Compression test on my 240D? - PeachParts Mercedes-Benz Forum

coadman · #1 03-29-2007, 04:04 PM

Done some reading on here for the past few evenings, but I want to clear up some questions I have before I proceed. I purchased one of the diesel compressor testors from Harbor Freight(mostly because it was cheap, on sale, and available when I went to Wichita today).The adaptors they have in the kit for Mercedes list models 190E 2.5L(1988-1989, E300 (1991-1999), and E320 CDI(2005). The older models have 12x1.25 thread listed by thier names, the newer one has 10x1.00 listed by it. I've never had the glowplugs out on this, although the po had just recently replaced them(they should come out easy). Do I use the adapters with the 12 x 1.25 thread? What do I unhook so as to keep the car from starting? I've read when some people are using the tester in the injector holes, they unhook the injector line(somewhere?). I think I also read where someone wired the stop button to close. I can push my stop button all the way against the stop, and the motor doesnt die. What do you suggest? I would like to do this here within the next hour or so, if you have any advice, please fill free to let it flow!

In the manual that came with this, it says to take out all the glow plugs, and install the testor in the first , FULLY depress the fuel pedal,and crank the engine for 8 revolutions. Record the reading on the tester. Release the pressure and move to next. I thought I read on here where you take two readings, one iniatially(I dont know how many engine revolutions?) then one later for maximum pressure. How does a person do that?
thanks,
Jim

GRIESL · #2 03-29-2007, 06:21 PM

When I used the HF kit, I used the injector hole. If you're shutoff isn't working, I'd remove the injector lines so no fuel gets in there. I don't think your model requires opening the throttle--mine didn't. Make sure the motor's warm. I would consider doing a "dry" test first, then squirt a teaspoon of oil in the injector hole and redo the test. That helps to determine if you've got bottom or top end compression loss.

bgkast · #3 03-30-2007, 03:44 PM

I used the injector hole too. Be sure to remove all of the other injectors to get a better cranking speed and eliminate any chance of the car starting.

toomany MBZ · #4 03-31-2007, 03:08 PM

I used injector holes as well, they all need to be removed to give an accurate reading. GP holes will work, take 'em all out. With your third hand, keep shut off lever down. Cannot think of why someone mentioned to open fuel, you want just opposite, so it won't start. Around eight cranks will be sufficient to give you a reading, whenever it stops raising compression, just to be sure.

coadman · #5 03-31-2007, 04:42 PM

I had a HF compression testor and it had the fittings for the glow plug holes. Removed all the glowplugs, used a mityvac to add vacuum to shutoff fuel line(which worked great!) tne checked the compression. 150,300,300,280. I checked the #1 several times, and still had same low reading. Someone suggested setting the valves, and seeing if the number one increase. I set all the valves, everyone was too tight, and rechecked the number one cylinder. It raised it up to 290. I checked the #4 cylinder and it was 310. I couldnt check the two in the middle as I broke the little swivel fitting that I need to check them. Replaced all belts and hose, just got done about 15 minutes ago. Took it for a test spin, I can't say it runs any better than it did, maybe a tad bit "doggier", but maybe the valve adjustment needs to get sitted in? I do notice that I have a couple of injectors leaking, that were not leaking before. Is this typical after a valve adjustment? I order some new fuel line hose to change the ones out on the injectors, when they get in. I had quite a story leading up and through my first valve checking, it is in my other thread.
Jim