hello,im new to the forum but not to the world of xj's. i have a 1992. i have been experienceing problems with it and cant find any answers anywhere else. it starts and runs great...for about 40 minutes...then it starts to cut out and stumble then dies.(doesnt matter if im driving or its idling). it wont start unless you let it set for about 20-30 minutes. i have replaced the cps...2 times now thinking i had a bad one. i have replaced the coil,because it looked to me like the spark was more orange than blue....even with the new coil it still looks the same and still shuts down. i just now realized that the distributor is from a renix jeep(dont ask,it was done before i got it). the jeep is getting plenty of fuel in the rail(no i havent done a pressure test). what am i needing to test...i tested the input to the coil,im getting 11.84 volts...the resistance from the ground to the primary on the coil is12,300 ohms. when it shuts down and wont start,it is still getting spark,thats what throws me off. any help is greatly appreciated.

 

possible the ignition module?? i know at work to test em we have to test them 4 or 5 times to let them warm up to get an accurate test.. maybe yours is failing when it warms up? then once it cools down its good to go again.. just a thought?

 

I'd say vapor lock, but that's impossible...

 

how do i test the module? and will it cause a problem with it being a renix in a H.O. ?

 

electric module in dist getting hot ever replace it

 

when hot you getting spark from spark plug wires

 

yes it still gets spark even after the jeep goes into default and shuts down. it will turn over just doesnt try to fire. then after it cools it will start and run again. it happened before,thats when i changed the crankshaft position sensor....it worked great for about a month...then started screwing up again. so i changed the cps again thinking it was bad....it still does it.

 

if you getting spark at the wire after it shuts off pour a little fuel into top of throttle body not a lot just a liffle if it startys fuel pump is getting hot and locking up

 

but like i said...when it shut down i checked for fuel in the rail and it had enought pressure to blow fuel all over my hand....if the pump quit wouldnt the rail have no real pressure? all i know is that its running me nuts,i dont have money to throw at it and i really need this jeep fixed.

 

gotta start some where

 

I might agree, there will still be pressure at the rail even though the fuel pump is stopped.. Might not even be the pump but the fuel filter getting clogged. but like free mentioned need to start somewhere and if its cranking and getting spark at the cylinders than that would me theres no fuel...

 

 

I would say ur O2 sensor. When u first start ur jeep its in an open loop untill it reaches temp then it uses the sensors to adjust fuel-air-and spark. U can just pull out the O2 and spray it with brake cleaner and shake it a lot to clean out all the carbon build up. My second thought would be the MAP sensor on ur fire wall. My third would be the connection on ur coil. When its running wiggle it around. With age the pins can ware down enuf to not always get contact. And u need the rubber thing on the plug to get appropriate contact. That's were I would start.

 

all these are helpfull hints,thank you. one thing i forgot to mention is that it runs almost exactly the same amount of time each time it dies...almost exactly 40 minutes. i guess i will have to check and see if i can rent a fuel pressure tester and check that. how do i check the MAP sensor? and i guess i will also try and pull out the oxygen sensor...even though that dont look real sweet to do.

 

I can`t tell you what`s wrong with your XJ but as someone who took 2 1/2 years trying to fix an similar odd electrical problem I will tell you to look "outside the box"...You will find that on an XJ engine that 2-3 or even 4 different items and sensors will eventually share a common ground wire or even hot wire. For example the MAP sensor, TPS, coolant temp sensor and CPS all have a black/lt blue ground wire coming off and they then combine as one inside a heat shrinked union along the fuel rail. Once they combine it continues as a single wire. If you have a problem affecting several seemingly unrelated items try and follow the wires and see where they combine. NOW.....Here`s where my experience may be similar:

My XJ did the exact same thing..It would run great for a certain period and then ..bang..run like crap. What I eventually found out after the mentioned 2.5 years is that the TPS and the MAP sensor both have a violet/white wire coming off of them which join in one of those heat shrink things and then continue on as a single wire to the computer. What had happened in my case was that this hard heat shrinked piece had been bent and dried up and cracked inside so the wires werent doing what they were suppose to as far as transmitting the signal and when the MAP sensor picked up a change in the air pressure and would send a voltage signal to the computer this went instead to the TPS and the TPS sensor would then read this new voltage and try adjusting the gas/air mixture and the engine would start acting oddly until it cooled down enough.

In your case i would try and determine what items might activate or send a signal at the 40 minute mark and then see if those items and something else share a common union.