I picked up a 2000 k2500 with a 454 a few months ago and I’ve been trying to fix a misfire since then and I’m out of ideas. It seems the misfire is most noticeable when under load under 3k RPM, or at idle. Cylinder 3 and 5 are the ones misfiring. I have replaced the MAF sensor, IAC valve, EGR valve, O2 sensors, spark plugs, spark plug wires, distributor, the whole fuel system, and even the injectors, but I have made no progress. Has anyone else had an issue like this, or any ideas where to go from here?
Very persistent misfire, help
- Thread starter BillyGoat
- Start date
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I have been running into the same thing in my 90 K3500
udidwht
I'm Awesome
Spider injector
Did you use Delco parts?
Did you use Delco parts?
I don’t know spider did but in my case I have . His and my case sound near identical
454 doesn't use a spider injector.
How do you know it's 3 and 5?
Cranking compression test?
Inspect the spark plugs while they're out. What did the old ones look like?
Inspect the plug wires, and plug wire routing.
Pop the valve cover, look for bent pushrods, broken valve springs, stuck valves, rocker arm problems. Do the valves all move about the same amount when you crank the engine?
How do you know it's 3 and 5?
Cranking compression test?
Inspect the spark plugs while they're out. What did the old ones look like?
Inspect the plug wires, and plug wire routing.
Pop the valve cover, look for bent pushrods, broken valve springs, stuck valves, rocker arm problems. Do the valves all move about the same amount when you crank the engine?
I know it’s 3 and 5 because the manifold temps out of those are significantly lower than the other 6, I also got a lean bank 1 code just this morning after not throwing any codes since I’ve had it. All of the valvetrain is okay but I haven’t done a compression test yet.
When my '97 had a misfire indicated on Cylinder 8, it turned out to be a cracked spark plug porcelain.
Replaced the plug, misfire gone.
Replaced the plug, misfire gone.
ambisinister
Newbie
I have a similar issue with my 98 5.7. #6 codes a misfire, only noticeable at idle. Replaced distributor, coil, plugs, wires, module, and upgraded the injectors. Cranking compression test showed 140 to 165 psi on all cylinders. And #6 isn't the lowest one.
MAP sensor. The map sensor is used to determine load and the computer adjusts timing and fuel accordingly. If your sensor isn't reading correctly you will have random misfires under a load. I chased this problem for almost 2 weeks on my 98 tahoe 350 vortec. It would only misfire up a hill under medium load, not hard acceleration and almost always throw P0300 (random misfires) and P0305 (misfires #5).
Steve A
I'm Awesome
Have you checked the injectors for those cylinders? Any possibility the injector wiring for those two are crossed? An injector noid test light would tell you if the injector signal from the ECU is getting to the connector.
