blown head gasket?

91 xj 4.0l HO MPI

Well the jeep is giving me fits at this point.

About a week ago it was staring to loose power when driving, then it started having problems staying lit at idle. now it runs very ruff, almost no power when it's warm.

I was suspecting a fuel problem. cheched the vacuum, and pressure regulator, looks good. Replaced the fuel filter, no change. looked at the fuel pump, the screen looks fine as in no clogs. The pump seems to be running ok, but i don't have the tools for a pressue check. it sounds like its working the way it allways has.

tore the throttle body apart and cleaned it, ckecked all the electronics, they seem to be working or within spec of the jeep service manual, and sugestions here.

did a compression check

1 94 psi
2 123 psi
3 123 psi
4 100 psi
5 100 psi
6 123 psi

alt here is about 5200'

do these numbers look normal? i know the 1 is a lot low and 4,5 are low

the jeep is not blowing smoke out the back when running. and the problem gets worse when it is running at normal temp. Also this jeep has allways had problems with overheating. it now has a 2 core radiator the seemed to help for a while.

Sounds like head gasket to me, are you losing coolant or have coolant and oil mixing?

Do the test again, this time squirt about 1oz of oil in each cylinder first.
The test you posted is only 1/2 a compression test.

what does the oil do?
I would like to know how healthy the block is.

Also i found that the problem was the fuel line in the tank wasn't right.

buy not right i mean wrong size, clamps wheren't on correctly. Fixed that and bingo jeep runs fine.

XJhammer said:

what does the oil do?
I would like to know how healthy the block is.

Also i found that the problem was the fuel line in the tank wasn't right.

buy not right i mean wrong size, clamps wheren't on correctly. Fixed that and bingo jeep runs fine.

Click to expand...

If the oil causes a large increase then the compression rings are shot.
If they is no increase then it's a valve issue.

Adding oil turns it from a "dry" compression test to a "wet" test - and helps to highlight compression ring problems. After you're done with the test, have all the spark plugs out and crank for 10 seconds or so to blow the oil out of the cylinders.

Doing a "wet" compression test usually yields the following results:
No Change - compression leak is in the valves or head gasket (more in a minute.)
Improved Compression - compression leak is going past the compression rings, and a re-ring is indicated.

If you don't get improved compression with the wet test, then you'll want to get an "air hold adapter" that screws into the spark plug hole, and then connects to an air compressor. Run the cylinder under test to TDC compression, and then supply air pressure (up to 100# should be fine.) Then, take your ear around and listen for air noises.
Throttle Body - compression leak is past the intake valve
Tailpipe - Compression leak is past the exhuast valve
Radiator Cap - Compression leak is in the head gasket, between the cylinder and the cooling jackets
Oil Filler Cap - Compression leak is in the head gasket, between the cylinder and the oil return hole/lifter gallery

How's that?

5-90