first compression test....numbers

[wises4057]

so i just ran my first compression test on a friends eclipse this evening. here are the numbers i got at WOT(from air filter side to timing side), the car was warm.

155-140-120-165.

now, i didnt pull the MPI (MultiPort Injection) fuse because that wasnt listed int he compression test walk through i had, but i see Vfaqs says to do that. i dont know if that would change my compression numbers. The other thing, the compression test walk through i followed said just to pull one spark plug at a time as you do the test, and the vfaqs says to remove all the spark plugs....again...would this skew the numbers?? if not, what do you think, head gasket going out on that cylinder?(there is a light amount of white smoke coming out under a decent acceleration, but not enough to really worry about, and not very noticeable at that)

 

[JStrateger]

Yeah, that definitely sounds like the headgasket is somewhat blown. A good test to do before you tear everything apart is put some oil in each cylinder right before you do a compression test, (tablespoon maybe) if it raises your compression on that cylinder, the piston rings need replaced as well so you might want to tell your friend just to drive it soft until be can afford tondo all the work at the same time, then start taking it apart.

Give this a read, it should help you out and answer any questions you have:
http://www.jspecauto.com/files/jspecautotechcenter9a.htm

 

[wises4057]

alright, cool. i'll have to try that next time i swing to his place. leaving the injectors powered up(not pulling that fuse), and leaving the other spark plugs in while doing the test wouldn't affect each individual cylinders then?

im thinking it shouldn't be rings...his car has always been stock and is between 80-90k miles.

thanks for the quick reply though!

 

[JStrateger]

I wouldn't think fuel in the cylinders would effect compression too much but to on the safe side, I would un-plug the MPI relay next time you do it though.

 

[Calan]

Leaving the plugs in the other cylinders puts extra wear on your starter and more drain on your battery. Also, you should always pull the MPI fuse (or find some other way to disable fuel flow). All that un-burned fuel flooding your cylinders for an extended time while doing the test can wash the cylinders and isn't good for your rings.

http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html

 

[phunny]

I don't think it looks like a HG problem I'd lean more towards the rings.

 

[wises4057]

i ran the numbers on his motor again today(with mpi and all plugs pulled this time). on a warm engine, the numbers(from air filter to timing belt) are 170-140-130-183....i added some oil to the middle cylinders and ran them again. they were then 170(using previous number)-183(ish)-185-183(using previous number)....so is it a good sign the rings are starting to wear? i did talk to a local mechanic here who i trust and does great work...he said he's seen these numbers before with warn valves/seals...is this possible. i dont have the tool to do a leak down test, so i cant pin point it(yet). im gonna check with a buddy whos got alot of these specialty tools cause he is a mechanic, and see if hes got a leak down tester.

if it does end up being valves/seals, how hard are they to change(hoping for my buddy's sake thats what it is haha)?

thanks for the responses guys.

 

[Calan]

Could definitely be rings, but two adjacent cylinders with low readings that are fairly close can also indicate a HG that is leaking across a fire ring. The better numbers that you saw after adding the oil wouldn't normally support that theory, but stranger things have happened.

Do a leak-down test on it to be sure.

 

[wises4057]

im hoping you are right haha i might have to see if any local auto parts stores do loaners on leak down testers. i was thinking the same thing on two cylinders a next to each other being both low. i dont see any oil or coolant disappearing, there probably wouldn't be if its just leaking between the 2 cylinders right?

thanks for the quick reply

 

[Calan]

I dont see any oil or coolant disappearing, there probably wouldn't be if its just leaking between the 2 cylinders right?

Depends on how bad it is. Usually it's just a loss in power at first, but it grows into a big problem if it blows out completely or starts mixing fluids.

There's more info on HG failures here: http://www.dsmtuners.com/forums/articles-engine-fuel/336535-do-you-have-blown-head-gasket.html

Your case does sound more like rings to me, but there's no way to be sure until you can do the LD test.

 

[wises4057]

Thanks. Yeah, he says he hasn't really noticed a loss in power, but he said there's a light stutter under moderate acceleration while boost spools up, just for a second or two, then goes away when its boosted. I don't know if that is a head gasket sign(maybe cause of the small amount of pressure escaping from one cylinder to the next?)? Other then that, I don't see any leaks, no smoke coming from the exhaust either.

 

[laserspeeddemon]

I don't think it looks like a HG problem I'd lean more towards the rings.

This. The only way to find out is to take about 1 Tbsp of oil (roughly one cap from a bottle of oil) and pour it into the bad cylinder. Allow the oil to settle for about 10 minutes and then do the compression test again on that cylinder. If the number jumps by more than 10 psi than you're piston ring on that side is BAHD!

 

[wises4057]

I should be able to do a leak down test with my compressor, just using the compression tester hose(after removing valve so air can flow in, not just out), as long as i can adjust the pressure coming through the compressor hose correct? None of the places in my town have a leak down tester in stock or as a loaner tool.

My compressor goes to about 125psi, but 40ish psi should be ok, correct?

Everything I read about doing a leak down test says to make sure all the plugs are removed, and to make sure that the cylinders are TDC when testing them. Is there anything else I would need to know before doing this for him tomorrow?

I've never done a leak down test before, so I wanna thank you guys for all your help with this so far!

 

[wises4057]

Alright guys, so I did the leak down test(twice, to make sure my results were the same twice since i hadn't done this before), but not with an actual leak down tester, since none of the auto stores in my area had one in stock. It was all 3-5 day wait periods. I did it with the compression tester hose, with the valve removed from the hose so that I could pressurize the cylinder. I ran about 40psi into each cylinder test.

I did not have any air I could hear leaking out of cylinder #4 at all(heard nothing coming from oil cap, dipstick, other cylinders, intake or exhaust).

Cylinder #3 actually had a VERY light leak coming from the oil cap.

Cylinder #2 had air leaking out cylinder #4(yes, I did test them when they were at TDC, I didn't do them in the order that I'm listing them now). That is what confuses me. Cylinder #4 had no leak, but when I tested cylinder#2(after putting at TDC) it has air coming out of the #4 cylinder. This is why I tested them all twice at TDC, because of this weird result.

Cylinder #1 had an even lighter air leak sound coming from the oil cap(had to put my ear by it to hear it).

So what do you guys think would cause the air to leak from one cylinder to another cylinder, that isn't a next to each other? I checked and double checked when I tested that cylinder to make sure it was TDC.

Thanks guys!

 

[Calan]

Please refer to the cylinders as #1, #2, #3, and #4... with #1 being on the driver's side. I can't keep up with all the references to "cylinder closest".

 

[wises4057]

sorry about that, i corrected it

oh, and my step-father(who worked on plane engines in the air force, and now retired, works on small engines) said that when air is leaking like that(from one cylinder to another opposite cylinder, it could be a good sign that the valve is burned or slightly damaged , and not seating right allowing the air to flow out the open valves on the other cylinder...does that sound right?

 

[Calan]

sorry about that, i corrected it

oh, and my step-father(who worked on plane engines in the air force, and now retired, works on small engines) said that when air is leaking like that(from one cylinder to another opposite cylinder, it could be a good sign that the valve is burned or slightly damaged , and not seating right allowing the air to flow out the open valves on the other cylinder...does that sound right?

Thanks

It's possible, but if air flows into the intake through an open intake valve, it will likely flow right on out through the intake system due to there being less resistance there than coming back through another cylinder.

How many times did you rotate the motor and test it?
Was the motor warm?
Did you follow the instructions in the article I linked to in post #5?

Since you are rotating the motor between tests, it's possible that you didn't have the valves completely closed each time. You really want to be 15-20* ATDC to make sure they are closed completely, but you need to find a good way to make sure the crank can't rotate.

You also need to use more air pressure for an audible test. Compared to combustion pressures, 40 psi is nothing. More pressure will make it easier to hear exactly where air is leaking.

 

[wises4057]

I just remembered, I hadn't opened up the throttle body plate, which would probably explain why it was coming back into that other cylinder(since it shouldn't have been able to go pass the plate). I'll have to tell him that we'll be pulling the head one way or another.