Misfire

[joe_peters]

Is the "Heat Soak issue" something that happens after a certain number of miles or years on the XJs?

I ask because I'm having a heat soak misfire on my 2000 XJ with 152K. It was fine until this last spring. I have replaced the plugs, coil rail, and I feel like I'm chasing gremlins!!:gonnablow
I keep getting misfire codes, and had not thought to check the injector side of the system....because it was acting like an ignition issue.

I can run it back & forth to work (30 miles almost all highway) and it runs great, but once the airflow drops for a short time (like in normal city driving) it will start to misfire until it is shut off, and cools down again. The temp never goes over 210, but it still starts to miss. It is driving me crazy! :wow:

Tall Shadow :flipoff:

Quick and dirty test: drive it until it is good and hot, park it and open the hood fully.

Wait 20-30 minutes, then start it and see if the misfire is gone or appreciably better.

If it is, don't screw around with heat wrapping an injector--lame A** factory excuse for a fix.

Buy a timer and wire it in so that the efan runs for 3-5 minutes after shutdown. Link to timer here:

http://www.at-fairfax.com/P1786-ELK-960.htm

Numerous makes and models of vehicles come from the factory with this feature built in. It was most likely a "cost-benefit" determination by a Chrysler bean-counter to go with the burrito fix.

 

[Talyn]

It doesn't happens after a certain number of years or miles. Happened on new Jeeps as well. However, I am sure injector age could be contributing tot he problem. The issue with misfire on 00-01 Xjs is that when you shut it off hot and go to restart it it misfires and that is what the shield on injector #3 prevents. The other issue is a cold start misfire, that is what the reprogram fixes. Yours doesn't fit the pattern on either. However I have read a TSB on the valves sticking or something to that effect if the engine doesn't see above 3000RPM often. The fix for that is to run Mopar Combustion Chamber Cleaner through the intake to clean eh valves. Seafoam will do the same thing. You could give that a try.

 

[joe_peters]

It doesn't happens after a certain number of years or miles. Happened on new Jeeps as well. However, I am sure injector age could be contributing tot he problem. The issue with misfire on 00-01 Xjs is that when you shut it off hot and go to restart it it misfires and that is what the shield on injector #3 prevents. The other issue is a cold start misfire, that is what the reprogram fixes. Yours doesn't fit the pattern on either. However I have read a TSB on the valves sticking or something to that effect if the engine doesn't see above 3000RPM often. The fix for that is to run Mopar Combustion Chamber Cleaner through the intake to clean eh valves. Seafoam will do the same thing. You could give that a try.

I would also like to mention a couple of items here: elimination of the fuel return from the rail, and the introduction of ethanol, along with a change in the intake and exhaust construction, I believe these all have contributed to the problems in the 00-01 XJs.

I believe the ethanol is contributing to heat soak problems in earlier XJs too.

 

[gradon]

Interesting theory there Joe

 

[winterbeater]

I would also like to mention a couple of items here: elimination of the fuel return from the rail, and the introduction of ethanol, along with a change in the intake and exhaust construction, I believe these all have contributed to the problems in the 00-01 XJs.

I believe the ethanol is contributing to heat soak problems in earlier XJs too.

X2 - Older carbureted engines had a big problem with fuel percolation in the carbutetor when they were shut off hot. And it was VERY bad when any ethonol was used.:flame:

 

[Tall Shadow]

It doesn't happens after a certain number of years or miles. Happened on new Jeeps as well. However, I am sure injector age could be contributing tot he problem. The issue with misfire on 00-01 Xjs is that when you shut it off hot and go to restart it it misfires and that is what the shield on injector #3 prevents. The other issue is a cold start misfire, that is what the reprogram fixes. Yours doesn't fit the pattern on either. However I have read a TSB on the valves sticking or something to that effect if the engine doesn't see above 3000RPM often. The fix for that is to run Mopar Combustion Chamber Cleaner through the intake to clean eh valves. Seafoam will do the same thing. You could give that a try.

It is a strange problem, that is what is throwing me off troubleshooting it. I have a bunch of automotive experience, but this one is a tough one.

I had been going at the problem as though it was an ignition issue, but after reading the troubles that others have had with the injector(s).....I am beginning to wonder if I shouldn't be going down that road.

It doesn't help that It is a bad time job/money wise right now. I work in the automotive industry, for a major automotive industry supplier.....and Our two biggest customers are GM & Chrysler. Needles to say, times in the metro Detroit area are pretty bad right now....so money, jobs, and everything else are pretty shaky. I can not afford to be "Shotgunning" my work vehicle right now. Or to be without it.

Ok....Thanks guys! I will keep at it.
And, I will keep reading this board (thread).
Hopefully someone can help point me in the right direction, or gives me the missing piece of the puzzle.


Tall Shadow :gee:

ETA: Page 4 is Mine!

 

[Talyn]

Joe, how do you activate the cool down timer? I'm trying to think of a way for it to self activate when you turn the engine off.

 

[winterbeater]

Joe, how do you activate the cool down timer? I'm trying to think of a way for it to self activate when you turn the engine off.

They must make relays that activate "ON" when the power is shut off.

 

[Talyn]

They do, but would there be any issue sending constant power to that unit when the engine is off?

 

[joe_peters]

Joe, how do you activate the cool down timer? I'm trying to think of a way for it to self activate when you turn the engine off.

Pretty simple with the timer I linked to. It can be set for a positive or negative trigger. I would use the timer to trip a HD relay to provide battery power to the fan, probably with a diode to prevent feedback.

 

[Talyn]

Why not just use the timer to trip the stock relay?

 

[joe_peters]

Why not just use the timer to trip the stock relay?

Why not! Just put a diode in to isolate the timer.