Hello everybody
OK, I know my jeep is messed up, but it runs and I enjoy it day after day despite all its little problems.

Fluids / wires/plug/rotor. distributor cap and plugs are new
Jeep laredo 89 200K miles
Noisy engine that is knocking

Yesterday I decided to do a compression test. Granted I have never done that before, i followed instructions on the Haynes book that were confirmed in this forum. Throttle open, wire coil grounded to the engine block and fuel pump relay disconnected, 7 strokes

Here are the results:
pressure max at first stoke for all of them
#1: 60 plug looked clean
#2: 60 plug looked clean
#3: 60 plug looked clean
#4: 58 plug looked clean
#5: 35 plug had some soot on it
#6: 30 plug had soot mixed with oil deposit.

This is my interpretation: OOPS
They are low (120-150 according to the book) so this is not good. % and 6 are really low compared to other so maybe a blown head gasket but there is no coolant in the oil (I changed it and collected in a clear bottle).
The jeep is running fine, I went good on the Highway up the hill and felt more power than in my other car and had no pb maintaining a 60mph speed in 4th gear up a 10%grade hill.
Jeep doesn't smoke either, not losing oil or coolant.

I am trying to learn and fix by myself things (no prior experience)

So what do you guys think ?
Am I retarded and the readings are low on 1-4 because I didn;t do it properly but still have a problem with 5-6 ?
Can 5-6 cause the knock ?

It's possible to blow the gasket between cylinders and not have it intersect an oil or coolant channel. In which case you'll get the low compression between cylinders with no apparent oil/water mixing.

The soot on those plugs could be a side effect of that, incomplete burns due to low compression. Or the soot could be the cause, there may be buildup on the valves leading to them not sealing correctly. Try seafoaming it and see if that helps at all, and put new plugs in 5/6 at the least.

thanks for the advices.

Should I be worried about the 60psi reading on all the others ? Or is it just my inexperience combined with a "rented" tool.... As long as they are consistent then I should feel OK ?

I have read a lot about seafoaming, and I did use it in the gas tank. Tried in the brake booster vacuum line and didn;t get any smoke, tried in the crankcase and within 5 minutes I had a major knock that started (got scared, turned off and flushed the oil right away lol)

So anyway, what would be the best location for seafoam to rech the #5 and 6 ? Directly into the Throttle plate or cranckcase ?


PS I like your signature.... taken from a picture that is my desktop picture too

Honestly I think you did the test wrong, if I'm reading correctly you just did one revolution of the engine? I've always been told that you should crank until the compression stops building quickly, like 5-6 revolutions, on a warm motor. I think you'll get better numbers across the board if you do that, but you may still be low on 5-6.

When you did it in the vacuum line, did you do it like the instructions suggest where you let it stall the engine then let it sit for 15 minutes?

How much did you use in the crankcase? Sounds like you may have used too much and thinned the oil out.

Thanks, I like that quote.

No I did just like the book said (doctus *** libro ) warm engine (damn hot plugs), screw gauge in, turn the key and I listen to 7 revolutions then off. Gauge went to about 55 the first revolution, then pressure built up slowly to about 60. I was watching the gauge and the needle kept bouncing a bit up everytime untill it reached about 60. I did the test twice for each and got same results.... but since I am a slow learner and take a lot of time to do things, maybe the engine had time to cool down too much who knows.

Yes i put the seafoam slowly in the intake when warm, and let it stall... waited 15min and started again, revving the engine at 3000rpm...
For the cranckcase, I don;t remember how much I put, but it was about 1/3 of the bottle
This being said, i am not 100% sure I did it right either....

Anyway, I appreciate comments. anything can help me get better

So assuming low compression on 5 and 6 is a blown head gasket... would I be able to see it if i remove the valve cover and redo the gasket ?


Byt he way you live in a nice place I lived 3 years in Gainesville and Middleburg

Those #'s are pretty low for one that is running good with "more power" as you say.

Could be a bad gauge and i think id ck it with another one to verify the #'s.
If they verify that low and were going to do a head gasket replacement like you asked about it would be wise to go ahead and re ring it at the very least.

Thanks for the insight....
yes this is what i didn;t get.... the car has enough power to do a burnout start if I don;t pay attention to the gas pedal ;0 and was not consistent with low reading. i might try again with a different gauge, good idea
Yep the idea is to wait until winter and take the engine apart... to learn and of course change what needs to be changed I guess