i posted several months ago about my shakin' diesel problem on my '84 300d turbo. i adjusted and replaced the rack dampener endlessly but never found resolution. i kind of gave up and the car has been sitting for a few months now. i finally got the courage to take in into the shop to find out what the deal was. the first thing they wanted to do was a compression test. they said the compression range for each cylinder on my car is 300-400. one of the cylinders is at 180. he said that is what is making it shake. keep in mind, it only shakes when the engine is hot and only at idle speeds. there has been no loss in power and no oil leaks. they basically gave me the option of an engine overhaul which is probably not worth the cost. does this sound like the only solution? would a compression issue cause a relatively minor problem such as this?

Okay, does the shaking go away when in gear? Or Does it only happen under load/in gear? I had the same problem, a rak damper pin (I think this is what it was called) fixed the problem. It only happened when hot, at idle, in gear. Hope this helps...

it only happens when hot and at idle. i dont know about the in gear thing....its an automatic. i've adjusted and replaced the rack dampener to no avail.

First and foremost, are the valves adjusted properly. If not, that would surely give you a low reading in a cylinder. Then I would try using some Lubro Moly Diesel Purge to clean out the injectors. Then try a bottle of Redline Diesel Fuel Catalyst in one tank full.

Is the injection pump properly timed? Check that.

How are the engine mounts? If any of the mounts are broken, it will surely feel like a very rough running engine.

Try the least expensive things first.

If that doesn't work then go on to the following:

I would get a second opinion first before doing major engine work like this. If it truly is a low compression reading in one cylinder, I would want to know if it were the cylinder head valves or the piston rings that were leaking. The way this is done is to pressurize the "suspect" cylinder with compressed air at TDC and listen where the air is coming from. If your hear hissing air coming from the tail pipe, then the exhaust valve is worn. If you hear hissing air from the intake (you'll have to remove the cover from the air intake), then the intake valve is worn. If you hear hissing air from the oil cap (you'll have to remove the oil cap), then the rings on the piston are worn.

If it was the cylinder head valves, then all that needs to be done is to remove the cylinder head for overhaul, not the whole engine depending since you didn't mention mileage in your post.

The worn rings are the worst case scenario because then the engine would indeed need overhaul, not just the head.

I hope this helps.

Herb
'82 240D

I agree with the diagnosis. If one cylinder is 180, it would definitely make it shake. I would expect that they checked valve adjustment in the offending cylinder. If the valve adjustment on that cylinder was not checked, they were not adequately thorough. Once you know the valves are properly adjusted on that cylinder, you have almost complete data. The next thing to do, and what they should have done at the time is to squirt oil in the offending cylinder and check compression again. If with the oil in the cylinder, the compression comes up appreciably, the problem is cylinder related, if not the problem is valve related.

Another good test would be to use compressed air for a leakdown test. While the compressed air is applied to the cylinder, if you here the air escaping through the oil filler hole it is cylinder bore related, if it is through the exhaust or intake, it is valve related.

Best of luck,

Hey sco,

please consider about delivery valve copper washers which may produce stalling-shaking during the idling period.

Mostly people does not care about those washers but they help to keep high pressure between pump and nozzles and should renew periodicaly however corrosion and any crack can cause the leak amount of high pressurized fuel and that cylinder become late to open of nozzle pin in due time.

Here is the easy check to discover which cylinder can cause the shaking,

just bleed (loose by 17 mm wrench)each injector pipe and that is the failed one if shaking character(sound)does not changed.

Hope those are help your shaky MB!!

Good luck

Cuneyt Tekin
Lucas & Bosch Fuel Inj.Mech.

Sco B,

Larry Bible's method of squirting oil and taking a compression reading is easier than my method of applying compressed air to determine if the valves or the cylinder are worn.

You would have needed to have access to an air compressor for my method which might be a hassle for you.

Go with what Larry said.

Herb
'82 240D

jazzbo offers good information regarding checking for the bad cylinder by individually cracking open the injection delivery fittings. However, you already know which cylinder is the culprit because of the compression test.

Also when using jazzbo's method of locating a weak cylinder, don't expect the bad cylinder to have NO change when cracking open the fitting, it will just have LESS effect than the other five.

Good luck,

sco

Please, please, please, DO NOT add oil to a diesel cylnder and then test compression!!!!! There is a very good chance the cylinder will fire on the oil, or that there will not be enough space in the head for the oil -- one will blow up the compression guage unless it is certifed to 1500 psi or more, and the other will surely bend a rod or three. Do the leak test instead. Save the oil trick for gasoline motors!

Peter