126 /617 Engine shake at idle- Rack damper already done

Ok I am getting engine shake and it started about 4-5 months ago.
* When I start the car cold I do not get it.
* I can drive around in the city and it seems to never do it.
* If I drive on the highway and then exit after 5 or more minutes of sustained highway speeds (roughly)it does it and sometimes will not stop even after driving at city speeds. (UPDATE... it did it during city driving this morning once and then stopped at the next light, so I guess not it is just officially intermittent.
* I have replaced and adjusted the rack damper from upgrade bolt from MSource
* I have new fuel injectors from MSource (Monark ones)
* My car leaks nothing, not a drop from anywhere.
* I have no vacuum leaks that I know of anywhere, even after 3 weeks of sitting, everything vacuum still works and when I turn off my key my engine stops immediately
* I have for the first time - a minor, tiny bit of smoke from my exhaust almost constantly now that I do not remember seeing prior to the VCV-modulator, rack damper upgrade.
* I have done a recent diesel purge and just used the tank screen filter replacement and hoses from MSource

It started like i said a few months ago and it only happened occasionally. I did everything above prior to it just getting much worse. The thing I fixed when it just got much worse was I replaced the VCV and trans modulator (transmission shifts like a smooth dream know, got the used VCV and new modulator and manuals from MSource, worked like a charm, I mean awesome)... I also at the same time replaced the rack damper bolt and adjusted and it runs fine sometimes but not others. When it does shake it is VERY noticeable and it is a lopey kind of shake not fast and even putting in neutral does not impact it, only increasing throttle helps a little and then fine at higher RPM). All of my mounts are solid but this kind of shake is bad, I fear what it will do to everything.

I have pretty much every manual you have produced so any ideas or what to look at would be most helpful. Maybe something in missed on the damper adjustment? It runs fine sometimes but not others and seems only after prolonged highway speeds so I figured I had the damper adjustment right aside from this. Again it is just worse now so since it is worse now, maybe the damper is wrong?

Help help please... I am sooo close to 617 perfection... Everything else on my car is now pretty much perfect. Sorry if I skipped something that would help. Let me know...

Thanks tons...
Doug in Texas
84 300SD (Helmut)

Forums

Diesel Engine Specific Aid

Chassis Model Number

W126

Start by ruling out the mechanical

Have you inspected the condition of the camshaft and rocker arms. No flat spots or scoring? Then move on to internal engine timing. Chain stretch? If possible try to do a compression test right when the engine is shaking. Can you isolate the shake (miss) to one or two cylinders by breaking loose injector lines while engine running. Once you have ruled out any mechanical problem then move on to the injection pump. You may have a problem with one or more of the delivery valves. Report back your findings.

Good advice

Ok ,

Local shop just pulled compression... it is good across all 5 in fact at 147k he was shocked how good it was. Your comment on timing chain and injection pump are well taken. He mentioned the fact that at it's age, ULSD (all though i NEVER run without additive for that), and just time that he really thinks the injection pump has seen better days. My local mechanic has an all German shop and owns a 617 as well so I kninda take his work for it as well. (Oh also the valve job was just done thanks to MSource guide from my brother and his 617's and he checked it and said the valve adjustment was good too. Figure while I have the cover of I would check that as well.)

If all things point to the injection pump (and it kinda makes sense), what is the right way to get that done? Do you guys do it or have someone reliable who does and what should that cost? I see used ones but that seems like frying pan/flame to me. I would love to have mine rebuilt or get a rebuilt one if that was possible.

Thanks so much for the advice. I have replaced so much on the engine just as preventative maintenance and any remaining problems seem to point to the only big remaining factors of timing chain and injection pump.

Doug in Texas
1984 300SD "Helmut"

Same symptoms here!

My 85 300TD with 157K does the exact same thing. I replace everything you did as well. Adjusted the valves, purge, filters, new injectors, and so on.

My new rack damper bolt is turned almost all the way in. With the engine warm and slowly adjusting in & out it makes very little difference. So I do suspect that my injection pump is failing. Mine runs "smooth" until you exit the highway and stop at a light. Then it is shaking like a washing machine on the spin cycle!

Please let us know if it was the injection pump.

Rack damper done- shakes at idle, I think I figured it out

To the memeber who posted that he had the same problem. I followed Kent's advice and of course it worked. It is not the fuel pump (at least not now that I understand it more I think)

It was the valve adjustment. Makes sense but I pulled it down in order and did the fuel screen, purge, both filters repalced, then pulled the valve cover off and low and behold, I have three touch-tight valves after only about 1 year and 3k miles. Not sure what caused it but I am thinking that cold it is not a problem and why it was doing it after running on the highway is that it gets hotter under extended load and that is when it shakes because of expansion with heat (Kent may check me on that). Cause when the car cools down after a few lights it doesn't do it as bad. I re-set all of the valves again to the correct settings (with my MSource trusty kit and book) and viola. It is not diong it now. I will continue to test it more and more aa it keeps getting hotter in Dallas but man, this not only makes sense (in my own twisted mind at least) but it also saved me rebuilding my fuel pump that apparently old,still has no problems.

Oh btw, my local shop checked my timing chain for anything odd or signs or stretch and say it appears fine so timing is not an issue (kind of expected that, but may just go ahead and replace anyway at 145k miles and 27 years of age since Kent says it is a good idea).

So if you are out there, live by my new personal commandments of the 617.
1) purge
2) replace your filters (I know you just did it 6-12 months ago, just do it)
3) clean you alda and make sure you have no vacuum leaks
4) adjust your valves
5) It is seldom as bad as you think, calm down and re-check everything (this is a new one)

Got so excited I was certain my valves were good and ignored my own rule. I am waiting for my crow to finish roasting so I can eat it.

Respect from Texas and Helmut is happy again...

DougTx
Dallas Texas
1984 300SD "Helmut"