Engine Misfire and Persistent Codes After Extensive Repairs - Did I Miss Something? (2004 Hemi, 82k Miles)

[dejvi d]

Hey everyone, I know we have plenty of experienced folks here, so I wanted to share my story and get your thoughts. I’ve got a 2004 Hemi with 82k on the clock. Since I bought it, the engine has been throwing intermittent codes—P0141, P0142, and P0300—sometimes all of them, sometimes just one, with a misfire and hesitation up to 2.5k RPM. Above that, it runs fine.


I eventually discovered a bad lifter, so I took the engine apart and replaced the lifters, cam, and push rods. I also had both heads skimmed and checked by a machine shop. Valves and valve springs were in good shape. After putting it all back together, the knocking was gone, but I’m still dealing with the same codes and misfire up to 2.5k RPM.


I’ve since replaced all 16 spark plugs with Champion copper/nickel, installed new NGK plug leads, and swapped out the ignition coils with Delphi ones—all to no effect.


At this point, I’m thinking the next step might be to replace the PCM, but I’m wondering if I’ve missed something along the way. Any advice or ideas would be greatly appreciated!

 

[jws123]

Wish you would of posted here before you did the cam as older hemis do not have camshaft issues also not likely the PCM. I would take it to a good shop have them look at the live data they should be able to find the issue also make sure your push rods are all seated.

 

[Ken226]

Yea, p0300 is random multiple misfires. Cam/lifter failure usually manifest on specific cylinders.

If you definitely had a bad cam/lifter, then perhaps these other codes are unrelated. Or, maybe something got left unplugged after the cam work.

P0141 and p0142 are o2 sensor heaters. Id remove and inspect the oxygen sensors. Start with those, since bad oxygen sensors could cause fuel issues that result in poor combustion and setting other codes. Like the p0300.