• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Cracked header cause bad compression?

gradon

NAXJA Forum User
Location
DC
So my roommate has a 97 country that's been temperamental with it running well and not. He's gotten low MAP input CELs before and has swapped out two different JY maps and 1 new map. I tested the supply voltage and it was 4.9xV and also did a continuity check on the three wires to the PCM--all tested good. Anyhow his latest issue was a cracked header(due to cracked MM) and he said smoke was pouring out of the crack. He bought a nice polished APN knockoff and installed it last week. He said it ran great for a day and then it started to smoke again. The smoke is from unburnt gas. Now while we had the rail off, I had him cycle the ignition a couple of times to see if any injectors were leaking--none were. Also, we noted that the #2 port in the intake manifold and in the head were clean and didn't have any carbon/junk buildup the other cylinders had. Today while the Jeep was running--rough as if one cylinder isn't working--I unplugged the injector harness of each cylinder to listen for a change: only unplugging cylinder 2 didn't change the rpms. We pulled out the spark plug and verified the orange spark(not blue, but same spark that other cylinders have). We used a new wire and plug with the same effect. There is gas in the oil from some culprit. Is it possible that his crack in the header was so bad that the pcm added enough fuel to destroy the rings and therefore the compression in cylinder 2? I have a comp tester at my brother's house but am curious cause I've never read of something like this happening.
 
Since the Orange spark on the spark plugs didnt change after replacing the plug and wire have you considered a weak coil?
This would give poor performance, rough idle and the orangish spark you observed.
When you disconnected the injector wires and observed no change on No. 2 cylinder; is the injector spraying when pulsed by the PCM?
If you are interested I am selling a slightly used set of Precision Injector fuel injectors that are designed for 96-98 XJ 4.0L.
 
Back
Top