Compression #'s not consistent... bad?

[///MptyPockets]

The car is a 96' M44 with just about 170k on it. I've never done a compression test and was just curious what the readings were so I did a test today.

I dont think the headgasket is bad -- no white smoke, no oil in the coolant, and no coolant in the oil, oil cap looks good.

1 - 200psi
2 - 185psi
3 - 120 psi
4 - 110psi

Would the results differ at all if the car was on a slight incline? Any thoughts?

Thanks in advance,
Derrick

[jca]

Does the car have starting or driveability problems? If it doesn't I would be tempted to leave well enough alone, although obviously the differences between cylinders are significant.

[tiFreak]

Originally Posted by ///MptyPockets

Would the results differ at all if the car was on a slight incline? Any thoughts?

I wouldn't imagine that it would, and even if it did I doubt it would cause almost 100 pounds difference between cylinders 1 and 4


if you don't feel like dealing with it I'll buy the car off you

[///MptyPockets]

No issues starting or running whatsoever -- I just wanted to do a test out of curiousity because it's getting up there in mileage. I was going to do a small tune up (plugs, wires, infamous plastic coolant conectors, VC gasket, tstat, maybe the water pump) and before I ordered parts I wanted to do a compression test to make sure everything was tip top. I'm a bit surprised at the results because like I said the car runs great and has been the most reliable car I've ever owned.

tiFreak, I actually considered selling it because I just purchased an ml350 -- but I'm not sure if I can part with it lol. I love the ti man. You'll be the first to know if I decide to though.

Thanks for the feedback. Do you think the difference in cylinders is something to worry about or does it call for a leak down test?

-Derrick

[xxxJohnBoyxxx]

Something on that test was wrong. I have never seen a stock M44 with a 200psi cylinder.

You would need race gas to run that high compression.

220psi required 110 octane race gas

Warm engine. remove all plug wires. pin TB open and do test again with plugs in all cylinders but the one you're testing.

Maybe do a Seafoam before the test to knock off a carbon in there...

John S

[tiFreak]

Originally Posted by ///MptyPockets

tiFreak, I actually considered selling it because I just purchased an ml350 -- but I'm not sure if I can part with it lol. I love the ti man. You'll be the first to know if I decide to though.

really? I was just being a smartass I am looking for a second ti though so if you do sell I'll probably buy it off you

[Tom D]

the numbers are not important, but they should all be within 10%.

a incline won't change anything.

i think you need to do it again. it sounds like user error.

*engine dead cold

*remove all the plugs, leaving them in just stresses the starter and doesn't change the results.

*throttle plate wide open

* crank engine through a certain amount of compression strokes, lets say 5.

*do the same thing on every cylinder with the same amount of strokes

*warm up engine

*repeat the above

if you still have 2 cylinders more then 10% lower then the highest, then;

*add a tablespoon of oil into that cylinder and re-test.

*if the pressure comes up, then the rings are worn.

*if the pressure does not come up, then do a leak down test.

[bullmand]

I would add making sure the battery is in good shape to that list. If the battery's getting weak halfway through testing it might affect the results.