Compression test with video
 

Just did a compression test and want to know what you guys think of the results.


-S4 turbo engine

-Piston compression tester

-Cold engine

-Gas pedal press down

-Both front and rear rotors show the same results but the video is of the front rotor only

-With the valve open it bounces to around 30psi each time and with the valve closed it reaches around 60-62 psi.


So yah watch the video and lmk what you guys think......


(Skip to 1:00)

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Here's another video of the car starting up the first time of the day.

2:48 start up
4:30 exhaust

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wow it runs really really well but the compression is WAYYYY to low minimum is 85psi

Yah thats the weird part i thought that if the comp. was that low it wouldn't run good but my car runs ok and idles fine. Some times the idle bounces and the car bogs/hesitate but i think thats bc of a boost/fuel leak or something.

I just got back from working on the car and found a lot of loose vacuum line, purge valve broken so that could explain why i have boost/idle problems? but one thing that concern me the most is that my mechanical OMP lever thing is loose and looks/feels broken for who knows how long.

My compression was an average of 60 psi on all rotor faces when warm and my car ran fine before I rebuilt it. Chris at RP was astonished I drove the car back and forth to work reliably every day.

As a disclaimer I am not an expert on compression tests using a normal compression tester nor on turbo models but two important issues you might want to bear in mind based on what I read.

One Turbo cars of any kind do not have as high of compression. I refer to this post.

Perhaps much more important and something you can fix is that you are never supposed to do a compression test with a cold engine as it does not mean anything. I have heard that you can make sure you are getting accurate results if you squirt about an ounce of oil into the two trailing spark plug holes I presonally use two cycle oil so it burns off better. Let the oil sit in there for a little while and start it up let it run until it is warmed up to normal operating tempature. Now perform the compression test and let us know how it goes. :nod:

~Spike~

To late to do another test bc i already strip the engine to a core and took all the harness off.

But do you think it would make that much of a difference to where my current compression will go from 60 psi to 80+ psi if i did the test with the car hot and if i add oil through the trailing hole?

How the car looks so far....

before
http://i49.photobucket.com/albums/f2...s/DSC00870.jpg
after
http://i49.photobucket.com/albums/f2...6272010005.jpg

Well you would know more about how much effort it would be to hook things back up enough to get it running. Chances are a rebuild can only help but if you do not want to spend the money I would give it a try personally. Perhaps I should ask in greater detail why you were doing the compression test. If it was just to give it a test I would probably put everything back together if it was because it lacked power or would die randomly or something along those lines I would probably just go ahead with the rebuild.

I will explain the reasoning behind doing a compression test on a warm motor though as well the oil. When you cold start a car all of the oil has drained back into the oilpan. All that seals the gap between a ring and a piston wall or a apex seal and block is a little bit of oil. What I have heard about the oil is that the injectors on top of the engine leak a little bit of fuel coaxed down by gravity. This fuel removes what ever thin bit of oil that is left over from the last time that you started the car. When you squirt a little bit of oil in the sparkplug holes you make sure you refresh the seals as well as you can without doing a full teardown and rebuild.

Again with the disclaimer I have never tried to do a compression test on a cold engine and have not tested it thoroughly enough to say with any certainty if it would make that much of a difference. Perhaps someone else here would know?

Something I would refer to is compression test instructions in the FD thread as the information is closer related to the engine you have than the N/A FC information. http://www.rotaryresurrection.com/3r...ion_check.html http://www.fd3s.net/compression_test.html I hope I have been helpful in someway...

~Spike~

Typically the compression will be lower with a warm engine than cold.

i know this thread is kinda dead but i have a question in regards to compression test with a piston compression test .. now i did one to tII that i was looking at and without holding the release buttom is was a solid 90 but when holding the realese button it doesnt give me 3 steady bounces .. so im kinda comfused i thought you are supposed to get 3 solid bounces :scratch: .. ?

heres the video of the test done ..
not holding the release button http://www.youtube.com/watch?v=Fvnd8Jeo2t8
any comments?

cant find the other vids of doing the test with the button held done .. :(

I would read through the links I posted before.

"observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range. Next let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment." -rotaryresurrection

Here is a video of what your compression test should look like for a TII:

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~Spike~

Old post, but thought I'd bring this up.


Is that not cheating? I think it is.


A while back I got 95ish on both rotors. A year later with another 4000 miles, and the motor has been sitting for a month. I cranked another batch of fogging oil through and compression tested it, and got 135psi on both rotors. Now the only other variable is the engine was warm the first time, and cold the second...

Well since a cold motor usually tests higher than a warm one and squirting oil in the chambers to artificially create sealing IS cheating, your results seem about right.

When I tested my motor, I removed the schrader valve from the tester completely, I got even pulses of 95 (front) and 90 (rear), I never bothered to reinstall the valve to get an aggregate total, as this seems pointless.