PeachParts Mercedes-Benz Forum - View Single Post - Little or NO power after bottoming out suspension- 1981 300SD

JimSmith · #2 03-10-2013, 07:15 PM

Interesting thread. Quite frustrating to get through the 160 some odd posts and finding no solution.

I hate to be argumentative, but to run an engine that is consuming more than 35hp in friction and not smelling burning oil is a bit hard to conceive of - in fact, it would seem not feasible to me, especially if the load is supposed to be coming from a single main bearing. The normal friction losses for this device are miniscule compared to 35hp. There is no where near the oil flow to keep the machine from melting the babbit on the bearing shells for that kind of load. So, take the oil filter out, cut it apart and inspect the element (the main flow element, and the bypass section) for particulate metallic particles. They will be there if the bearing spun. Or any other source of unusual metallic part wear is contaminating the oil system.

I would suggest if there was a 35 hp or so load on the engine at 2000 rpm or so, there would be some good smoke coming from the tailpipe and the turbo would be beginning to pump out some measurable net intake manifold pressure. And so would a lot of oil smoke if there is a friction load of that size inside the engine that would be obvious with the valve cover cap off.

The problem, if it is friction or accessory load related, the mechanism is speed sensitive. Without the AC on, the bulk of the rest of the losses from belt driven accessories are tiny, even the water pump load is tiny at this rpm (it runs on a cubic curve for speed vs. power, so at less than half speed, the load is less than 12% rated - for this to be 35hp the pump would have to be noticeably difficult to turn by hand, and the same is basically true for the rest of the accessories - in the off position the are idling on a shaft).

The problem is either friction related, and that seems unlikely, but it does fit the trend of increasing load with increasing speed, or it is fueling which also fits the bill because if the fuel delivery rate is limited the engine will speed up until the engine speed limit at that fuel delivery rate is reached, and then stop.

I have had a lot of problems, without bottoming the suspension, with these era throttle linkages. I am less familiar with the 617 turbo engine, but the linkage system appears to be similar to the 240D of the early 1980s. This system has a number of direction changes (from foot actuation to injection pump lever actuation) and a series of devices that can be damaged, and only become apparent by tracing poor engine fueling to the various joints.

I know it sounds like covered ground, but I would disassemble the entire linkage and inspect it, then reassemble and adjust per the previously linked instructions. The same with the ALDA and the associated manifold pressure control system. Old, cracked lines will not get a pressure signal to the ALDA and there will be no fuel enrichment as rpm and load increase. In fact, given the age and the brittleness of the vacuum lines, it is probably a good idea to inspect and replace any and all vacuum lines. A shock load can easily damage these lines.

Interesting thread, hope the solution reveals itself soon.

Jim