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Compression test results

4K views 14 replies 6 participants last post by  Nubby55 
#1 ·
94 2.5L has been running terribly. #2 cylinder not firing. Has fire, has fuel. Ran compression test and here are the results:

#1 Dry 110psi Wet 130psi
#2 Dry 40psi Wet 40psi
#3 Dry 70psi Wet 90psi
#4 Dry 60psi Wet 80psi

Jeep ran fine after I replaced the head gasket and then bam, #2 just quit firing.

Where do I go from here?

Thanks.
 
#3 ·
When you replaced the head gasket, did you machine the head? All of those cylinders look bad, it looks like you have a head gasket and piston ring issue. Run a leakdown test to see where it's actually leaking.
 
#5 ·
You need another tool and an air compressor. There are videos on it. I have a writeup in the general forums for how to make one for cheap. What kind of compression tester do you have? You need the standard air compressor fittings for this to work.
 
#6 ·
From what I see in the numbers Dry vs Wet, I would think head gasket or Valves, and not bad rings, as low as the wet numbers are the ring maybe OK, and it's leaking by bad valves or Gasket, if bad Rings when you seal them with oil the numbers should Jump way up.
 
#7 ·
#1 ring just looks a tiny bit worn. Hopefully it was just a bad head gasket job and it needs a new $20 gasket and machine job. Leaking valves and worn piston rings are not as fun.
 
#8 ·
I turned the crankshaft after head was back on and all valves appeared to operate. Against my better judgement I did not have the head machined. I definitely had a bad head gasket, so I talked myself out of having it checked. I knew it was a bad idea when I did it. The thing I don't understand is how all of a sudden it started running bad. It ran great for awhile. Does this info change anything I should do next?
 
#11 ·
You already know what to do.

1)- Pull the head.
2)- Pull the valves. Keep the valves in order.
3)- Send head to machine shop.
4)- Replace any bad valves then hand lap all old and new valves.
5)- Check the block deck with a mechanics straight edge and a feeler gauge.
6)- If the block deck has only a slight warp, you may consider using two head gaskets. With the head being machined the second head gasket may not reduce compression ratio too much. If the block has any out of spec warping the recommended repair is to pull the block and have the deck machined.
Two gaskets is an old time work around. I recommend machining the block if it's even out of spec a little, but there is a degree of practicality that only the vehicle owner can determine.

You should have a Factory Service Manual. I bet it will give you the specs of tolerance on the head and the block deck.

You seem to be a competent mechanic, but any one of us can make a mistake now and then. The issue may simply be an error during torquing or a faulty or damaged head gasket. In any event, you will need to pull the head.

Keep us posted. Good Luck, L.M.
 
#12 ·
If this was My Jeep i would pull the head and that the whole thing to Shop for rebuild.
 
#13 ·
Everybody above is correct and offers sound advice and explanations. This is what you should do.

To answer your question about leakage, you don't necessarily leak coolant or oil on a blown head gasket. It all depends on where it is. It sounds like you simply have an air leak, letting compression leak out of the cylinders.
 
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