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Rough running

Tiny
MIKESDOG
  • MEMBER
  • 1987 CHEVROLET TRUCK
  • 175,000 MILES
My chevy 1987 chevy Scottsdale with a 350 tbi sometime runs smooth then sometimes runs like its running with half the power or less like it has bad gas or something. I have replaced the fuel filter, oxygen sensor, air filter, it doesn't matter which tank I run it on, I've used fuel dryer (Heat) changed pvc valve, could be a injector going bad? They seem to be spraying fine when I look at them but that has been when the engine is running fine. Doesn't matter if the truck is warmed up or not it can run fine for some time then out of the blue run so bad I have to keep it floored to keep it running also replaced cap and rotor.
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Wednesday, September 4th, 2013 AT 1:22 PM

14 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,883 POSTS
These trucks had a problem with the ignition coils I would also check for the ground strap in the distributor.

If the EGR valve is stuck open due to a carbon chip you will notice rough running at idle and low speeds when it is supposed to be closed, but it normally opens at higher speeds. You shouldn't feel it there. Throttle position sensor won't cause this either. At worst it will cause a hesitation or stumble on acceleration. It has the least say in how much fuel goes into the engine. The Engine Computer is a possibility if it fails to drive one of the injectors. GM did have a lot of computer trouble from the mid '80s through the late '90s.

If you can keep it acting up, most mechanics have scanners that have a test mode that allows you to fire each injector repeatedly. If it says the test is running but the injector isn't clicking or spraying fuel you can do some electrical tests to determine if there's no voltage getting to that injector or if the computer is not grounding the control wire to it.
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Wednesday, September 4th, 2013 AT 2:17 PM
Tiny
MIKESDOG
  • MEMBER
  • 2 POSTS
Good call on the ignition coil I got a new one and installed it runs great! I Love this site.
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Friday, September 6th, 2013 AT 2:17 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,883 POSTS
Good to hear, please use 2CarPros anytime we are here to help.
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Friday, September 6th, 2013 AT 8:25 PM
Tiny
WRANGLERMAN
  • MEMBER
  • 2 POSTS
  • 1987 CHEVROLET TRUCK
  • V8
  • 2WD
  • AUTOMATIC
  • 50,000 MILES
Hello I have a 87 chevy pick up when I start it if its cold it runs rough also back fires threw the throttle body( truck has a 5.7 tbi with 50000 km on rebuild) if its milder out it runs good! Could there be a sensor going?
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Check for any codes in the ECU and do a general tune up, most problems like this are tune related.

Mark (mhpautos)
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
WRANGLERMAN
  • MEMBER
  • 2 POSTS
Thnks for the reply ive recently did a full tune up and oil change also added a k&n air filter. Had the codes checked and it came back a code 12 was told probly because the factory air is disconnected why the code is there?
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
JTCOM
  • MEMBER
  • 1 POST
  • 1987 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 120,000 MILES
Running rough under load like plowing, it idles ok but it start to cough, and buck under load. I used some dry gas, fule injection cleaner, sometimes it smooths out, but runs rough again. Fule filter will be next thing I will replace.
Any idea of what may cause the running rough?

Thanks,
jtcom
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Three come to mine
tune up and wires (check spark plug wires )
fuel filter and fuel pressure
restricted exhaust
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
METALIC1666
  • MEMBER
  • 1 POST
  • 1989 CHEVROLET TRUCK
  • V8
  • 2WD
  • MANUAL
  • 104,000 MILES
I started my truck this morning and it fired right up but was running bad poping while I burp the throttle, I drove it to work and it didnt get any better. Shut the truck off and went to restart it and nothing not even a click, battery has plenty of power all lights horn work. Poped it again and was still running badly. Any help would be great
thank you.
Nate
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Popping thru the carb area? Can be a worn camshaft lobe or two, When was the last complete tune up? And timing may be off for whatever reason. Ignition module or pickup, inside your distributor.
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
ROGERBIRD
  • MEMBER
  • 4 POSTS
  • 1985 CHEVROLET TRUCK
I have recently broken a crankshaft and replaced it bearings and 2 damaged pistions and all piston rings.
After reinstallation of the engine, it would run poor.
After driving for10min, it will start skipping and try to stall.
Typically it will not log a code, unless it sucessfully stalls, then I get a 42 code. I have externally tested the Ign. Control module (EST), it tested fine, but since it seemed to be a heat issue, I have replaced it.
If I accelerate it will continue to run. The engine runs fine on cooler mornings or rainy days. I have cleaned the carbon out of the EGR valve.
Prior to the major engine work it was running good.
10 months ago I had replaced the Fuel Pump, Fuel Filter and both Fuel Injectors as well as the ECM - For a different issue.

Where do I go next?
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
ROGERBIRD
  • MEMBER
  • 4 POSTS
I replaced the IGN control module (EST) and distributor cap, Still runs bad.
Finally took it to a Diag place. And every thing checked out fine, and their 'expert' opinion it has a bad fuel pump.

I had replaced the pump and filter last september, due to a full failure of the pump. Guess I go t a bad one, gonna try replacing it this weekend.

Let you know.
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Tuesday, July 30th, 2019 AT 11:09 AM (Merged)
Tiny
ROGERBIRD
  • MEMBER
  • 4 POSTS
Well, I installed the new pump screen and filter.
Still runs poorly, Now it doesnt even take 10min.

Initial starting sometimes will surge at idle, 2000rpm down to 500rpm. If I restart or rev at 2000 for 20sec. It will run. I am getting intermittent Check engine lights (Code42) when it is running ok (ocassional misses) after a while it will begin to try to stall (and often does stall) and I will not get a code or a check engine light if that happens.

The Diag place, wants another $90 to 'begin again' since I replaced the pump and filter myself (instead of paying them $385).

It seems like I am fixing little cascading problems and never getting to the end.

Anyone have any I deas?

This is an '85 Chevy Elcamino V6 4.3L - Fuel Injected.
Have just replaced a broken Crankshaft+ bearings/#1+ 2 Pistions/ and all rings. - Less than 200 mi since replacement.
I have cleaned out the EGR valve, replaced the EST (ignition)Module and Distributor cap.

Roger
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Tuesday, July 30th, 2019 AT 11:10 AM (Merged)
Tiny
ROGERBIRD
  • MEMBER
  • 4 POSTS
OK, I replaced the Fuel pressure regulator, now the car starts right away, still runs fine on cooler or damp days, and idles fine, but while driving randomly stalls, while still rolling, if I floor it, it will resume running (Dont have to turn the key) It will continue to run, typically it does not log a code. If it runs without stalling, I do get a check engine light that will blink on and off, and sometimes will stay on. (Guessing code 42 still). I am running out of things to change out. Does anyone have any ideas? What I should check?
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Tuesday, July 30th, 2019 AT 11:10 AM (Merged)

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