After inspecting the cam for warn lobes, I just assumed it must be rockers. I mean I replaced everything coils, wires, plugs, injectors, O2 sensors. My HG job sat idle for a while with the heads off, and I was concerned a rocker may have been sticking. I ended up soaking the assemblies in a degreaser bath for a while, the towers were pretty gunked up. After oiling and re-installing my misfire went away and hasn't returned. I know it's probably last on the list of things to do, but that was my experience.

 

So an update is in order...
I changed the #1 (the offending cylinder) spark plug and wire again and the o2 sensors.
After resetting the codes it started and idled perfectly...... Then after about 5 minutes I reved it up and the light started flashing again and the same codes misfire #1 and catylitic failure blah blah..... and it went back to a rough idle.
Reset codes fine at idle - Rev motor to 2500rpm and the code flashes and then runs rough....
So now I have new headgskets, plugs, wires, coil packs and o2 sensors and a truck that runs like crap - time for matches or a new motor,,,?

 

Did you replace the fuel injectors?

 

I think it's very interesting that clearing the codes resolves the issue.


After you clear the codes, will it idle smooth indefinitely? In other words, can you attribute the issue to RPM or to run time? I'm not sure how long you let it sit after clearing code, but I wonder if that could be related to engine temp?



If it is RPM related then I would investigate things that change with RPM. MAF, fuel pump, vacuum leak? Your spark/electrical sounds solid. I know it is a PITA, but it may be worth pulling the lower manifold and looking at the cam shaft lobes?

 

I had an issue like that which turned out to be a cam lobe. It would idle perfectly until there was a load on it. You could even drive like an old lady around town and not really notice. At that time I did not have the ability to clear the codes though, which is an interesting aspect... I never had a rough idle after the CEL came on and flashed, it misfired under load, idled smooth again with no clearing codes.

 

 

 

I clear the codes and immediately start the truck and it runs smoothly.
It seems to be under load that it misfires and then idles rough.
Seems to me that if it was a cam lobe it would cause a misfire all the time.... When we did the headgasket we replaced the lifters and there was no visible wear on the lifters/cam..... I may have to try an injector.....

Thanks for all the input gents - will update as this progresses.
:c heers:

 

If you remove your #1 spark plug and disconnect or remove #2-7 wires/plugs you can turn the motor with the start to see if oil or coolant is pouring into #1?

 

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Check the harness for the injector, especially right at the injector, notorious for breaking/loosing contact in this area. If harness looks good, pull injectors and have them rebuilt or replace.

Brian.