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  #1  
Old 05-24-2003, 05:12 PM
slowlane
 
Join Date: Aug 2002
Posts: 198
Factory Compression Numbers

I do not have the cylinder compression spec. for my 92-400E-119975 engine, anybody have them? would like to know if my numbers are in spec with my engine milage of 96,000.

I just check my engine compression and I came up with these numbers, does anybody else have their 400E numbers?
Thanks to those who keep it possible for all Americans to enjoy their drive this Memorial, timreid

5 172 12kg
6 171 12kg
7 170 11.9kg
8 174 12.3kg

1 180 12.7kg
2 182 12.8kg
3 176 12.4kg
4 175 12.4kg
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timreid
1992 400E
euro lights
500E sway bars
210 16in wheels
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  #2  
Old 05-24-2003, 06:51 PM
Registered User
 
Join Date: Oct 2002
Location: Portsmouth UK
Posts: 170
Hi

Sorry I not have the specific information you requested.

However, from first principles your results indicate that you do not have a problem with a compression ratio just shy of 12:1 and insignificant scatter.
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NormanB
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K
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  #3  
Old 05-24-2003, 07:06 PM
slowlane
 
Join Date: Aug 2002
Posts: 198
Thanks
NormanB, "you do not have a problem with a compression ratio"
Very glad that you indicated no problem, the engine just feels as if there is a loss of power. Wonder if it could be in the fuel delivery system?
enjoy your drive, timreid
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timreid
1992 400E
euro lights
500E sway bars
210 16in wheels
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  #4  
Old 05-24-2003, 07:13 PM
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Join Date: Oct 2002
Location: Portsmouth UK
Posts: 170
Tim
This is a tuff nut.
Best option is to get it on a dyno and see what she is actually pulling - but if you have had the vehicle a while then your intuition is probably correct and power is down.

Cause well you are right it could be fuel even something stoopid like a fuel filter - do the easy obvious stuff and if no joy ensues get it to a reliable indy and get it gauged up.
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NormanB
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K
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  #5  
Old 05-24-2003, 10:04 PM
slowlane
 
Join Date: Aug 2002
Posts: 198
NormanB, I notice a few months ago that the spark plugs were indicating a rich fuel mixture and at that time I felt then the loss of power. So I decided to have the dealer shop to check out the fuel system, and the O2 sensor was not functioning correctly, so they changed it out. But I still felt there was a loss of power, so I decided to check the compression.
After your first reply, I went out and check the spark plugs I just pulled (about 1000 usage) and again they indicate a rich fuel mixture. I have little knowledge of fuel system (HFM-SFI), and I have no idea why the plugs are carbon fouling? A friend named Ludwig from Germany told me to try the Bosch F9dc0 plug; Iím using Bosch F8dc4 that the owner manual indicates to use, but it also calls for F9dc0. Ludwig said MB went to the F8dc4 to improve the idle, however itís a colder plug and may indicate a rich fuel system and the f9dc0 will burn the fuel better. I do remember my original plugs were f9dcoís. However the f9dc0 plugs are not available in the US, so Ludwig got the f9dc0 from Germany. I installed the f9dc0 today, and maybe it will correct both problems ??
I changed the fuel filter at 81,000m, I have 96,000m, but as you suggested start with the obvious things, so Iíll try the filter change after I driven with these new plugs for a 1000m.
Thanks, enjoy your drive, timreid
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1992 400E
euro lights
500E sway bars
210 16in wheels
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  #6  
Old 05-24-2003, 11:28 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,036
The ratio of atmospheric pressure to cranking compression pressure is not a computation of compression ratio i.e. 180/14.7 = 12.24. As air is compressed it heats up so there is not a linear relationship between volume ratio and pressure ratio.

Guys fret endlessly about compression readings - too high, too low, whatever. Actual cranking compression pressure is a complex interaction of compression ratio, valve timing, and cranking speed. Absolute numbers don't mean that much. The thing to look for is consistency across all cylinders.

The twelve pound variation between your high and low readings are "okay", indicating the engine is probably in "good" mechanical condition, not "great" not "fresh" - the old gal has some miles on her, but with good maintenance and good driving habits, she's probably got plenty more.

Take more readings in the not too distant future and see how they compare. The average over the counter compression gage is not a laboratory precision instrument, and you might be surprised how much the readings may be change at another point in time.

Compression tests should be done with the engine at operating temperature, the throttle blocked open with the ignition and fuel system disabled, and sufficient compression strokes should be run - generally about five if not six, for the gage to achieve a peak reading. Then this should be repeated two more times for each cylinder to verify consistent readings.

Duke
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  #7  
Old 05-24-2003, 11:39 PM
slowlane
 
Join Date: Aug 2002
Posts: 198
Duke you know what I forgot to tell my helping hand (wife) was to press the gas pedal to the floor, oh my, oh well. What effect does this have on my compression test?
timreid
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1992 400E
euro lights
500E sway bars
210 16in wheels
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  #8  
Old 05-25-2003, 12:24 AM
zeronero's Avatar
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Join Date: May 2003
Location: San Francisco Bay Area
Posts: 426
I don't know if you still need compression test numbers but I had mine done at 120,000 miles and it was at 180psi for every cylinder. I the engine feels slugish I might think it could be the transmission. Not a problem with it, just how the ratios are, very tall gears. This car can go over 130mph in 3rd
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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500
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  #9  
Old 05-25-2003, 12:33 AM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,036
Quote:
Originally posted by timreid
Duke you know what I forgot to tell my helping hand (wife) was to press the gas pedal to the floor, oh my, oh well. What effect does this have on my compression test?
timreid
Welllllll... it might make the cylinder to cylinder readings a little more inconsistent than they would be with the throttle wide open so there is no restriction to air flow.

I think not blocking the throttle open for a compression test is a common error.

Duke
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  #10  
Old 05-25-2003, 07:47 PM
slowlane
 
Join Date: Aug 2002
Posts: 198
Duke thanks for your very good and detailed explanation about compression. We know there are many reasons for low compression as (leaking valves, deposits, worn rings,head gasket, etc.)
And from your explanation of compression, there are various factors that influence these numbers at the time of testing, but when are compression numbers considered on the low or even the high side. My total average is 174 or 12.3 and as you said all the cylinders are fairly equal, but the girl has been driven?
I cannot find the MB's recomended compression numbers, does anybody have these numbers?
Thanks timreid
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1992 400E
euro lights
500E sway bars
210 16in wheels
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