2004 1500 5.7l recurring problem, low idle misfires, no MF under load.

[Bills86e]

rpm at idle goes 200. MPG OH counter 7.8 MPG. I had had similar problem so replaced engine. Now have 16k and still cannot figure same code p0300 misfire cylinder 7.
,,
New injectors, spark resister plugs, wires, & coils. All sensors new, checked all last week. last week, & new oil/filter. Pulled driver side valve cover and all in spec.

Can PCM be culprit?

 

[jws123]

Did you check compression on all cylinders? Its almost never a PCM issue also did you check for vacuum leaks?

 

[Bills86e]

soon as the rain stops. Going to throw another CPS, gets here Friday. How do I check intake manifold? While running I did spray (lightly) but no change in engine rpm.

 

[Bills86e]

OK, I have the fix, I,ll explain. The new CPS resulted in No Change. P0300 is the result of mil light. Low oil pressure makes hemi tick more prominent.
Since the rpm is controlled by the PCM, it is BAD, and I have ordered a Plug & Play PCM from FlagshipOne $228 shipped.
When RPM goes low, there is no way to get it back to 750 RPM.
When the 5.7l goes lower than 650, oil pressures are low to almost non-existant, ticking begins.

This should also return my MPG to normal. I,ll report back.

Queation: Are 4wd shocks compatable with R2wd trucks?

 

[Bills86e]

Will not idle 750, at 200, lifters clattering, op goes to zero oil pressure.
good compression, new HV melling op, freshed oil & filter, air filter, new pcm,
new exhaust manifolds & cats pipes, new battery, throttle body, op sensor,
coils, injectors. This is whacking my brain, I need advice.

 

[Ken226]

Have you checked the cam/lifters/valve springs.

For us 4th Gen guys, the p03xx cylinder misfire codes usually result in a cam swap or valve spring replacement. Especially on engines that have spent a lot of time idling.

It may not be a cam/valve spring issue at all, but since your scratching your head and out of ideas, it's something else you can check.

I think there was just a thread about this a few days ago in the 4th Gen forum. Similar code, broken valve spring.

 

[Dodge 1500 4X4]

I think there was just a thread about this a few days ago in the 4th Gen forum. Similar code, broken valve spring.

Yes he had a misfire, pulled valve cover and broken valve spring.