OM606 Turbo Knocks Until Warm
 

It's a 99 model E300. Used to be my mothers car, and I'm going to be buying it back.

It knocks when it's cold, but once it's warm it quiets down and sounds like a healthy 606. Our friend who has the car now replaced all 6 injectors on the car when 1 injector went bad, but oddly enough it still knocks until warm. The whole engine has been taken apart as well and the bottom end is not the problem.

It has to be fuel related, but I can't think of anything else. Please feel free to chime in with ideas, kind of at a loss.

Jake

Bad glow plug? Can you isolate the cylinder that's knocking? I had that problem and I had to re-torque the delivery valve holder.

I was thinking a glow plug as well maybe possibly. But they were replaced 4 years ago when I had the car and it's only had about 10k miles on it within that period of time.

Can you isolate the cylinder like Kartek suggested? Interesting about the engine being torn apart. Do you mean it was really torn down and rebuilt? Why did it need that? Could it be a case of the new production nozzles not being up to snuff? If I ever get my hands on a good set of original injectors I'm going to hang on to them for testing purposes. If you can isolate it maybe swap the injector with another one.

No the engine was taken apart. He was concerned it was something on the bottom end. Nothing was rebuilt or changed while it was apart.

I will take a look into isolating the cylinder, I have a feeling it's the cylinder that had the bad injector. Could the nozzles even still have something wrong? These were brand new injectors ordered from MB.

Car only has 160K miles on it.

Unusual to have problems on a 606 with so few miles.

What I have done in the past diagnosing diesels is with it running, crack the line loose at the injection pump to make the cylinders go dead one at a time, see which one makes the knock quit. Wear heavy gloves, use a long wrench, face shield, and keep back. It will make a mess of course but loosen the line as much as you can with a swing of the wrench, it will take its ability to develop pressure away with the line nut loose enough.

I would still go with checking the glow plugs prior to doing anything else. Easy to do with a multi-tester and doesn't cost a cent. If it is the glow plugs, you will be spinning your wheels trying anything else to solve the problem.

Glow plugs are easy to check by unplugging the GP relay and checking resistance on each of the 6 circuits.

Tick or a knock? Top of engine or bottom end? Consider a collapsed hydraulic compensator (aka lifter) as a possible cause as well.

Not like a lifter when they go bad and do that ticking.. It's more of a knock. Like a fuel knock.

It's nothing major. Doesn't affect the performance, or MPG, or starting ability of the car. It's just annoying and needs to be fixed is all. After replacing the injectors, the fuel economy went back to a regular 35 on the long highway trips that it used to get.

I think this is the first thing I'm going to do is check the glow plugs..