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Engine starts chugging and will stall out

Tiny
TRUBLUROOKIE
  • MEMBER
  • 1993 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 265,000 MILES
When I start the truck cold everything is fine. Once the truck warms up and the RPM's drop the truck starts chugging and the truck will stall out and die. While driving and pushing on the gas everything is fine it only stalls at stops signs or when the truck is warm and idling. I have replaced the O2 sensor, and Idle air control valve. I also checked the fuel filter and it seems fine. I'm out of ideas!
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Tuesday, May 26th, 2020 AT 9:18 PM

71 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,896 POSTS
Hi,

This could be a few things. The engine coolant temperature sensor can cause this, an engine vacuum leak and so on. I want to start by checking for diagnostic trouble codes so we aren't guessing.

Here is a link that explains how to retrieve codes. This has an OBD1 system and it doesn't require a scan tool to check. All that is needed is a short jumper wire or even a paper clip. Follow this link and let me know the results.

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

and

https://www.2carpros.com/articles/engine-stalls

Let me know.

Joe
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Tuesday, May 26th, 2020 AT 9:30 PM
Tiny
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I'm not showing any error codes.
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Wednesday, May 27th, 2020 AT 12:23 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Check to see if there are any vacuum leaks. Here is a link that explains how it is done. Also, if there are no leaks, we will need to make sure the catalytic converter isn't partially plugged and causing issues at idle when warm. You could remove the O2 sensor before the cat to see if that makes a difference.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

One other question. When this happens, if you place it in neutral, does the idle return to normal or will it still stall?

Let me know what you find.

Joe
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Thursday, May 28th, 2020 AT 8:31 PM
Tiny
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  • 48 POSTS
The O2 sensor before that catalytic converter was the one I replaced. Can I just unplug it to test it or do I need to take it out? Also, the truck will stall and shut off in neutral or in gear. If I'm not pressing on the gas it will shut off.
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Friday, May 29th, 2020 AT 7:04 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,896 POSTS
Hi.

Remove it so there is an additional location for the exhaust to vent from. This will reduce back pressure if the converter is plugged. Simply because of the size of the sensor port being small, it won't make things perfect. However, if the converter is the issue, you should be able to tell a difference.

Let me know.

Joe
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Friday, May 29th, 2020 AT 9:29 AM
Tiny
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I did find a broken boot on the vacuum tube that goes to the PCV valve. I replaced it and it didn't fix the issue. I was reading the directions in the link and where is the throttle bore gasket? If it makes any difference I can smell the exhaust much more like the truck is running rich.
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Friday, May 29th, 2020 AT 12:03 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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The throttle bore gasket, it is between the throttle bore an the intake. See pic 1.

If the gasket is leaking, that would create a lean mixture. The idea that you smell fuel would indicate a rich fuel mixture. Have you checked fuel pump pressure to see if it is high?

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

Let me know.
Joe
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Friday, May 29th, 2020 AT 6:38 PM
Tiny
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The fuel filter and pump were one thing I thought about. I got a pressure test kit and a new fuel filter. I will test the pressure and replace the fuel filter tomorrow. Also I have read some about maybe the distributor causing this issue?
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Friday, May 29th, 2020 AT 8:13 PM
Tiny
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It could be related to the ignition control module. If it is failing, it can cause issues with both ignition and injection timing.
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Friday, May 29th, 2020 AT 8:33 PM
Tiny
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Okay, I once I started messing with the distributor I noticed the cap was full of carbon and the magnets were covered in rust. I replaced the distributor and it runs great. It is still missing a little bit tho. Will the truck computer catch up and work it out or do I still need to replace something else?
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Tuesday, June 2nd, 2020 AT 4:01 PM
Tiny
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  • MECHANIC
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The computer may be going through a relearn process. If it continues, see if you can find codes.

Let me know, and I'm glad to hear it's going for you.

Take care,
Joe
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Tuesday, June 2nd, 2020 AT 8:13 PM
Tiny
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Also, when I first start my truck it idles pretty high and doesn't go down once it's warmed up but once I put it in gear and start driving it will settle to a normal idle rpm. Could this also be a computer relearning issue too?
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Wednesday, June 3rd, 2020 AT 4:26 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Absolutely. How many miles have you put on it since it has been running? It honestly shouldn't take too long for the relearn to happen.

Joe
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Wednesday, June 3rd, 2020 AT 8:39 PM
Tiny
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Maybe 6 miles.
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Thursday, June 4th, 2020 AT 10:03 AM
Tiny
JACOBANDNICKOLAS
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Okay. Drive it more. In addition to miles, speed, times started, and so on all play a part in the relearn. Try it for a couple days and let me know if it doesn't change.

Take care,
Joe
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Thursday, June 4th, 2020 AT 8:48 PM
Tiny
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I took it out today and got it up to highway speeds. It chugged some when I first started it but it seemed to fix itself. The truck ran great but I got a "service engine soon" light. I checked the code and it was 32 and saw it was the EGR valve. I had that same code once before and the next time I drove it it went away. Seems to only come on when I go at highway speeds.
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Friday, June 5th, 2020 AT 10:47 AM
Tiny
JACOBANDNICKOLAS
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You may have an issue with the EGR hanging up or even a vacuum issue. Have you done any work on it? Let me know that and if you have an electric shift transmission or not. See pic 1.

Joe
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Friday, June 5th, 2020 AT 9:51 PM
Tiny
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I have not done any work on the EGR but I did pull a lot of the vacuum lines off to inspect them and make sure they were okay when trying to fix the other issue. I don't know how to find out if I have an electric shift transmission.
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Saturday, June 6th, 2020 AT 12:45 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I'm Danny.

Just here to add my 2 cents. I've attached a picture of the location of the EGR valve and cleaning instructions if this helps. I've owned a few 88-98 K1500's. The EGR is behind the throttle body near firewall. If it's too far gone you can replace. As far as your transmission it is more likely to be the 700R4 which is non-electronic. We can confirm with your VIN - the vehicle identification number. Attached my K1500's below. Hope this helps and thanks again for using 2CarPros.
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Saturday, June 6th, 2020 AT 11:20 PM
Tiny
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I know from past, and present transmission issues, that my transmission is a 4L60E. I will also get on with cleaning my EGR valve. Thank you
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Sunday, June 7th, 2020 AT 3:01 AM

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