Misfire and rough idle at start up.

Went out on some trails yesterday, and had some rough running problems. When i first crank the jeep up it runs rough. Today it got worse. First, my oil pressure gauge was maxing out at 80 psi. It eventually stopped doing that. Then when i went to crank it up one time, it would barely stay running, and then the check engine light started flashing. I immediately shut the jeep off when that happened. I checked every thing over under the hood, and there wasnt mud on anything real bad. There was some on the alternator. After i let it sit for a few minutes i cranked it back up and was running a little bit better but still rough, and the CEL wasnt flashing anymore but was still lit.

I checked the codes and it said i had a cylinder 2 and 4 misfire. also on the way home the temp gauge would shoot up to the first redline and then go back down to about 215.

The rough running stops once you get going.
Any ideas on this issue.

Sorry, forgot to say my Jeep is a 2000 Sport 4x4.

Search heat soak. Its a common problem with that year XJ due to the pre-converters mounted under the intake. I had some luck with wrapping the fuel rail and injectors in the cheap header wrap but it will still do it if its over 95 out.

The oil pressure spiking is almost for sure the oil pressure sending unit starting to act up. Generally, they read HIGH when they fail. Get a new one at Jeep if you replace it......

I have thought about the sending unit, but since the problem with the temp gauge and oil gauge happened at almost the same time, i thought they might be related. Do you think they could be?
I will try wrapping the injectors with the wrap. Heat soak only happens when the motor is hot, right? Well I still have rough idle problems in the morning time too, when the motor is not warm or hot. The rough idle goes away once i start driving for a minute. What could be causing this problem?. There were no codes stored before i got the heat soak.

warmhambone said:

Well I still have rough idle problems in the morning time too, when the motor is not warm or hot. The rough idle goes away once i start driving for a minute. What could be causing this problem?

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If you have a rough idle upon a COLD start and it is fussy for a few seconds and then the idle straightens out, it is possible that you have a leaky fuel injector.

If an injector leaks raw fuel into the cylinder, the engine has to burn off that excess raw fuel upon startup and therefore runs kind of rough for a while.

A good fuel pressure gauge and a factory service manual detailing some fuel pressure "leakdown" testing would tell the story here. I think it might be worth a try if you consistently have an issue with cold starts.

If you are experiencing heat soak, it can present when the engine is cold as the boiling away of the fuel in number 3 injector that fuel is gone even after the engine cools off.

Try opening the hood after shutting off the engine and leaving it open until you restart or about 30 minutes if you are done driving for the day.

If the symptoms go away, or are less of a problem, then it is heat soak.

Thanks for all the replies everyone. I havent had a chance to check anything out yet. The Jeep hasnt even been started since this incident.
It may have been a misfire on cylinder 3 & 4 instead of 2 & 4 now that i think about it.

The rough idle on a cold start was caused from a bad coil pack. I put a different pack on and it idles fine now. I still have to address the heat soak problem though. Thanks for your replies