1995 Chevy Silverado runs very rough, shuts off in gear

Tiny
MRODONATA
  • MEMBER
  • 1995 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
I have a 1995 Silverado - 2500 (3/4 ton) 4x4 with a 454 (7.4 liter) engine and I just replaced the (automatic) transmission this spring. Since I've gotten the truck back with the new transmission, it has been running terrible - RPMs all over the place, 'coughing', sometimes backfiring... And it dies or stalls almost every time I'm at a stop light or when the wheels stop moving - I need to use two feet (brake & gas) to keep it running at a light.

The 'check engine' light has been on (but it has been since I bough the car [used] a year and a half ago after my previous Silverado was totaled when I was rear-ended by an SUV - but that's another story.)... The codes I've checked since trying to diagnose this running problem indicated the EGR valve and MAP sensor - both of which I've replaced - and neither of which has solved the problem. We also checked the coolant temperature sensor - unplugging/bypassing it seemed to solve the running/idling problem - replaced this [relatively inexpensive part], but again, no fix. I've also replaced the fuel filter and ignition module (more recently it's been giving an 'ignition system' code) - neither of which have solved the problem either.

I've tried all of these:

EGR valve
MAP sensor
coolant temperature sensor
fuel filter
ignition module
premium/hi-octane gas

none of them have solved my problem.

What can be wrong with my truck? Might I have been the victim of sabotage? (Strangely, not long after the running problem started, each of the four tires needed to be replaced inside of a ten day period - each from seemingly unrelated events - leaks, nail/screw, etc.)

Any insight would be of great value.

THANK YOU.
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Thursday, August 5th, 2010 AT 4:59 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Is there anyone that may have put something in your fuel tank? Also, have you checked for vacuum leaks? Can you tell me the last codes you found? Have you tried running fuel injector cleaner in the gas? Finally, when you replaced the EGR, was there carbon build up in the intake or the vacuum hose?

Sorry for so many questions. Let me know.

Joe
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Thursday, August 5th, 2010 AT 10:50 PM
Tiny
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Hi Joe -

Thanks for your prompt reply to my query - -

I really don't know if someone might've put something in my fuel tank - but I suppose it is possible. I also suppose I'd have to remove the tank and actually look inside it to see if this is the case? I believe the mechanics helping me (who're both perplexed) checked vacuum pressure - but I don't know if that rules out leaks or not. I will check again and get you the most recent codes - the last codes I know were for the ignition system - which is why we replaced the module. I have not tried fuel injector cleaner in the gas, but I believe my mechanic checked and cleaned the injectors. I replaced the EGR myself and I did not notice any carbon build-up on either the intake or vacuum hose - apart from a very tiny bit of grime (which I scraped off with a razor blade before installing the new gasket and then the new part.)

Thank you for your questions! I hope this info helps clarify some issues - - I'll check the codes again and post the results ASAP.

- PR
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Monday, August 9th, 2010 AT 10:15 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Let me know the codes when you get them. It will help. Also, they should be able to get fuel from the schrader valve on the fuel rail. Maybe they can tell if something has been added.

Let me know.
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Tuesday, August 10th, 2010 AT 12:39 AM
Tiny
MRODONATA
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Hello again! I have had some other issues taking unfortunate precedent for a bit (clutch/t.O. Bearing and more for my other truck - a Chevy '70' dump truck - and minor repairs/maintenance on a New Holland skidsteer... AND, believe it, other trouble with, I think, the starter for this truck now too! Seems to draw down the voltage from 13V to less than 9V every time I start it - - just this week needed to jump it several times to get going. Test shows the battery to be good. Could this be at all related to my other issues?)

But back to my still persistent running problem(s)...

The codes I now get are "36" (Idle Speed Control Actuator - which sounds very likely to me) and "54" (Fuel Pump Relay - sounds likely as well... But not as sure how to proceed with checking this one myself though). I also get a "12" code, but I think this just indicates the diagnostic feature is working.

Thank you!

-PR
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Thursday, August 26th, 2010 AT 12:30 PM
Tiny
MRODONATA
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Also, I'm [over]due for a follow-up on my check-up by the transmission place - had that replaced around April-May... Running problems started the day I got the truck back - but had been sitting for mayvbe six weeks prior to replacing the 4L80E transmission.

Someone else suggested I ask about the 'modulator valve'...

Any thoughts on this?

I actually now need to solve my starting problem before I can proceed anywhere with confidence - - the battery seems good, and had a new alternator put in a little over a year ago... I'm expecting it needs a new starter - if/unless I can eliminate wiring/connections in the process.

If I can figure out the starting issue, I'll probably be in for the tranny check-up yet this week.

Thanx again!
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Thursday, August 26th, 2010 AT 12:39 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
It sounds like you have the same type of luck as I do. As far as the no start, it sounds like the starter is drawing too much power. Your battery should maintain a minimum of 9.6 volts for the ignition system to work properly during start-up. If you can get it to a parts store, they can check how many amps the starter is drawing. That way you can be sure it is the problem.

As far as the other truck, a code 12 indicates no distributor pulse. However, it can also indicate the start and end of the scan. As far as the other items, the idle air control valve will cause an eratic idle and the engine to die at a stop. The fuel pump relay is the cheapest thing to try because I am sure you could find another relay on the truck with the same part number and switch them to see if that helps. If it doesn't, I would say the IAC is the most likely suspect.

Let me know what you find on both vehicles.

Joe
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Thursday, August 26th, 2010 AT 9:23 PM
Tiny
MRODONATA
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Hello -

so sorry to confuse things with info about the other truck - - the starter issue is actually with the Silverado (not the dump truck)... Anyhow, it was at the store that we confirmed the battery was good, but an issue with the starter - just not sure if I only need to replace the solenoid or the whole starter. Working on this now.

Your description of the idle air control valve (idle speed control actuator?) ". Will cause an erratic idle and the engine to die at a stop" describes my symptoms perfectly. Yes, the Fuel Pump relay seems easiest and cheapest - could it be that this sends a signal/power to the IAC? Otherwise it seems like I may need them both.

I'll try the relay 1st - and then - if not solved - the IAC is my [final!] Hope!

I'll post my results.

- PR
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Friday, August 27th, 2010 AT 9:26 AM
Tiny
MRODONATA
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Okay -

... Long day... Replaced my junk starter - one success!

I also removed and 'tested' the IAC - - by checking the ohms on each pair of contact points in the plug receptor - I got a steady 45 (or was it 54?) On each pair (the Haynes manual says the range should be between 40 and 80 ohms). This seems to suggest that the part is working... But the problem persists! I also 'checked' the Fuel Pump Relay... I don't have a matching relay - - it seems that it should either work or not - - and I never get no gas - just the wrong mix and absolutely errant idling. Oddly, I get gas with as well as without the relay in place! Shouldn't it kill altogether without the relay - just like a blown fuse? I also noticed the 'feul sol' fuse was missing - I replaced it with a 30 amp fuse - but don't know what this might affect.

A friend may have a matching IAC for me to test against this apparently (but not certainly) working one of mine - if that affects the performance, then I'll know if it's the cause...

- PR
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Friday, August 27th, 2010 AT 5:48 PM
Tiny
JACOBANDNICKOLAS
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If you pulled the relay and are still getting fuel, someone had to rewire something. Like you said, removing the relay should kill the power to the pump. Has anything melted down where the relay attaches?
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Saturday, August 28th, 2010 AT 12:41 AM
Tiny
MRODONATA
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Nothing melted by the relay I can see... I did notice that the whole fuse box is under the hood - - in my [Haynes] manual it says that the fuse/relay box should be behind the fire wall in the cab on a '95 model truck - and where it actually is on models '96 and newer...? Why might this be? I believe I have a '95 Silverado.
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Monday, August 30th, 2010 AT 8:39 AM
Tiny
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It could be because when it was produced.
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Tuesday, August 31st, 2010 AT 11:25 AM

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