and downs. So I wonder if the problem would be the ECM.

Otherwise, how explain the changes of data when they shouldn't change, because idle is manage by the IAC? If someone has an idea.... If founded too knocks when idling, when it should not have. I'll check the timing and ESC, but I don't think this problem could shut off the engine. Just something to adjust.
Next steps, will be to check too if the coil has power when the engine stall, and a complete checking of all the ignition system with the shop manual (many things to do). And to heat the ECM to see if when it's hot, and the engine cold, it's stall or not. If so, it could be bad welding in the ECM. As you see, I have yet a lot of work to do.....
So I hope I will be able to find where is the problem. Not an easy task.....
I'll tell you news soon, Now I take some holidays. It need it, the car makes me nuts...

 

the tps reading moving when the throttle isn't being moved is concerning. You can use a voltage meter to verify that at the tps with the engine off and key on. If the meter is a good meter you can usually see the sweep of voltage stay gradual and not jump around. You might want to resistance check those wires too if you don't find a problem at the sensor. Something to repair even if it doesn't fix the problem.
You'll find it. You seem pretty smart and diligent.

 

Thanks for your advice. I'll try it and tell you soon.
Jean Luc

 

Hello.
I came back to work on my car. I tested the TPS like you told me, without finding anything. It runs well. I checked the positive feed of the coil with this method:

I made a mounting with a relay and a light test to see if the feed cuts when the engine stall. The advantage to use a relay with the schema I join, is that if the positive feed cut (even quickly) and come back, the light test switch off but can't switch on alone. You must trigger again the mounting. Like this you are sure that they is no cut off the feeding if the light test stay on. When you start the engine, you have to trigger the mounting to "arm" it. The light switch on and "watch" the feeding. This method helped me to see that they is no cut when the engine stall, and that they is no problem with the positive feeding of the coil, and no problem with the ignition switch on the steering wheel. (see the schema and photos of the Pin I putted in the feeding wire to go to the relay and the schema to know were is the good wire at the coil (hope this will help someone).
I cleaned all the contacts of sensors, and ECM harness with a professional electric contact cleaner. But doing this, I made a mistake. I put a "good " amount of cleaner on the HEI module pins. Blowed it and connected it again. When I switched on the ignition, I tested the ground of the HEI and feel the plate under the HEI very hot, too hot to be able to let the finger on it. In fact, I didn't see that the pins are not seal in the HEI. The cleaner went inside the HEI and probably made a short cut. I had another HEI so I changed it and it's now ok. (Sometime, trying to do the best is the enemy of the good )
I checked and cleaned the ground of the HEI (it was not perfect), and cleaned all the grounds of the body and engine, and the positive connectors at the battery. All are so much cleaned that they seems in silver .
This morning I started the engine in my garage and let it go to 90 C°. It didn't stall. But this morning here was not cold (22 C°). So tomorrow, I'll try it again, and if it runs well, I'll go to drive it.
At this day, I didn't find something really wrong. Was it the HEI module (I changed it 3 months ago), positives and grounds not very perfect but not bad, or others contacts cleaned by the electric cleaner? I don't know. I hope the car will run well now, I'll see it pretty soon . I'll tell you.......

 

Good work. Hopefully it stays working well for you. Thank you for the follow up.