I just did a compression test today and was wondering whatz the 'spec' compression psi on the 1996 C280 (m104) engine

here are the readings

cyclinder 1 110 psi
2 110 psi
3 105 psi
4 100 psi
5 95 psi
6 105 psi


thanks

Did you have the throttle plate open when doing the test? You'd be hard pressed to keep up with a bicycle if those are really your numbers.

Sixto
95 S420
87 300SDL

Numbers should be closer to 150 psi. I think sixto hit the nail with the hammer.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

does the plate needs to be open??

Oops ok i need to redo it

On a six throttle Porsche opening the throttle will really matter to compression numbers. To a 104 motor with a manifold the size of a bathtub, I doubt it will make much difference.

Those numbers tell me you have a problem with your gauge or technique. They also tell me your engine is fine.

Of course the other posibility is you have a cam timing problem and the numbers are real. Basically the numbers are even and that what a compression test looks for. To make quantitative analysis from compression numbers you need to know your gauge and the engine involved more than is available here.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

yeah i might have a cam timing problem after i installed the RENNTECH cams on it

i have re-done the test today with the throttle plates open and the numbers are a little higher

1-105psi
2-100psi
3-120psi
4-120psi
5-100psi
6-120psi

So what do you think Steve? does the numbers looks OK? and how much diff could the cam timing makes?

the guage that i use is a new guage, with a PVC hose..

so what you are saying is that as long as the pressure variation between each cyclinder is not too diff, then i should be ok (in terms of doing a compression test.) then what other ways i can use to determin if my engine is losing compression??

the engine got about 180k miles on it.

Thanks

You have even numbers (sort of, you are pushing the 10% rule). This says a lot, but it misses a lot. It depends what you are trying to answer.

If you are looking for a single cylinder misfire, compression isn't the problem. If you are looking for a general performance problem, you need more info. For me I never accept a low compression reading til I have seen a normal one (that day, that gauge). If I place the gauge on the car in the next stall and I get 180 straight across, I know there is some across the board problem. Cam timing comes to mind.

If you are down due to cam timing you need to fix it. The engine will overheat and the poor combustion will coke up everything with carbon, over time.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician