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Random Misfiring Issues....

ewert35

NAXJA Forum User
Location
denver co
I was wondering if someone would be able to provide some direction for my engine issue. I just added a new lift and did some axle work, but I doubt that had anything to do with the new engine problems.

This issue occurs very randomly and maybe once a month, or if I'm running a lot of errands in which I'm turning the Jeep on and off several times within a short period of time.

The problem begins when I start up the Jeep, from a cold start or a warm start, happens in both circumstances, the engine idles extremely roughly. With a little added gas to rev the engine up, everything returns to normal and the engine idles as it should. About a minute or so after the idle goes away, I get the ODB codes for random cylinder misfire... typically cylinders 1,2,3... never the rear 3.

Once I have rev'ed the engine and it returns to normal, it doesn't happen again during that trip. If I shut off the Jeep and turn it back on shortly after, I can expect it to happen again unless the Jeep has been off for the whole night.

So far, I have complete an oil change, new plugs, new coil, and cleaned the throttle body.

Im pretty handy and have the ability to fix the issues on my owe usually, I just need so direction and advice on where to start?

(Jeep XJ 2001, 4.0)

Thanks so much for the help! Truely much appreciated!!!
 
Welcome the late model hot soak misfire problem.
Do a search and you will find dozens of threads.
There is no dependable cure, I know, because I have tried every one over many years.
The problem is worse in hot weather when the engine is hot and then shut off for 5-20 minutes. The dual mini-cats, found on some 2000/2001 XJs, dump to much heat into the engine bay
and causes the fuel, in the fuel rail, to evaporate, leading to the what is best compared to vapor lock.

My solution is a timer that runs the electric auxiliary fan for 2-3 minutes after shutdown.
http://www.flickr.com/photos/lwade/sets/72157617434915718/
 
Im in the same boat as you are, and by whatever fluke chance, i started throwing P0303 code just after i installed my new lift LOL. 2001 XJ.

same symptoms, same heatsoak problem as everyone else. i am going to copy your idea there and wire in a fan timer, and use some of my mini mercedies squirrel fans.. better than cutting holes in my hood.

Thanks!
 
Shouldn't be too much of a problem for you right now since it is winter, assuming you live in Princeton, NJ. I get the pleasure of experiencing it year-round in our warmer climate.
I had an occurrence last week that took several minutes to clear and set off several codes. I carry a scanner all the time for clearing codes in case I forget to set the timer. More XJ joy.
 
^^^Exactly.

Rough running from a cold start is not heat soak. Trust Talyn on this one. That being said, installing an after run timer to operate the Aux Fan is a good idea.

My setup runs the water pump (yes, it is electric) for 2 minutes after shut down and drops the engine temps by a good 10F on a summer day. Zero heat soak issues.
 
I have '99 4.0 and I am experiencing the exact same issues with the cold start. Would the TSB for the PCM cold start issue also apply to a '99? Could someone direct us to the TSB for the PCM cold start? Thank you very much.
 
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