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88 XJ 4.0 Serious Engine Probs & ???

Tom_W

NAXJA Forum User
Location
Tamaqua, PA
My wife's 88 XJ with a 4.0 has been running rough lately, and today it was severe, so when she got home from work, I decided to give it a tune up since it was overdue for one. Well, the tune up didnt help, however I did determine there was no compression on #4 cylinder. When I pulled the plugs, it was all covered in oil, so I did a comp. test and zilch. I blew air into the spark plug hole, and lo and behold, I had air coming out of the dipstick tube. So I am assuming either it has a hole in the piston, or the rings are totally shot. Oh, yeah, it gets "real good" oil pressure now, like pegs the needle instead of running 50 - 60 psi. No water in the oil and runs at normal temp. Since she was using it as a daily driver, going 20 miles to work, I told her to take mine (which I just replaced the engine in last month). Anyway, I was thinking of taking the push rods and lifters off of that cylinder, to keep the valves closed, and not let raw fuel into the oil, or a mixture of oil and fuel out the exhaust, and running it 3 miles back and forth to work for me until I can get another engine to put in it, hopefully in a week or so. Any comments or suggestions are more than welcome.
 
You said that the plugs are oil soaked, which to me would lead to bad rings or valve guides. I blew a head gasket on my old Chevy 350, replaced it and it started smoking like a son of a bitch when I got it back together. When I finally tore it down for a rebuild, I found that the oil ring had broke in 3 different places, and one of the others had broken too. I still had comp. in the #8 hole, the one that was blowing all the oil by. Also when I was honing it out, it was the most worn hole. The valve guides were also worn on a few other vavles.

Take off the vavle cover and watch to see if the int+exh vavles move. If not, look for a flat lifter, broken vavle spring, ect. Havent seen a 4.0 do that yet tho.

If your planning on replacing the motor, tear it down to see what it was, and let us know.
 
OK, do a "dry" compression test and then a "wet" compression test - the difference is the addition of about a tablespoonful of fresh oil down the spark plug hole. It's best to do a compression test on a warm engine - for two reasons. 1) That's the condition the engine runs in. 2) You'll hear it run for a couple minutes, and that gives you a baseline for how it should run after you're done.

Check the oil pressure sender - if the needle is "pegged," you might have lost a connection, or the thing might just be "stictioned." Reconnect or replace (you'd be surprised how often women will pay attention to gages - my wife is after me to swap a gage cluster into the other 89... The upside? She's saved me hours in troubleshooting...)

If you have access to a borescope, it would not be a bad idea to snake it down the throttle body, and look at the back of that intake valve. If it's oily, it's the valve guide seal - and you can change them without pulling the head (put each cylinder to TDC compression, apply air pressure to the cylinder through the plug hole, and pull the valve springs. The positive style valve seal is easy to change - once you have the spring off.

Please note that you can have good compression numbers, but still get oil fouling from the crankcase - the oil control ring is not a compression seal, and if it fails, the compression rings will actually start to "pump" oil into the chamber as a part of normal operation.

That's all the thoughts for the moment. However, I do think that valve guide seals fail before oil control rings...

5-90
 
"Anyway, I was thinking of taking the push rods and lifters off of that cylinder, to keep the valves closed"

just a tid bit, you can't remove the lifters without pulling the head.
 
sorry, I meant rods and rocker arms

But, I searched around today and found a bunch of engines all around 300 to 400 dollars, so that is my project for next weekend
 
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