So a while ago I was driving my truck the check engine light came on. It was a #5 misfire code with no other codes stored. I cleared it just for kicks to see if it would come back, and for a while it Didn't. Then a couple weeks after that it came on twice and went away for a couple days same code and all. The day after that it came back on with the same code, but this time I was noticing that it had a rough idle this time. So the first thing I did knowing it most likely had a tune up in some time, I replace the ignition coil, cap and rotor spark plug wires, plugs, and started it again. After I did all that it was acting the same. So I decided to check compression all of them passed with good compression. So I moved injectors 5 and 6 to see if the misfire would move with it, It didn't. After I got finished with that I ripped the intake off and replace the plenum and manifold gaskets. Started it up seemed to run fine for a while but it went right back to the same old right idle. I assume it just seemed to be running fine because it runs fine at higher rpms. So after I did all that for kicked because I've worked on these engines a lot I divided to do head gaskets. I'm in the middle of that right now. I just don't know what else to look for now. I've never ran into a problem like this. So if anyone has some info I would greatly appreciate it.

 

If memory serves, the PCV valve is on that side in 2001. Hit the dealership for a new one.

 

I have replace that too. I forgot to put that.

 

Oh, okay then. Other things I'd look at, assuming that the compression test has ruled out mechanical problems in the combustion chamber and valve train:

• TSB 18-48-98
• Got plain jane copper plugs installed? (If not, try a new one in #5.)
• Got an exhaust leak? (Will fool sensor.)
• Swap plug wires 3 and 5 at both ends -- does problem move to 3?
• Swap plugs 5 and 7 -- does problem move to 7?
• Get it on an ignition scope.
• Check injector pulses with oscilloscope.

One of those things should point out the failure.

 

I didn't have any exhaust manifold gaskets on there as far as I could tell. And I do have a couple exhaust leaks. Wouldn't that make it run rich?

 

It would run rich, but the PCM wouldn't know of it, and the catalytic converter would mask the smell except for that brief period between the PCM going closed loop and the cat reaching operating temperature.

 

I'll have to take it in and have it patched when I get it all put back together again. Because I have a leak around the cat and my muffler has come lose. I'll try all the things suggested.

 

The muffler won't cause misfire indications. Leaks around the upstream side of the cat will usually cause random cylinder misfire indications rather than just a single cylinder. Leaks upstream of the cat, though, will often tend to favor one or two cylinders.

Good luck with it!

 

So leaks upstream of the cat will cause random cylinder misfire indications not specific to one cylinder but also cause misfire indications that favor one or two cylinders? Im a tad confused lol

 

Leaks at the cat, on the upstream side (closer to the inlet(s) than the outlet), will cause random misfire indications. Leaks completely upstream of the cat (actually the pre-cat oxygen sensor), at the manifold, for example, will cause more consistent misfire indications.