Runs great then randomly shuts off

Tiny
JSHAW94
  • MEMBER
  • 1994 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 256,000 MILES
Truck listed above is the 2500. Replaced plugs, plug wires, and coil. Runs great for a while then randomly shuts off. Starts but will not stay started. Apply a little gas while starting and will run but runs rough until about 3,000 rpm's. Random stalling running but doesn't completely stall out. Kind of like a major misfire.
Thursday, June 11th, 2020 AT 11:26 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

This could be related to fuel pressure, a faulty crankshaft position sensor, and so on. Do me a favor. I need you to retrieve diagnostic trouble codes. That should point us in the right direction. This truck has an OBD1 system and doesn't require a scan tool. All you need is a short jumper wire or even a paper clip.

Here is a link that explains how to do it:

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

Do this and let me know what you find. Hopefully it points us in the right direction. Also, let me know if this only happens when the truck is warm.

Take care,
Joe
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Thursday, June 11th, 2020 AT 9:39 PM
Tiny
JSHAW94
  • MEMBER
  • 3 POSTS
Thanks for responding. Okay, I ran the code and it came up 34 MAP sensor. Replaced MAP sensor and it fixed that problem. But once that problem was fixed it now reads a 22 code. It idles now at 1,200 rpm's. I unplugged the TPS and it stays the same. Took TPS off and stays the same. I just ordered a new TPS from Amazon. But the intermittent stutter and random problem doesn't exist as of yet.
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Friday, June 12th, 2020 AT 1:55 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Check the wiring and the connector at the TPS. The code 22 indicates low voltage. Normally it would be checked with a scan tool, but you can try checking voltage with a multi meter or volt meter. At an idle, voltage at the TPS should be between 0.5 to 1.25V. It should increase as you press the throttle to increase RPM's.

Let me know if the new TPS helps or if the code returns.

Take care,
Joe
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Friday, June 12th, 2020 AT 11:13 PM
Tiny
JSHAW94
  • MEMBER
  • 3 POSTS
Checked everything. Found no problems. I decided to then just randomly check the IAC. Took it off again and really cleaned it up. For some reason I looked inside the plug. That's when one of the wires broke. So I replaced the plug end. Problem solved. No codes no stutter. Runs more smooth than it has in a long time.
I really appreciate you taking the time to help. I have an obd2 scanner but not a obd1. That was major help. Again thank you.

Take care.
Justin
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Saturday, June 13th, 2020 AT 9:53 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Justin,

You are very welcome. I'm glad to hear it's fixed. Take care of yourself and let us know if you have questions in the future.

Joe
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Saturday, June 13th, 2020 AT 7:45 PM

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