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Old 03-29-2007, 07:47 PM
coadman's Avatar
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Join Date: Feb 2007
Location: Freeport, Kansas
Posts: 226
Trials and Tribulations of my first compression test on my 240D!?

After doing much reading the past few days on how the procedure went, I ran into Wichita, Ks this morning(about 50 miles) went to Harbour Freight and purchased their diesel compression test kit(on sale of course for $17.95 or so). I also picked up a cheap mity vac as they had one there. When this craps out I will go to sears and buy a better one. My first probem occurred when I tried to take the wires off the glowplugs. The nut would turn, and so would the ring terminal on the wire. Didnt matter what I tried, I couldnt just hold the terminal. I finally let the terminal turn with the wrench, figuring I would probably break the wire. I was correct. It broke! I did find out after turning the tiny nut quite a ways, you could then back the glowplug out of the hole a bit, until you reached the limit of the initial little nut I was turning. After the wire broke, it didnt matter, I just removed the glowplug. Oh, guess I got ahead of myself a bit,, I fiddled and fiddled and couldnt get the wrench on to make much progress, so I went ahead and removed the injector lines, from the pump, to the injectors. Then I just kind of layed it back out of the way. Hooray, Progress I thought! First I tried checking the compression on the number one cylinder and got "0" reading. I messed with the fitting, and still got "0" reading. Then I remembered the instructions said to remove "ALL" the glowplugs or Injectors, whichever way you used. So, again I start on the glowplugs, Again, I had the wire terminal problem. So, this time I just clipped the wire on the remaining three, and figured I could put another wire terminal on when I was finished. I removed all glow plugs, finally Then I wondered why in the devil the little nut on the glowplug would come off so tight, while not letting the ring terminal move, so I started to remove the nut with some wrenches. Never found out why it came off so hard, as I dropped the nut on the dirt floor in my machine shed! Spent 20 minutes looking for it, and couldnt find it, so guess I will buy a new glowplug, if I cant find a suitable replacement nut in my farm storage collection. Ok, now on with the compression testing. I remembered two people on this site (right now can't remember who they were, as I read so many threads pertaining to this subject the last 48 hours, I'm goofy ) Said to cut the fuel on the motor by hooking a mityvac up to the vaccum line on the back of the IP. Wow, one thing finally went RIGHT! That worked like a charm. I started back with the number one cylinder again, cranked the motor over, and looked at the gauge, 180#. I thought, that couldnt be right, so I tried it again, while cussing at the Harbour Freight compression tester, as I knew that was the problem. Second try, same reading, 180#(or close to it) The gauge never would really hold the top pressure very long. I was very discouraged, as I knew it should be somewhere around 300. So, I went to the number two cylinder. With this one I had to use a 45 degree swivel fitting to have enough clearance to hook everthing up. Tested the number two, and had 300#, much, much better. I hooked everything up to number 3 cylinder, and again had 300#. Boy I was a crusin', really satisfied, figuring the compressor was malfunctioning on the first cylinder test. Went to the final # 4 cylinder, and ran the test a couple of times, but 280# is what it ended up at, both times, which was not too bad, considering the previous two were 300. So, I thought I would try the number one cylinder again, and use the same swivel fitting I had used on the other three, just in case something was hopefully wrong with the previous straight fitting I was using. I installed the normal fitting into the number 1 glowplug hole, then screwed the swivel fitting onto the straight fitting. But, apparantly, I had the wrench at the wrong angle, as guess what, the swivel fitting broke! so, I just used the straight fitting and proceded to test the number 1 cylinder which had been so low at the start. My hopes were high, but after turning the motor over several times, there is was 180 on the gauge! I ran that test 3 more times, but same results, 180. So, I thought, I would squirt some oil in there to see if the results were the same. Found some oil in an oil can, removed the fitting, gave a couple of squirts into the hole, re-installed fitting, hooked up compression hose, and turned the motor over. Same 0, Same 0, 180 on the scale. This recap would actually be kind of funny, if the number one cylinder would not have been so dang low. So, now, what does that tell you guys? I have not set the valves yet, this thing has been running like a scared rabbit, but it has used a little oil. How much, I cant tell you, as the odometer isnt working. I wanted to test the compression, and then set the valves,and check the compression afterwards. I need to make me a couple of wrenches with my torch and welder tomorrow, then perhaps I can get around to the valve checking on Sat or Sun. This thing smokes at startup, but after running for 15 minutes or so, when I go down the road, I dont notice it smoking much, even when I stop. I have come to the conclusion that the Harbour freight compressor is not top notch, but it was cheap, I dont know how accurate it is. I do know I need to find me another swivel fitting,and a nut for my glowplug, plus some ring terminals for the wire. Any thoughts or comments? This car really looks nice, with no dents, decent paint, just a smigin of rust on the trunk lip, and solid jack points, new tires, very nice interior, and the ac even works! So, I hate to give up on this baby! Could the number one valve be off that much, that the compression would be so low, but the car still run good?
thanks,
Jim
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1979 Mercedes 240D (Sold to a neighbor last year,now I have room for a new one,looking for a 300D this time)
1980 Mercedes 240D(bought for a parts car, but I have fun driving it!)
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