4.0l engine check engine light

[chris142]

The 4.0 valve rotators won't rotate the valves below 3500 rpm.So if you never rev it then carbon builds up on the valves which causes weird things.

W/O a scope or diagnostic stuff were only guessing. The coil is a good place to start and check fuel pressure.

[cjkarl]

Engine missfires

Yup replaced coil( x 2 times ). Check fuel pressure and flow, both are as specified. Compression and leak-down no problems. Found out that valve springs may be weak and causing problems. Checked valves and all are rotating as to wear patterns on end of stems. Did the whole Sea-foam deal to decarbonize in tank, crankcase, and down intake, etc. New springs #61 lbs @ 1.650". Have to pull old springs to get lbs on them. Cannot think off anything else to remedy this short of changing computer not to recognize random miss-fires and turning on CEL

[cjkarl]

engine missfires

Use a Snap-on MT2500 for diagnosis. Shows a Random missfire at light loads and never the same cly/clys. Different speeds and different roads ( not a rough road/loose connection )

[inVERt'D]

Since running the Sea-Foam seemed to help, perhaps a professional cleaning will help more?

[Jeeperator]

I had the same issue and My jeep wasnt going to pass smog because of the cel. I also saw the tsb about carbon build up and I used an old trick I learned in auto shop back in high school. While running the engine above 3000 rpm I poured (small) amounts of water in the throttle body. It basically steam cleans the inside of the engine and knock the carbon off the pistons and valves. Went to smog the next morning and it passed cleaner than my Honda and hasn't thrown a cel yet.

[OU812]

Ive seen our techs at the dealer do this.

[inVERt'D]

I've heard of that trick too, but I never think to do it...hmmm...

My Dad was making these Brown's gas boosters for awhile and running them in his cars. He said they really cleaned out his engine, and I believe it. I might run one in my Jeep for awhile just for that reason.

[6spdYJ]

How much water are we talking about? A stream from a squirt bottle or a mist?

[OU812]

Imagine taking half of a bottle of water and pouring a small stream into the throttle body will you are holding the throttle open with the engine at about 2k RPM. The half of a bottle of water would take about ten to fifteen seconds to pour.

[cjkarl]

engine missfires

Done Fixed it

[chris142]

What was it? Carbon?

[bails85]

the water is an old school trick that most hot rod guys used to use. especially on 350s. works well. i used to just pour enough to make it want to stall then repeat a few times. water is an excellent solvent that most forget.

[2blk2drs]

Yet another reason snorkels are pointless.....

[Jeeperator]

Did my internal engine steam cleaning recomendation work?? Just remember too much water will destroy your engine because water don't compress and rods will bend and pistons can break. Hydralicing your engine is not good.

[Lumpy Grits]

Use a spray bottle with distilled water.
This has worked well for me for over 45 yrs.
Cheers,
LG