Hi, I am going to perform a cylinder compression test on my 1994 audi 90s. Its blowing blue smoke when it gets warm and I want to see if the rings or valves are bad. The car has 148k miles on it, I have kept it in excellent condition, but things happen to an old car... Does anyone have a manual for this year car that lists the standard compression reading for the cylinders? I supposed I need to look at if one cylinder is off but wanted to know what the standard is so I can figure out how worm the engine is.

If anyone has any tips on performing this test I would appreciate the input.

The steps i am following for the test:
1. let the engine get warm
2. remove the spark plugs
3. remove the coil wire
4. attach the cyl comp. gauge.
5. open the throttle
6. crank the engine once
7. check the gauge after the first crank, note the number on the gauge
8. crank the engine three more times until the highest number is reached, note the number on the gauge
9. reset the gauge
10. repeat steps 4-9 for remaining cylinders

If one cylinder reading on is lower then the others, drop a bit of oil in the cylinder and retest. If the psi goes up 10-15 then the rings are bad. if no change then the valves are bad.

 

Compression test might not tell you much as was the case with my 4000S. I had good compression in the 150psi range across all cylinders but it was burning oil faster than gasoline. After I took the engine apart I noticed that the oil scraper rings were flush with the pistons. New rings solved that oil burning problem.

6. crank the engine once This might not give you a good reading since controlling a single turn is going to be difficult and will give you a low and unbalanced readings. You want to measure the maximum that your engine can generate and for that you will need to crank the engine for at least 5-10 sec per cylinder or 4 to 5 revs.

 

here is the procediur.

1. heat the engine till 90C.
2. remove the spark plugs
3. put in the metter
4. crank the engine till the guagg doesnt really change values.
5. do all cylinders
6. recheck the first
7. put the plugs in
8. retighten after engine cooled.

You can use a teaspoon of oil, to get the maximum. but if you really want too.
always in regular use, firts rings that go is the oil scrapers, or number 3. Why couse they scrape oil and sooned or later colect enough scum that they stick inside. Nothink can be done about that. after they stick oil gets into combustion engine and burn, leaving ash on the sides of combustion chamber. then ring 1 goes becouse its the first to clean the ash. then a while 2 goes. and no compresion.
basically if compresion falls below 6bars, there is almost no way to start the car.

if you use hand held guagg, use your body weight to keep it, couse there is a lot of preasure that will shot it out if not held properly.

BEST way to get the compresion back is to re ring the engine, or sometimes rebore it if access body wall is eaten. up to 0.15mm I think.

 

Here are the test results.

Cylinder 1 = 208
Cylinder 2 = 208
Cylinder 3 = 170(3rd try); 1st try = 150, 2nd try= 160
Cylinder 4 = 208
Cylinder 5 = 185(2nd try); 1st try = 160
Cylinder 6 = 208

After the test above I then added a little oil to cylinders 3 and 5 and retest

Oil check Results:
Cylinder 1 = 208
Cylinder 2 = 208
Cylinder 3 = 208
Cylinder 4 = 208
Cylinder 5 = 250+
Cylinder 6 = 208
- 5 went to 208. Means that the rings are bad...maybe someone can comment here???????????
- 3 went off the chart...maybe added to much oil...maybe someone can comment here too???????????

One fault though - I may not of had a WOT for the entire test (realized it after clean-up drr!...)maybe someone can comment here too???????????

sorry for the eye-catching ????'s

james

 

Hey man, the oil scrapers. Yes, yes indeed...How long can I go like that, or how will I know it's getting worse? Whats the rate on that? She's a good car.

 

Here's the cylinder pattern.

3 6
2 5
1 4