1983 OM617 300SD...knocking on cylinder #3. I took known good injectors and put them in its place no change. The car acts JUST like this one in the video...when you rev it up to about 1,000 it it smooths right out, no knock or shake.

https://www.youtube.com/watch?v=rAOVL3C0dvg

I did a diesel purge for 1/2 hour and new filters..Still no change.

Is this a prechamber issue? An injection pump not telling that injector what to do correctly? Or is this simply a valve adjustment needed?

It had a valve adjustment about 3,000 miles ago and I heard sometimes you need to do it twice in a short time span.

Ideas?

How do you know it is #3?

I'd try a valve adjustment first (easy / cheap), and then if you've got some spare heat shields, move #3 injector to see if the problem follows.

After that I'd try rebuilding the #3 delivery valve (replace the copper washer). Be very careful here, make sure you're confident that you have the right info and proper tools, as you can throw the pump out of adjustment or damage it if you do the wrong thing.

If the problem still exists, remove #3 injector again and re-position the hard line so you can spray that injector into a glass jar or metal can and observe the spray pattern, do the same with #1, and compare to see if your injection pump is bad. Very doubtful but possible especially if someone has "adjusted" or "repaired" your injection pump.

After that, I think it's time for a compression test AND a leak-down test.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

I know its #3 since when I cracked open that particular line the tapping stopped. The tapping also stops over 1000 rpm like in the youtube video I attached.

I never thought about spraying them into a jar, I just figured you have to pressure test them (have to have the equipment or take it somewhere).

I'll look into and check back.

There is a chance the calibration of the third cylinder element in the injection pump is off a little. This can be proven and the situation improved using the milli volt method.

Basically the method is to measure the voltages at the glow plug harness to engine ground with a meter. If an element is advanced the voltage at that cylinder will be higher.

To make sure the test is done properly you have to take in the condition of the glow plugs as standards. Most times this may mean buying a couple of new ones for testing purposes. You have eliminated the injector basically already.

Did valve adjustment, 3 out of 5 were too tight. Still have the knock however.
I still need to try the "jar" method sometime and check back with you guys. Perhaps even the delivery valve copper.

Did compression test tonight, most cylinders are 360, and #3 is 170. What gives? Again, after 1,000 rpm its got all the power and smoothness.

If #3 is 170 psi after a few proper, consecutive valve adjustments, that cylinder has an internal defect. Usually, if it has been a long time since a valve adjustment was last done we suggest doing the job and then doing it again after ~500 miles or so. The idea is that after so long, Carbon builds up around the tight valve's loose margins and the first adjustment causes it to be broken away. That leaves the valve margin loose again, so the second adjust sets it for real.

Something's broke. We can't know what unless you do some digging.

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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it!
'85 190D 2.2 Auto *Cali* (Blue/Blue) *sold*
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Would a leakdown test help narrow down what it is before I pull the head?

Yes, but no matter what it is it'll require some deep surgery. A leakdown might let you know if it's something you're willing to fix or not. It's not hard to do, so go for it and let us know what you find so we can speculate.

__________________
'84 190D 2.2 5MT (Red/Palomino) Current car. Love it!
'85 190D 2.2 Auto *Cali* (Blue/Blue) *sold*
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I'll do that in the next couple weeks and report back.

Awesome.

__________________
'84 190D 2.2 5MT (Red/Palomino) Current car. Love it!
'85 190D 2.2 Auto *Cali* (Blue/Blue) *sold*
http://badges.fuelly.com/images/sig-us/302601.png
http://i959.photobucket.com/albums/a...0/sideview.png

I did Marvel Mystery oil in that cylinder for a week and no real improvement. There isn't lots of smoke, and the power is perfect over 1,100 rpm and no misses at all. Leakdown test time ?