I have a 1994 gmc Sierra 1500 5.7L. It is running like crap. It is rough at idle and stall when you put it in gear. I've rebuild the throttle body and it still won't stay running.

Asked by Nov 10, 2015 at 09:39 PM about the 1994 GMC Sierra 1500 C1500 SL Standard Cab LB

Question type: Maintenance & Repair

My boyfriend thinks its the o2 sensor I
honestly thinks its the spark plugs
and cap and rotor and the wires. Need
help

3 Answers

115,605

If it has not had a recent tuneup then that is the place to start.

3 people found this helpful.

All to often people jump to 02 sensors as a problem when more often they are not the culprit. o2 sensors will never cause a no-start, and if bad the worse case is an off fuel/air trim. I agree with FoR, that's the place to start since it is not OBDII to get a code. And make sure the catalytic converter is not plugged

3 people found this helpful.
240

94 GMC sierra with a 5.7L.... Bad ground, probably, or dead short, maybe, somewhere in either the wiring harness or instrument panel..... It's a bitch to find it, and tossing parts at it will sometimes "accidently" fix the problem for you. But only if you changed the sensor or other part that just happened to be the one with poor ground connection..... Could also be a dead short in something causing power to drain through the short, but only when a signal is received by the ECM from one of the sensors that winds up grounding out the signal that normally controls the Idle Air Control valve, or the fuel injection circuits..... I ain't a mechanic, but I've been trying to chase down that same problem now for almost three weeks..... Problem started with the 305 that was in the truck, came right back up after dropping a newly rebuilt 350 in place, along with virtually all new sensors and valves from the start.... There is either a dead short, or a piss poor ground on "something" or in some part of the wiring harness causing the problem in thousands of GMC trucks. If all the questions regarding the same identical problem is any indication. It's going to be an easy, and cheap, fix if you can find it. The headache comes in trying to find it.

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