1994 GMC sierra still running rough

Asked by brandijeff Oct 09, 2018 at 09:29 AM about the 1994 GMC Sierra 1500 C1500 SLE Extended Cab SB

Question type: Maintenance & Repair

Replaced a faulty fuel pump about a month ago, still runs horribly bad.
I have been throwing parts at it ever since.
I have replaced:
Fuel Pump
Fuel filter
02 sensor
water temp sensor
cap
rotor
plugs
Ignition control module
MAP sensor
EGR valve
Idle air valve
complete rebuild of the throttle body and regulator
EGR solenoid
most of the vacuum lines

Still idles rough and stalls out at every stop.
no codes showing...??

Im sick of throwing these expensive parts at it, at this point I probably could
have just taken it to a shop and got it diagnosed.

anyone have any thoughts??

4 Answers
9,730

Mike answered 6 years ago

Did you replace the wires? If you did the next step is a compression test to check the engine condition, have you checked the ignition timng? If it's late by more than Four degrees the engine will stumble and stall.

Mark helpful

brandijeff answered 6 years ago

I did not replace the wires, they are only a couple years old. Timing is set. Drives and runs perfectly at highway speed, so it is really puzzling to me.

Mark helpful
9,730

Mike answered 6 years ago

You could have a large vacuum leak, can you ger to a scanner the reads live data stream? If so check MAP pressure with key on engine off it should be close to the current barometric pressure Then start the engine the pressure should drop if not you have a large vacuum leak or the engine isn't pulling a big enough vacuum in which case you're back to the compression or cylinder leak down test.

Mark helpful

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