Hey guys,
I'm looking for a little help with my 91 xj. First i'll tell you what its doing then i'll tell you what I have already checked and done to the motor. (also for the record, my jeep is just for wheeling only)


Over the past year my jeep has had problems of backfiring when revving. In fact you cant hardly rev it up past 2k rpms because of this problem. The funny thing about the backfiring problem is that sometimes it does it, and sometimes it runs great. So a few weeks ago I went wheeling with some buddies and my jeep started off running fine (no backfiring) which was great! After a few trails and when I guess the engine got up to normal running temperature it shut off as if someone had just turned the key. The jeep would start back up after about 5 minutes and run as normal again then shut off again.


So with what was happening I figured it would be the crankshaft position sensor, or the coil pack. I replaced the crankshaft position sensor (duralast sensor) and nothing changed. I also replaced the coil pack with one I already had from a parts jeep and nothing changed. Actually it even ran worse... backfires more and is hard to start. so here are the things ive checked.


-I've checked the coil plug wire to the distributor and I am getting spark to the distributor. I also checked the power to the distributor and I am getting 10.4 volts while cranking.


-I checked each plug wire and I am getting spark throughout each.


-I checked fuel pressure and it is reading 32psi when running and 49 when the vacuum line is disconnected.


-after checking the fuel pressure I soaked my fuel rail and injectors in sea foam after seeing the fuel that came out of my fuel rail was brown. This did nothing.


- Lastly, I replaced the fuel filter and I ran sea foam through the throttle body and it did nothing.


I think the backfiring problem/and the shutting off at running temperature are two separate problems.


Any help would be greatly appreciated guys, I don't know where to go from here. thanks,

 

Sometimes crank sensor needs to OEM , and have you checked the valve train it could be a broken valve spring or the cam going flat .

 

 

What are the fuel pump specs? There's usually a 7 pound spread from vacuum tube connected and then disconnected. Not 17 PSI.