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Mudderoy
03-30-2010, 08:57 AM
In the morning the 4.0L runs a little ruff. Nothing that you'd probably notice unless you knew the vehicle, or the 4.0. After about 5 minutes it's fine. The running ruff doesn't seem to effect acceleration.

I've been having a "CHECK ENGINE" light come off and on since July last year. It goes month(s) at a time and then I'll get a series of them for say a month. It's always misfire cylinder #5.

I've been thinking cracked head, bad head gasket, or leaky injector(s).

I don't think it is a cracked head, or bad head gasket. The O2 sensor reports a rich fuel environment, so again I'm thinking leaky injector.

Any ideas, or experience that would confirm or deny this theory?

rguignard
03-30-2010, 09:47 AM
i know something to try that is free. try changing the fuel injectors around put the #5 in the # 1 hole and see if the miss moves with it that would tell you if its the injector is the problem :thumbsup:

4.3LXJ
03-30-2010, 10:10 AM
You could have dirty injectors too. A can of Sea Foam in the gas tank will fix that. Don't pour it down the intake. Just in the gas and drive it.

Mudderoy
03-30-2010, 10:57 AM
You could have dirty injectors too. A can of Sea Foam in the gas tank will fix that. Don't pour it down the intake. Just in the gas and drive it.

Never seen it, I'll have to ask at the parts store. Thanks.

BlueXJ
03-30-2010, 11:59 AM
The misfire code does it happen only after the engine is at operating temp? There is a TSB about a heat soak problem with the injectors at operating temp and the dealer must fix it for free. It involves some sheilding on wiring and insulation on the offending injector.

Asa to the running rough I would have to hear it to help with that diagnosis, sorry Muddy.

Mudderoy
03-30-2010, 12:26 PM
The misfire code does it happen only after the engine is at operating temp? There is a TSB about a heat soak problem with the injectors at operating temp and the dealer must fix it for free. It involves some sheilding on wiring and insulation on the offending injector.

Asa to the running rough I would have to hear it to help with that diagnosis, sorry Muddy.

I thought the heat soak was on the 1999, or later 4.0 XJ, plus it didn't happen for the first 11 years of it's life. :rotfl2:

firehawk
03-30-2010, 08:41 PM
The misfire code does it happen only after the engine is at operating temp? There is a TSB about a heat soak problem with the injectors at operating temp and the dealer must fix it for free. It involves some sheilding on wiring and insulation on the offending injector.

Asa to the running rough I would have to hear it to help with that diagnosis, sorry Muddy.

The TSB I saw (and had problems with) was about heatsoak in the #3 injector. They wouldn't fix it for free, I had to buy the "kit" and fix it myself. The kit consisted of a piece of insulation "tubing" you zip tied around the injector.

It appears the #3 injector is over an opening between the intake and the exhaust manifold. The heat from the exhaust was rising up and evaporating the fuel out of the injector. It will run VERY rough until the fuel pump can refill that injector. Ethanol in gas will evaporate faster than gasoline, so the ethanol content in gas now makes the problem worse. With out the alcohol content the octane rating goes WAY down... again making the problem even worse.

FYI, the kit that was supposed to fix the problem didn't. I've found that if the Jeep is hot, I turn the key on and wait about 10 seconds before cranking. That appears to allow the injector to fill back up (so to speak) and I don't have the problem.

4.3LXJ
03-30-2010, 09:37 PM
Hey Muddy, they starting to put alcohol in your gas now down there?

Mudderoy
03-30-2010, 11:10 PM
Hey Muddy, they starting to put alcohol in your gas now down there?

Yep!

4.3LXJ
03-30-2010, 11:13 PM
There might be something to the heat soak issue then. Mud Deprived just did a fix for that. Says it works so far.

BlueXJ
03-31-2010, 01:00 AM
I think the TSB was originally issued for 99s but was later expanded to include some 98s from a certain vin on.
It may have been for the #3 injector but the #5 is just as prone to have heat related problems due to exhaust problems.