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Stalls coming to a stop when engine is warm

Tiny
HOCKEY0420
  • MEMBER
  • 1988 GMC S15
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 350,000 MILES
On cold starts my engine will run great until it gets warm and I am coming to a stop, even on left turns, the engine will idle down so low it shuts off. I am able to start right back up most times and I will have to keep my foot on the gas to keep the engine running. If it does not start back up right away, I have to unplug the injectors and start the truck to run the gas out in the carburetor, re-plug in the injectors and give it gas when I restart again. The truck runs great on the freeway and most of the time I can get from place to place without it shutting off. My main problem is driving around town with stop signs, stop lights.
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Thursday, July 5th, 2018 AT 3:58 PM

16 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
Hi and thanks for using 2CarPros.com.

Based on your description, it sounds like the fuel pressure is too high. First, I would recommend checking pressure. I have attached a picture which contains the manufacturer's specifications for pressure.

Here are general directions for checking pump pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The picture I attached has more specific directions. The second picture shows the regulator. To the best of my knowledge, and the research I have just done, there are two different throttle body injection systems for this vehicle. One is a model 200 and the other, 700. The model 200 has two injectors and a built in pressure regulator. The 700 has one injector and a serviceable regulator.

Now, at this point, I have a feeling that you will find the pressure to be higher than it should be. Often times the fuel pressure regulator goes bad. The result can be pressure which is too high or too low. Since you have to unplug the injector and start the engine, it leads me to believe it is too high.

Check this first and let me know what you find or if you have other questions.

Take care,
Joe
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Friday, July 6th, 2018 AT 8:25 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
Something happened and the pressure did not go through when I replied. Trying again.
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Friday, July 6th, 2018 AT 8:31 PM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
Okay, thank you. It will take me a week to get a gauge. I will let you know when I test that. I have taken the regulator apart and the diaphragm is fine, my truck is the 200 model. This problem has been intermittent like I can drive to the store fine and on the way back it struggles, if I get on the freeway on my way back from my last stop it drives fine. It has been happening since I got the truck in march. Is there any sensors or vacuum lines I might have looked over? It is kind of tough to know which lines goes where because this truck has clearly been worked on before by an amateur.
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Saturday, July 7th, 2018 AT 12:00 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
Hi, and you are welcome. I hope it helps. I did not ask before, but have you checked for trouble codes? This has the OBD1 system, and it may have a trouble code stored which will be very helpful in diagnosing the problem. This is something you can do at home very easily. All you need is a paper clip. Follow the directions on this link and tell me what code you find, if any.

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Let me know what you find,
Joe
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Saturday, July 7th, 2018 AT 8:05 PM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
I have checked for engine codes and nothing shows up. It just keeps flashing code 12.
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Saturday, July 7th, 2018 AT 11:20 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
Welcome back.

A code 12 can have two different meanings for GM OBD1 systems. First and most commonly, it indicates that a diagnostic test is active. If a hard code 12 is set, that indicates a reference issue between the computer and the distributor. In that case, the engine would not run and your's does, so in this case I feel it is safe to say it is the code for the diagnostic test active.

Lets try the original plan with fuel pressure/regulator. Let me know what you find.

Joe
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Tuesday, July 10th, 2018 AT 5:52 PM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
On my way home from work last night and my truck shut off while I was at speed on the freeway. I lost power and pumped the gas a few times with no response, so I pulled over tried to restart and nothing. I pulled the injector plugs off and turned the engine over, plugged them back in started the engine and I had to step on the gas to keep it on. About a mile or two down the road it shut off again and this time I heard some backfiring when I pumped the gas trying to get a response. I know I do not have a fuel issue now. The ignition coil was replaced maybe a month or two ago and it looked like the spark plug wires were changed when I bought the truck in March. Would a bad catalytic converter cause this? What would be my next step? Oh, and I checked engine codes and it flashed code 12 three times then code 3. I was trying to find some information on code 3 and found nothing.
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Tuesday, July 17th, 2018 AT 3:18 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
This sounds like the fuel pump is going bad or one of the injectros is shorting out causing the PCM to go full ON with the injector pulse. This can be hard to detect because the short intermittent and will test okay most of the time.

But you never know. Here is a guide to help you see whats going on:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Please run down this guide and report back.

Cheers, Ken
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Saturday, July 21st, 2018 AT 1:52 PM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
My truck will not start now. I checked fuel pressure a few days ago and that was at 13-14 psi. I know fuel is getting to the cylinders but it is not sparking. I just replaced the distributor, ignition coil and I know I am getting power through the ignition coil. The truck was running decent just felt like it needed to be timed. Now it is not running at all. I think it is some electrical issue but I do not know how to trace it down.
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Saturday, July 21st, 2018 AT 4:37 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
When you replaced the distributor did you do the ignition module? They go out all the time here is diagram to show you how.

Check out the diagrams (below). Please let us know what happens.

Cheers, Ken
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Sunday, July 22nd, 2018 AT 11:47 AM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
Yes, it was the ignition module that messed up the distributor and I also had a buddy come by with a scanner to read what is going on with the truck and everything on the ECM was working properly. So the truck starts now, then I noticed one of the injectors was not spray it was dripping more then anything especially when I stepped on it. I replaced the injector and now it seems like the temperature takes forever to reach "operating temperature" and it runs badly. It idles okay, but when I step on it I get a response and immediately loses power, does not shut off but no acceleration, I have to floor it to get it to move. It does a little better when the temperature gauge is around 200 (operating temperature on my gauge) but still not perfect. Do you think the ECM temperature gauge is bad and it is making my cluster temperature gauge show different readings. I changed the ECM temperature gauge probably four months ago and it has been working fine. Maybe I should just change both? I do not know, what do you guys think?

Thank you for all your guys help so far it has been easier for me to find the problems.
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Monday, July 30th, 2018 AT 9:44 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
It sounds like the thermostat is stuck open or is missing which will cause all kinds of computer issues. Please remove the thermostat to check. Here is a guide to help:

https://www.2carpros.com/articles/replace-thermostat

Check out the diagrams (below). Please let us know what you find.

Cheers, Ken
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Tuesday, July 31st, 2018 AT 11:22 AM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
I changed the thermostat and had no change. Now the temperature gauge is not working and it looks like it is leaking from the water pump. I am going to change the water pump and thermostat sensor tomorrow. Is there anything else that would cause this? Maybe a vacuum sensor or something? The truck still does not accelerate properly.
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Saturday, August 4th, 2018 AT 4:56 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Yes, do the water pump and coolant sensor. Here is a guide that will give you a step by step on how to do it:

https://www.2carpros.com/articles/water-pump-replacement

and

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Please run down these guides and report back.
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Sunday, August 5th, 2018 AT 3:34 PM
Tiny
HOCKEY0420
  • MEMBER
  • 8 POSTS
I have replaced the whole cooling system now and it is doing the same thing, absolutely no change.
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Thursday, August 9th, 2018 AT 8:57 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
The tough part about obd1 is you cannot read the values so it is a bit of a parts shoot. It sounds like when the PCM gets warm it can control the engine. Let run down this guide next.

https://www.2carpros.com/articles/stall-at-idle

Go over this and do some checks and get back to me. Ken
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Friday, August 10th, 2018 AT 10:37 AM

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