Hi folks,


I have a 98 E300 Diesel

I have low power and am looking to a compression test to see if I have good compression on all 6 cyl.

1. What PSI should it be?

2. Doing the test: remove the glow plug, screw in the tester, tap the starter and take your reading?

is it that simple?


3. If lower than what it "should be" what can I do to improve it?

thanks for any info.

Not sure on your engine. 617's run between about 330 and 400psi. It would be wise to pull a vacuum on your shut off valve while engage the starter or be willing to tolerate a running engine while doing the compression test It takes more than a tap on the starter. You need to get a number of compression strokes on the cylinder you are testing.
If you discover low compression, you'll need to figure out why before knowing what you can do to resolve it. Typically, there's not a lot to be done that doesn't cost $$$$$.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

If the engine starts OK, I wouldn't worry about compression.

If it starts don't worry about it... true...

plus.... if the compression is low you are going to need a leak down test to determine if the problem is mainly lower end.. rings, etc or upper.. valves /gasket...

So the main thing a compression test is good for is the RELATIVE pressures in the cylinders.... and which cylinders were up or down... like if two are low together.. it may mean a head gasket leak between them... there is a certain percentage psi difference between best and worst ones which the factory shop manual calls for looking at....

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Low power is not usually compession related on these diesels. I would seriously look in other places first myself.

A compression test would not hurt either but again I would not expect it to be your issue. Without many other things being examined first.

Check the archives for the common reasons for power being poor on your engine type. Many problems tend to be of a common nature.