95xjwhite

Hey guys I'm needing some help here. I have a 95 XJ automatic. I bought the Jeep with a blown headgasket. Sent the head off and all's good got it back together. Now I have this miss at idle. I have been working on this thing for weeks. I have checked/replaced just about everything you can to make this thing run. No check engine light what so ever. Jeep is running very rich run you out of the shop. Drive it down the road it's got loads of power. No blow by at all. I've narrowed it down to clyinder #4. I have spark. I have power and ground signal from PCM to that injector. When I unplug that injector or spark plug wire to that cylinder the motor doesnt make any different sound as opposed to the cylinders when I do that to them. Spark plug isn't wet. I can not figure out why #4 cylinder is dead. If anyone has any more ideas I'm all ears. I'm stumped on this one.

95xjwhite

Nobody???

JeepRunner5

When i bought my 93 jeep it was often miss firing and just turned out to be cheap crappy spark plugs. Have you tried looking at them and seeing how bad the are? Or Try replacing them all and then see?

95xjwhite

Ive replaced them all with autolites. Which I've read a couple post on here saying switch to OEM champion plugs. I may try that. I've checked the spark on them and it's not a good blue spark but a yellowish orange spark.

nujeepguy

i put reworked heads on a v8 once,had no compression on one cyl. misadjusted valve. are yours adjustable, just a guess

95xjwhite

Valves aren't adjustable. I've checked torque on the rockers twice

jordan96xj

You should be able to visually inspect that the spark is present/good at the #4 plug (have you done that yet?). If that is good, then my next suspect would be the injector. It could be a bad injector even though it is getting voltage and ground command from the PCM. They are just like relays, and can fail mechanically. If both of those were verified good, then I would think there is a valve problem or other compression problem on that cylinder.

95xjwhite

I have checked the spark on cylinder 4 and it's getting a spark. I just replaced all 6 injectors that are brand new. I just put head back on couple weeks ago because of the blown headgasket and had all new valves and valve guides put in. Compression is a little low across all my cylinders even after the new headgasket. Motor has 300k miles on it but I have zero blow by so rings shouldn't be bad

jordan96xj

I guess another next step is to swap the #4 injector with one of the good cylinders and see if the problem follows it. I know its brand new, but we still need to verify that it is functioning properly right?

95xjwhite

I took number 4 injector wire and put it on number 3 cylinder and it followed that cylinder

Motojunky

to clarify: When you move the wire from injector 4 to injector 3, which cylinder does not fire?

95xjwhite

When I move injector wire 4 to number 3 then number 3 cylinder doesn't fire. I messed with it some more today. I think I have a cracked/ broken piston skirt. Took a camera down in cylinder 4 thru the spark plug hole and the side walls are sqored and I only have 70lbs of compression

Motojunky

Sounds like you have a couple of things going on. Have you put the #3 injector wire on #4 yet? What happens?

Even if you correct whatever is preventing power to the #4 injector wire, 70lbs of compression is an issue. Could be that something didn't go right with head gasket change. Could be that something wasn't done right with the head work and a valve isn't seating properly. Could be related to the cylinder damage you are seeing. Could be a combination of items.

I know that's not much real help, but you'll have to rule out all of the possibilities.

jake92

So a couple of things:
1. If you swap components and it follows, then you know your issue is there. So injector wire 4 has an open or short. Time to test the wire and see what the issue in the wiring is.
2. Compression on a theoretical 4 stroke engine (lawnmowers to the biggest gas engines) is bare minimum 100 PSI. The Jeep requires more than that obviously.