[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: What do these compression #s mean?
Nathan Belo <firstname.lastname@example.org> wrote:
My car is burning oil. Very embarrassing for someone who props Audis as
great cars. When I start off and shift...poof! Blue cloud when I shift
and sometimes a cloud when I'm stopped at the light.
This usually indicates worn valve guides/valve seals. When you stop the
oil runs down the valves into the combustion chamber - then when you
start moving again the "poof" occurs .
1 2 3 4 5
155 125 128 143 60
2 squirts of oil in each cylinder
1 2 3 4 5
165 127 200 170 90
What the !@#$% is going on with cylinder 5?
I am equally concerned by your cylinder #3, the delta is 72psi between
the dry and the wet tests. The rings might be gone in this cylinder.
Do I need a top and bottom rebuild? Or do I have a bad valve at 5?
Ring job? Is it better to just buy an engine from a junk yard and drop
it in or rebuild? Say it's just a bad valve!!
It might be the valve in #5. Still you need to conduct a leak-down test
which is far more accurate.
Pump up the pressure in each cyl one by one, at TDC. Observe the reading
on the gauge. Listen to where the hissing comes from. Make sure you
remove the oil filler cap, coolant expansion tank cap and the intake
rubber boot beforehand.
-if from the IM, it's the intake valves.
-if from the tailpipe, it's the exhaust valves.
-if from the valve cover oil filler hole, it's the rings (through the
crankcase ventilation sys).
-if bubbles appear in the coolant expansion tank, the head gasket is
shot between the oil and water jackets.
Re: rebuild vs. replacement your engine with a used one.
I personally like to rebuild my own components coz I know them and I
trust them. I've done several head rebuilds and 2 bottom ends, no big
deal, just time consuming.
OTOH, your engine has 173kmi on it. In your case I'd probably find a
wrecked low mileage 200 and drop an MC or better yet a 3B in your 90Q.
Hell, the front end of your car should be identical to a CQ so you
probably could build a 4-door S2 out of it.
Talk to Brandon Hull, he's in the process of building an S2 as we speak
and has all the p/n on hand.
'89 200TQ -- 18psi (TAP)
'98 A4TQ -- nothing to declare