hey guys,

I have a 97 Xj and i'm at my last nerves here. I had a cylinder 1 misfire for awhile. well i replaced all injectors, cap,rotor, plugs, and wires. well after all that still had a misfire. so i ran a compression check.
#1: 100 PSI (well below requirements)
#2 130
#3:150
#4:155
#5 160
#6:150
well someone at work told me to do a leak down test to which i did and found out my #1 intake valve had air coming out of it. so i got a valve and tore the top end apart. well i found out the valve was beat up. all cylinders themselves were clean not much carbon build up or anything (even after 233k miles on it).the head casting is 0630 (which i found out is one of the strongest heads made). well my #1 and #2 valve seats were slightly pitted but not terrible. so i cleaned the head and valve seats and made sure all the valves were in good condition. took it to a machine shop and the head is off by .0005. so i assumed that was fine. well i discovered a small crack in number 1 but didnt correlate that to the compression problem because #2 had a small minuscule crack. i had them welded and fixed and looks brand new almost.

so i got it all put back together and all valves we're seating correctly. damn thing started right up with only priming twice. only problem is still #1 misfire. i had an open injector harness on #1 and replaced it as well. It sounds beautiful while its running almost cant tell it's misfiring. replaced the crank pos sensor and cleaned out intake, throttle body, iac and everything on the top end. anything that'll help me at this point in time would be greatly appreciated

Richard

 

Since you also have a `97, strongly suggest you inspect the injector harness before anything else.

Here's my original photo and you can make out the fuel rail mushed into the wire harness:


This closeup makes it very clear:


Simply moving the wire harness from this pinched location eliminated my high speed misfire. If that harness is touching the engine anywhere, not just the fuel manifold, look very closely.

 

i have actually done that. i heard that from a jeep guy at work. all the injectors are ticking as they should. appreciate it

 

Need new compression numbers. Let test data lead the way here.....

 

working on it. as soon as i get new ones i'll let you know. but it'll be saturday probably

 

Your '97 is affected by the valve spring TSB. Considering all you've done, I would replace the valve springs on cyl 1. It fixed the misfire on mine.

 

http://www.cherokeetech.com/VBull/sh...LINDER-MISFIRE

 

cruiser, that TSB is for exhaust valves not rotating. The one I'm thinking of was for '96-'99 4.0s, and talked about using Mopar CCC and replacing all the valve springs. Since the OP had his head apart, I'm assuming he has cleaned it, and can skip the CCC, and just replace his springs on #1.

 

Gotcha.

 

well i appreciate the input guys. and yes my head was entire cleaned when i had it apart including valve springs. but my misfire is constant at all rpm's not just the high ranges. and i work at a machine shop and checked everything on the head including squareness and diameter of the valve springs.

 

also have to remember that TSB is for 1999+. probably because of the 0331 head casting which was total crap.

 

Like I mentioned earlier, there is a TSB for '96-'99 for a misfire caused by weak valve springs. I swapped out the springs on cyl 1 on my '98 and cured a misfire. The springs look perfectly fine (squareness, etc), but are weak. If everything else checks out...

 

well appreciate belvedere, i'll look into it. i just dont want to keep throwing money at it. so far i'm up to $850.

 

you guys are gonna get a huge laugh out of this.. I fixed my misfire. how you ask? when I tore my head apart got it all back together I obviously pulled my battery out. Well I reconnected it when I got all of it back together. still had a misfire right? Well I had a wild hair up my *** to disconnect/reconnect it again. problem went away and started firing on all cylinders. must have detected a misfire when it was burning all that crap I cleaned out. Weird, but works :P