compression test noise!

[packinkimber45]

Hello everyone, I was wondering as far as compression tests go. Do you just keep cranking the motor until the needle stops moving up? I've heard yes and no. Can someone clarify this for me. Also when I did a compression test tonight I heard a pop noise in what sounded like the cylinder. It just popped once, like a snapple bottle cap inside an enclosure. Did I screw something up or is this something I should be concerned about? When I did the test, the car was fully warmed up, disconnected mpi fuse, wot, but I did not disconnect coil plug or any spark plug wires off of coils, spark plugs where laying on top of intake mani. Please tell me this is normal or it's something the compression gauge is suppose to do if you crank it too much. I had it cranked a little too much just right after needle stopped on the compression gauge. I need fast answers please, I have to go to work in the morning and I am scared to drive the car. My results were 155 all the way across, and these numbers were the results from cranking until the needle would not move anymore. Thanks.

 

[DJYoshaBYD]

155 is kinda low... I think the service limit is 160, but I dont have my book in front of me...

 

[packinkimber45]

I thought that number was good. I am really concerned about that noise though. Anyone know what it was and if it is something I should be concerned about? Thanks.

 

[JohnCIV_Talon]

155 is just fine, as far as the popping noise goes, I cant help you.

 

[packinkimber45]

Ok thanks. That really worries me, I have to go to work and I am scared to drive it. Anyone else? Any moderators that can tell me what that noise was and if I should not drive the car? Thanks.

 

[romeen]

I know what you are talking about when you talk about the popping sound. I really don't know what causes it but I can tell you that both times that I have done a compression test on my motor it made the same sound regardless of which cylinder I had the tester hooked up to. I was by myself so I really can't tell you what things looked like under the hood when it happened. However I can tell you that my compression is fine across the board and my car runs great. Hopefully that is a little reassuring. I would like to know what causes it as well.

 

[packinkimber45]

That popping sound you heard on your car, is it like a repetitive popping sound? Or is it just a single pop? That worries me, because on my other car (94 gs) I did a compression test on it last summer and I stopped after hearing that noise. Just a couple of months ago, that same cylinder I heard the noise on when I pulled the plug, the electrode was gone and part of the porceline was broken off and now it runs like crap, like motor got screw up. I definately dont want the same thing to happen to my tsi or even worse. Thanks for sharing that though, it makes me feel a little better. I too would like to know what causes it and if it something to be worried about.

Anyone else that can tell us this noise, what it is, what causes it, and is it something to be cautious about? Should I not drive my car to work. Thanks.

 

[romeen]

It's a single pop. Your initial description was pretty good. It similar to when you open the cap of a vacuum sealed container and there is that initial pop. I thought maybe air was suddenly escaping past my guage since it happens towards the end of a cranking cycle. But I'm still not sure. Like I said, my compression although a little on the high side is very consistent across all cylinders and my car runs good and pulls hard.

Also, I have had my plugs out several times since then and they look fine. FWIW, the piston tops as much as I can see by shining a light down the plug wells also look fine.

 

[dsm-onster]

Perhaps that's what it sounds like when air is escaping from around the seal of your fitting at the spark plug oriface. It happens w/ me if I don't get the fitting on tight enough. It's hard to do that as your hole is way down in the head (that sounds dirty ).

 

[4g63t]

I herd the same noise twice tonight but my car runs the same. I wonder what it can be.

 

[romeen]

I finally figured out what the noise was, at least in my case. When the guage and more specifically the vacuum hose that is attached to it suddenly filled with air when I was cranking the motor it caused the hose and the guage at the end to kind of jump up (for lack of a better description). When the guage was falling back and hitting the valve cover it was making that sound. I can't say for certain that this is what is going on for you other guys but try having someone crank the motor while you watch the guage and see if it is doing the same thing and let us know.

 

[Talesin]

155 is fine, and normal for a turbo 1G. 160 is factory new spec IIRC for the lower-compression turbo 1G pistons. I believe the service limit is around 120... given that all four are pretty much the same, seems like the engine is in good working order. Got some BS from a mechanic who said that 150 was needed for proper combustion, but my first engine tested out at 135 across the board and ran perfect, until my mechanic-at-the-time accidentally nicked into the heater core feed hose, causing it to burst on the freeway and warp the head after all the coolant dropped.

2Gs will read higher, due to their stock higher compression pistons (more conservative timing maps compensate for it).
And I wouldn't worry too much about the popping noise, so long as compression came back good and the needle still went up on subsequent piston strokes. Generally three to four needle jumps are the standard procedure, but you can keep cranking until compression levels out and won't go up any more... usually gets to a plateau point that's pretty reliable, pretty quick.

 

[motomattxxx]

The popping is the gauge fitting seating, and its normal.