Compression Check DIY for a 1.8T

You'll need: Flat head screwdriver, 3/8" ratchet with 6" extension, 5mm Hex drive or allen wrench, 5/8"spark plug socket, compression check gage with hose, and about 30 minutes.

1. On a warm engine, open the hood andlocate the 3 plasticfasteners on the enginecover.

2. Using a largeflat head screwdriver, turn the fasteners counter clockwise. They should pop up. They do not come out all theway,so don'ttry topull them out completely.Then remove the plastic engine cover.



3. Using a 5mmhex drive or allenwrench, remove the8 socket head cap screwsholding in the ignition coils. Place these to the side,so the don't end up falling into one of your cylinders later.



4. Gently pull the ignition coils out,and your spark plugs will bevisible.

5 Using a standard 5/8" spark plug socket, remove the spark plugs. Now would be a great time to check your plugsto see if they need to be replaced. Also, (optionally) you can disconnect the electrical connectors to the fuel injectors, so that yourinjectors don'tsprayduring the compression check.



6.Connectyour compression gagein the first cylinder,turningthehose until the o-ring makes a good seal and is tight.

7. Crank the engine over,about 8-10 turns isplenty.The engine will turn over quietly and with much less effort since there are no spark plugs in the other cylinders. CAUTION: DO NOTATTEMPT TO CRANK THE ENGINEBEFOREREMOVING THE COILPACKSFROM THE OTHER CYLINDERS - YOU DON'T WANT TO ACTUALLY START THE ENGINE.

8.Check your compression gage.The needle should remainat the highest PSI levelachieved in that cylinder.If it seems toolow, check to make sure that it isconnected tightly enough for theo-ring to seal properly.Hit the release valve on the gage and crank the engine again to double check the compression, if you're having doubts. Write down the PSI.



9. Repeat this for the other 3 cylinders, and you now know the compression of all your cylinders.

10. Put your old plugs back in (or new ones) and put the coil packs back on (torque 5mm socket head cap screw to 7 ft-lbs - if you're the kind of person that needs a tq wrench for everything). It is also a good time to wipe out any dirt or crud that might have built up around or under your oil cap. Put the plastic engine cover back on, and you're done.

The service tech at my local dealer told me the compression should be about 180 psi for at 1.8T or 2.0T, and 160 psi for a 2.8 or 3.0 (normally aspirated). Cylinders should all be within 10% of each other. Ideally, thecloser they are in range, and the higher the compression, the better.
A fresh 1.8T engine should be atabout 200 psi, and lower than 140 psiis considered the lower extreme. Anything less thanthat, and you might want to consider checking into why it isreading low.


Trouble Shooting
If it reads low - firstmake sure your gage is reading accurately.

1. Make sure you read the compression while the engine is still warm. It needs to heat up to get to maximum compression. If the last of the cyclinders you check are lower than the first, it could also be because the oil is leaking by the piston rings from cranking the engine.

2. If it still reads low, put a little motor oil (5w30 synthetic or whatever you use) into the cylinder through the spark plug hole. This will help make a betterseal between the cylinder walls and the piston rings. If the compression now increases, it is a sign that the cylinder walls/piston rings are worn, and you're due for some cylinder honing and new rings.

3.If the compression still reads lowwith a little oil added into the top of the cylinder, itcould besign that air is leaking from the combustion chamberthrough the valves.Try some trusty valve / injector cleaner in your tank, or ifit's really bad,you mightbe in for somehead work.

Please check your engine specifications foryour acceptable compression ranges, and usethis only as a guideline for general information.

 

What should the readings be? Is there a certain number they should be at?

Josh

 

i assume it's the same procedure for the 2.8? i was trying to do this b4 too but couldn't figure it out lol. so u do it with all the plugs out first right?

 

Edit this with what the correct PSI should be for the different engines and itll make for a good DIY thread in the DIY section.

 

DIY is edited with (normal) PSI measurements from the dealership.

 

yes, same procedure. and you can do it with the plugs in. just make sure to god that the coilpaks are not on the plugs...

best to take all plugs out as it make it easier to do them all at once and you won't foget anything

 

you should unhook the injectors so you dont have a pool of gas in the engine. Also, a fresh engine should be at 200psi across the board. The min is like 140psi and you shouldnt have more than 10% difference between the highest and lowest cylinders. If you have either less than 140psi or a larger difference in cylinders, you really should consider trading/selling (hard on the conscience i know) the car or rebuilding the engine by having the cylinders rehoned and adding in new rings.

 

Good call Cincy, it may be a good idea to take out the injectors, especially if they are bigger than stock injectors.
Might be a better idea to pull the fuel pump fuse, so there is no fresh fuel getting pumped in (never tried this either yet). Plusyou don't risk unnecessarily damaging the injectors/o-rings if they are old and you're not careful. This could cost someone much more than they thought they were getting into, and it will addsome time to the process.I've never pulled out injectors just for a compression check, have you, seriously?
Cincy, I'll edit the DIY to add 200 psi for a fresh engine, and 140 for low range.
I was thinking of adding a trouble-shoot too, if reading low compression.
Add a bit of oil to the cylinders through the spark plug holes (to make a better seal between the piston rings and cylinder walls), and re-check the compression.
If the compression increases, it's a sign of worn piston rings/cylinders. If the compression does not increase, it's a signairmight beescaping through the valves. Is there any injector/valve cleaner recommendedespecially for audis. I have used Techron in the past.
Any additional thoughts or comments? Thanks.

 

everything sounds good, but you can just unplug the injectors electronically, you dont have to remove them

 

plus you don't have to play guess and test to find the fuel pump fuse if you don't have a manual.
do you happen to know the min/max compression for the 6 cylinders 2.8 and 3.0? the dealer said avg = 160 psi.
also, the 2.7 twin turbo compression? i didn't even ask about this one.