I have a 1998 Jeep xj. Last night coming down the trail in four high riding my brakes I lost throttle response and the Jeep died. I managed to get it running and drove it home. The next day I fired it up and got a code for a misfire in cylinder two. I checked the fuel pressure on the rail it was 50 psi, however as soon as the the car was shut off the pressure fell. Is this related to the miss fire? Any tips ?

 

It's possible you have an injector that isn't shutting off completely and adding fuel into the intake manifold when it's supposed to be turned off, leading to a rich mixture when that cylinder does fire. It can also be carbon on the intake valve seat not allowing it to seal completely at idle, but run normally above that. That can be cured by slowly pouring a glass or 2 of water down the throttle body while holding the throttle open at about 2000 rpm. It's called a "steam cleaning." You can use stuff like Seafoam, but water works fine and it's cheaper!

However, the sudden loss of fuel pressure at shutdown points to an injector.

 

Changed the injectors on my 98 because I had a poor (stumbling) idle. More precisely stated, it had a lope where it seemed that there was an imbalance of combustion across the cylinders. It was like one or more cylinders was receiving more fuel than the others causing the power imbalance between cylinders. After much fussing with it I finally changed the injectors and that cured it. You can find a thread on it here as it occurred within the past week. The difference in running before/after the injector change was so dramatic that I bought another set and replaced the injectors on my 96, my daily driver, this morning. It ran pretty smoothly before the change and now it's even better than that. I guess we all think that if an engine is running it's all good but despite the fact that these 4.0's can seem bullet proof the injectors may, in truth, need to be replaced after 150,000 miles.