1987 Chevrolet Truck rough running 350 tbi

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

3 Replies

Tiny
CARADIODOC
  • EXPERT
You might try wiggling or tapping on the injector connectors to see if one injector cuts out intermittently. If it does, unplug it and pick the terminals so they make tighter contact.
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Wednesday, September 4th, 2013 AT 2:17 PM
Tiny
MIKESDOG
  • MEMBER
I tried wiggling all the wires to the injectors did change the way they worked still pulsing good and wiggled all the wires from the coil didn't change any thing. Could the egr be affecting anything?Or the TPS, OR ECM?
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Friday, September 6th, 2013 AT 2:17 PM
Tiny
CARADIODOC
  • EXPERT
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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Friday, September 6th, 2013 AT 8:25 PM

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