Good long rev of at 4K+ clears idle??

I keep thinking I have a burnt valve, because after a few days of driving, my engine will reliably misfire on cylinder number three. However, after revving the engine at 4000 or more rpm for 30 seconds in neutral or park, it idles perfectly. Any ideas?. 1998. 4.0 L recent rebuild, no codes.

In a day or two, it will come back. Is there a chance that the valve rotates just enough to leak, then rotates back? Or does it continually rotate. Or am I way off? I did a water test before I put the head on and also lapped all the valves to make sure they were good. When I try to start it, I know there is one cylinder with a slightly less compression or something because you can hear it as it starts it sounds a little different. Like ruh-ruh-ruh-ruuuuuuuh-ruh-ruh-ruh-ruuuuuh .After the revving, it does not.

I also wanted to add, it did throw a code. During the revving, I believe it's a P041 but I haven't checked it yet. It's done it before. I did notice that my miles per gallon indicator went from 13 up to about 17. Also doesn't smell like gas after the revving. After a while though all the symptoms come back, until I rev the heck out of it again.

Bad lifter maybe? Bleeds down and pumps up with the rpm? Check codes again, you're missing a digit. Have you checked compression when the problem is happening?

My bet is on a clogged injector. Run a can of BG44K. It will clean the injector and get rid of a ton of carbon.

I pulled the codes this morning. It was P0203, P0202, P0201, P0204, P0205, P0206, P0420.

Sounds like a ground wire maybe, as well as a new o2 sensor?

FYI, it's gone from running perfectly to misfiring randomly again about once every second or two. Nothing repetitive. I am going to run cleaner in it. Gotta get to the auto store. Hopefully they sell BG 44K.

And now it's misfiring constantly again. Sigh. See the time stamps

im betting the o2 sensor code is from the misfiring. and seeing it throwing a injector fault on all the injectors and not a misfire code. its almost certainly a wiring issue. check for corroded connections and fuses. not sure on this set up but typically the injectors have a constant 12v supply and the pcm switches the ground signal.

P0420 is a converter efficiency code. Need to fix misfiresbefore that, which could be a bad sensor or converter if it returns later. But you need to check wiring. Get a wiring diagram, it's probably a bad wire that all the injectors are branched off of (most likely power).

CarComp said:

I pulled the codes this morning. It was P0203, P0202, P0201, P0204, P0205, P0206, P0420.

Sounds like a ground wire maybe, as well as a new o2 sensor?

FYI, it's gone from running perfectly to misfiring randomly again about once every second or two. Nothing repetitive. I am going to run cleaner in it. Gotta get to the auto store. Hopefully they sell BG 44K.

Click to expand...

Those codes are for injector wiring circuit malfuctions, damaged wiring? Look for burned or damaged harness wires near the front drive shaft and exhaust manifold, especially the O2 sensor wires, if they melted they may have damaged Injector control wires....ECU...

CarComp said:

I pulled the codes this morning. It was P0203, P0202, P0201, P0204, P0205, P0206, P0420.

Sounds like a ground wire maybe, as well as a new o2 sensor?

FYI, it's gone from running perfectly to misfiring randomly again about once every second or two. Nothing repetitive. I am going to run cleaner in it. Gotta get to the auto store. Hopefully they sell BG 44K.

Click to expand...

With all six injectors throwing codes it may be a low voltage from the ASD relay. It's hard to imagine all six PCM drivers being bad. Swap the ASD relay with the radiator electric fan relay and see if it helps. With the ASD removed, examine the pin cavities in the PDC for corrosion.