dferrel

XJ 4.0 200k started out as full blown miss only when idling. now it comes and goes cylinder 1 misfire cleaned throttle body inside and out iac ran seafoam through brake line (intake) i've done all this at-least 3 times changed plugs wires dist cap rotor bug someone said injector. changed injector no change,took it back took to another mech he did fuel pressure check lost 20 psi in 5 sec changed fuel pump assem did good until you accelerate hard miss comes back I did a compression check and #1 is 50 rest are 150. I read a tech serv bulletin says change valve spring and ??? clean combustion chamber let sit 2hrs drive in 1st gear to 4500 rpm hold for 15 sec then repeat again it actually works. until you have to throttle hard again. If I drive normal, easy it will stay running good for awhile. Does it really need a head job or something because it runs and idles great when it wants. I have alot more but thought this was enough for a first post thanks Dale

captainwoot

Carbon build up and non rotating exhaust valves (tsb) can cause an intermittent misfire , I would try the Crysler spay can of combustion camber cleaner( follow the directions on can) a couple of times. If that doesn't help then pull the head and sent to the machine shop.
Good luck!

youdid check and make sure there was no vacumm leaks???

josh77

you have to find out what is causing the loss of compression. you need to pull the head, inspect the head gasket, head and block for cracks/damage. check the valves for damage(burnt/sunk). do you have water in your oil? it will look milky. i havent looked at that tsb yet but that would be a good thing to check as those tend to come out for comon problems. good luck.

brutalxj

If you have the time pull off the head and inspect everything. My guess is you need to re lape all the valves intake and exost. Sounds like one is sticking under a load.

dferrel

Cant find any vac leaks. I also did the water through the intake brake line. didn't smoke a bit but I've cleaned everything so much I didn't figure it would I also ran bg in the oil for 15 min. then changed immediately thanks I'll give it a try.

dferrel

re checked compression on cyl 1 when running good 100 first try 102 second try my mechanic asked me again today about leak down test so I searched how to and tried it not sure if I did it correctly but I had some coolant come out of radiator?

captainwoot

If you were applying air pressure to the cyl and it forced coolant out of the radiator you have a cyl head/ and or gasket problem. Time to pull the head and get it checked.
Good luck!

Rmart30

top off the radiator completely and if ya got air bubbles coming out of radiator when doing the leak down test its time to pull the head for sure.

rich

At 3200 rpm your valves will start to spin.If you want to run it that high and have someone pour in seafoam or bg44 then try it than pour in more and let it soak. Way back when they used to shoot in a little water for a bit and that really broke any carbon build up down.Or use the chrysler spray that the CAPTAINWOOT said.

warthog

Has the engine ever overheated?


I would be willing to bet you have a crack in between the two valve seats in the number 1 cylinder. Drain some coolant and let it sit for a couple hours. Then look at the coolant for an oil sheen on top. Let us know

Check out these threads of mine from a while back

https://www.cherokeeforum.com/f2/cyl...misfire-47810/

https://www.cherokeeforum.com/f2/cyl...-update-54529/

dferrel

thanks for all the help I'll be getting off a couple hours early today so I will be working on the jeep. 1998 jeep cherokee XJ I need to re name it time consumer. I love it tho its a lot of fun and look at all the new expensive things I'm learning along the way.

dferrel

ok either i'm insane or just don't know what ~~~~I'm doing I did another compression test in cyl 1 and it was 125? when I first started month ago it was 125, then 60, then 90, and today 125 is that normal for it to fluctuate. so while I was doing another compression test I re-did leak down test took rad cap off put breaker bar on crank and rocked it no air bubbles came out rad just pushed water level up a bit. all I can hear is air escaping from throttle body bore when it rock it it gets louder as piston is moving. so I'm leaning towards the post were he said at 3200 rpms valve spins because that's about were when you throttle hard the miss will appear so my guess is when it stops spinning its not seating until i do 1st gear at 4500rpms for 15 sec to re-seat it. So were should I go from here to correct this annoying random rough idle?