Sudden Knock/Rough Running '92 300D?

Can anyone tell me what might be causing this problem? I have a 1992 300D with just over 78000 miles on the clock. The engine has been
running smoothly, and I've got good oil pressure. I change the oil religiously (synthetic), and servicing has been strictly by the book.

When coming back from lunch today, driving at about 30 miles per hour, a knock started (almost like the normal clatter when the engine's cold but more pronounced), and the engine started running rough. I was a block from my office, so I crept a block and a half further and parked the car, which is now being towed to my mercedes shop.

Aside from something major, like a rod going, could this be symptomatic of something as simple as a fuel injector going bad, or getting clogged? I try to put regular highway miles on the car, but it does see a lot of local driving.

I hate to think of the cost of a replacement motor for this car which could run to $8000.

TIA for any and all suggestions/info,

--Duncan

[Benzmac]

We have had a similar experience where some lifters failed and the thing made one hell of a noise. The other thing could be that some of that gunk broke loose from the EGR and is in the combustion chamber...

One more thing that I have seen is that the windage tray bolts will fall out inside the oil pan and kill the oil pump.

------------------
Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Well, I got my answer today, and fortunately for me, it wasn't the $8000+ answer!

Turns out it was one very badly blown out injector on the #2 cylinder (the tech said it was blowing bubbles at idle), so the tech
swapped them all out for new stock units, and the problem was eliminated.

The Master tech at the shop said it would have been extremely unusual for such a young motor (78K) to suffer from a mechanical failure (especially with this model motor), and was also surprised that the injector had blown out.

A check of the injector pump and injector pump timing showed them both to be OK, and the timing chain slack was still only 2 degrees.

Total damage was $385 for the injectors, plus new fuel filters, plus labor.

Guess I'll just have to wonder what ate my injector(s)...

--Duncan

Arrgh. It's not over yet. When the master tech went to test drive the car, he noticed that it was overheating. Then he noticed the bubbling in the coolant overflow tank.

Now, it's compression test time, and yank the head to see what the hell is going on. Now I'm wondering about water in the fuel as a possibility for what caused this.

If I'm very lucky, this will be a blown head gasket, and I'll walk away for about $3K, counting the gasket, new injectors, labor, etc...

--Duncan