nehuge

1983 300SD, cold compression about 80. Warm compression about 200. Car only has 106k on it.

The motor shakes at idle, and nails loudly, but smooths right out at 1,200 rpm perfectly.

I switched out 3 known good injectors on that spot, and no change. (well, of course it wouldn't change as I show low compression).

Would a leakdown test show me what I got before I take the head off and look? How much for a shop to do that?

AGAIN, the craziest part is that it has all the power during normal driving, just that bucking at idle due to that compression. I'm NOT thinking this is fuel related due to the compression (but I WOULD if compression was ok).

Ideas?

Plutoe

I have no idea if this will help however compression specs(at operating temp) are as follows:

26-32bar
18bar-ware limit
3bar-cylinder to cylinder variance

I would ask the tools you used and the process you used to obtain the data. Plus no credible shop would ever think of using cold data!!

Where is the data for the remaining cylinders???

fireman1073

adjust the valves

nelbur

I am not an expert, but I understand that a leak down test can help diagnose a problem because one can listen for the leak. If the noise from the leak is coming from the oil fill hole the problem is ring related. If it is from the intake it is intake valve related, and if it comes from the exhaust it is exhaust valve related.

fireman1073

seriously...adjust the valves

they cause skipping,uneven running

carbon can build up on a valve if it is not closing fully and cause sealing problems so adjust and if problem returns adjust again after few hundred miles

pretty easy

fireman1073

also do a search on rack damper bolt

fireman1073

Nehuge did you solve this?

Glyn M Ruck

A leakdown test is the correct move. You could well have a badly sealing valve! Wet & dry compression testing will give you an idea as to whether you have bad rings on one cylinder which is unlikely.

nehuge

Sorry this took a while to get back with everyone. Did another valve adjustment, found a pinched vacuum line at the rear of valve cover from the last valve adjustment. Slightly less bucking, and slightly less smoke.

However still low compression on #3. Has all the power still, just lopey at idle (rack damper bolt new and adjusted almost all the way in, as that is the only position it has the least amount of shake).

Ideas?