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Engine trouble, help me out guys

YosemiteJeeper

NAXJA Forum User
Location
California
I took the Jeep ('91, 4.0) to a shop to see why it wasn't cooperating with me, and I walked away with the knowledge that I have a dead #1 cylinder and he recommended a new engine. I had a compression test done a while back, and #1 & 3 where low. I have new plugs, wires, cap, rotor...its getting spark and fuel. Its just not firing it off, its throwing it right out.

Does anybody have any thoughts on this one? Thanks
 
I am understanding it is spitting out fuel?

If so, you have intake valves open at TDC of the compression stroke--what professionals refer to as "really bad JuJu!"

Bent valves. Valves covered in carbon. Bad timing chain. Timing chain gear locating pin sheared. Those are some of the things you are facing. Did you do a "wet" compression test to check the condition of the rings?
 
intake? wouldn't it be exhuast? cause it was throwin it out the exhuast and reading on the smog. Another thing I thought of: it was reading fine at 2500 on the test, but I can hear noise again at ~3000+rpm. I think theres a range where it works, not sure. Interesting though haha
I was thinking of looking in the valve cover to see whats there. I wanted to stop by the local pick 'n pull this weekend too and look for a engine to drop in.
 
It's possible for an engine to read falsely low on compression if it has an ignition problem. The unburned fuel will wash the walls and cause the rings to lose their seal. If there's indications of a plug not firing, AND a wet compression test brings the low holes up to spec, there may be hope for the engine.
 
intake? wouldn't it be exhuast? cause it was throwin it out the exhuast and reading on the smog. Another thing I thought of: it was reading fine at 2500 on the test, but I can hear noise again at ~3000+rpm. I think theres a range where it works, not sure. Interesting though haha
I was thinking of looking in the valve cover to see whats there. I wanted to stop by the local pick 'n pull this weekend too and look for a engine to drop in.

You are spitting raw fuel out of the exhaust? Doesn't matter, if you have a valve open on the compression stroke, intake or exhaust--one each for each of the 6 cylinders in a 4.0, then the fuel charge is going to be pushed out, not compressed and successfully ignited. Is that clearer for you now?
 
After you do a "dry" compression test and record the numbers for each cylinder, you shoot a little oil in each cylinder and test the compression again. If you see a large jump in compression wet, then the problem is worn rings/piston/cylinder, no increase indicates burnt or bent valves, hole in piston.

A leakdown test allows you to listen for compressed air--intake manifold = intake valves, exhaust manifold = exhaust valves, crankcase = worn rings/hole in piston.
 
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