4.3 misifre

Asked by Jul 22, 2017 at 06:13 PM

Question type: Maintenance & Repair

I have a 93 Chevy C1500 WT. It idles fine but
misfires when under a load. I've replaced plugs and
wires, TPS, TCS, MAP, ECM, ECU ( computer went
out ) and fuel pump and as soon as I take off and
hit 20 mph it starts misfiring like crazy. Any ideas
on what this could be ?

3 Answers


Got to start with basics. Plugs, Wires and those things eat distributors and rotors. Gas filter clogged? All the fuel injectors working and properly? Any wiring issues on injectors? Carbon buildup on throttle body and IAC? How much fuel pressure is there? Broken or cracked vacuum hoses? Plenum or intake gasket leak? The old carburetor cleaner trick while revving engine might find a vacuum leak or gasket leak.

I discovered that the fuel pump needed to be replaced a few weeks ago and I thought that was what was causing the backfire. Replaced it and nothing changed. Done the carb cleaner trick, absolutely no vacuum leaks. Only thing I can think it may be is the throttle body as you just said.

Everything from sensors, plugs and wires and fuel filter has all been replaced with new parts.

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