CTD compression test

lomodyj

lomodyj

Well-Known Member
Joined
Mar 21, 2005
Location
Out in the Middle
Nothing in the FSM on how to perform a compression test on the CTD. I'm going out in a little while to pick up a tester for diesels (thnks blkvoodo).

Should I do the test with the cylinders "wet"?
Have all the injectors out or just the one that I'm testing?
3-4 engine revolutions?
 
we test mercedes all the time with all injectors out or one at a time, I haven't seen that it makes that much difference. Yes, several revolutions of the motor. When you say testing "wet"...you lost me. Unless it's been sitting around with the injectors/intake or exhaust off of it, then the rings/cylinders should have a coating of oil still on them. With the problem you are having, if it is in fact a compression issue, you should have no trouble pin pointing which cylinder as it will be grossly low in comparison to the others. I have a diesel compression tester that you could borrow, I don't have the adaptor for a cummins injector though.
 
Thanks Greg. I found this on the TDR:

1. Remove all injectors
2. Install adapter
3. crank engine over with starter until guage stops climbing
4. Record results
5. repeat 5 more times
Click to expand...

It was later ammended to say go with the readings for the 3rd or 4th revolution.

By "wet" I was thinking like doing a gasser motor. Dribble oil down in the cylinder to help "seal" it. Found that this is not a good idea on diesels, especially CTD's. What tends to happen is the oil collects in the piston bowl and does no good for the rings...and it can ignite...kinda fawkin' up your friends compression tester...
 
you do a wet test to help identify the compresion problem after you do a compression test. Otherwise for example if you had poor rings in a cylinder you could mask the problem by doing a wet test. Dry run will tell you where the problem is, wet or really a leak test will tell what the problem is.
 
Just pulled the compression:
From front of engine
1. 500
2. 480
3. 490
4. 490
5. 510
6. 490

I think ive got a good block/head...whoohoo!

Now for the injectors.
 
I'd bet a bad pump and/or injectors due to crappy grease or watery grease(why I got away from straight WVO). If you have to give it throttle to get it to start chances are a bad pump, if that's the case you need to call this guy...616-260-1396 diesel performance. He'll pretty much build you a pump however you want it, he built us one for a 12v that has close to 3 times the flow rate of the stock pump,it's overkill but that's what he wanted.
 
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