617 Turbo diesel Low Power at low RPM

I have a 1982 W123 with about 240,000 miles. It runs great at normal highway speeds.
The problem(s) are first at low RPM it takes a lot to get the car going, it can be floored and barely start to move. The other day my wife parked on a hill and when leaving it took a long time for her to move. (transmission is good, just replaced) Power is excellent when rev's are up, it will actually chirp the tires when shifting gears.

Second problem (could be related to the first) If this were a gas car I would think it had a vacuum leak. At RPM between 2000 and 3000 it will not stay in one spot without moving the throttle. It will not keep at one RPM.

Any help on these problems would be appreciated.

klbarton

Forums

Diesel Engine Specific Aid

Chassis Model Number

W123

1981 300SD low power good idle

I have exactly the same problem with my 1981 300SD. I just rebuilt the injectors (it wouldn't run at all) and it now idles fine and you can rev it up in park normally. But when I put it in drive and step on the pedal it acts like it is getting no fuel at all, it just stays at idle. Put it back in park and it will rev up normally. If I ever do get it going and get it up to speed it will run fine until I slow down again. Both filters are new. Maybe someone can help both of us.

Low power at low RPM 617 turbo

Is your car starting out in 1st gear? I have read where this can be a transmission thing and since it is starting out in a higher gear that is will seem to be like when you mash the pedal down that nothing will happen. I had vacuum leaks that casued mine to behave this way and now that the leaks are repaired and I replaced my EGR (another source of leaking) my car actually starts out in 1st gear and accelerates much stronger. Try this... get your car going about 30mph and then let off the gas... then push the pedal all the way to the floor. Does it "kick down" to 1 st or 2nd gear from third? Or does it just struggle again to accelerate in the gear it is in (most likely third).

I know there are trouble shooting source guide books on the site to help with this. My local shop just has a lot of experience with 617's and when doing some other misc stuff for me took a look and repaired my issue and explained to me.

Vaccum problems are the devil and they cause problems everywhere in my experience. Take the time to get some golf tee's and a vaccum gauge and vacuum pump (you can buy them here) and figure out where your problems are. It is a great palce to start and once they are traced down and resolved you can start looking at other things in my experience. Also I believe there is a kick down switch that can also be bad that can cause this. If you have vaccum issues and you try to troubleshoot elsewhere I think of it like hearding cats, it will keep you busy but ultimately may just drive you nuts.

Hope that helps...

Doug
1984 126 300SD

Low power at low RPM 617 turbo

Was looking for someone to sell me Monark injection nozzles. Found so far only sales in USA, which is a little far away from here.
It sounds like you may have a fuel delivery problem. Had the same symptoms with my –82 MB 300 Turbodiesel here in Norway a couple of years ago. When checked, all the filters were rather clogged, especially the one in the tank. Such a symptom, however, really goes back to the fuel delivery pump. Being directly driven by the camshaft of the fuel injection pump, it will have problems in delivering enough fuel at idling speed an lower revs when it becomes weak, and still to pick up enough pressure at increasing revs. The valves of the delivery pump on these cars easily start to leak due to a build-up of residues.
When I changed the filters in the engine room and cleaned the one in the tank, my car started to work reasonably well again. The pump, on the other hand, is easy to remove and a new one doesn’t cost that much either. However, you may try to renovate the two small valves in the pump, something I plan to do on my car.

1981 300SD low power low rpm

These are very good possibilities. There have been issues with vacuum, I rebuilt the pump and replaced some lines and the door locks still don't work but it does shut off now.

I will check the first grar shifting tomorrow.

I never thought about the fuel filter in the tank, the rest have been replaced. More to try.

Again thanks, and I will keep fixing until I find the right solution.

617 Turbo diesel Low Power at low RPM

I ordered and received a new lift pump from this site and hope to install it tomorrow. I kinda felt like that may be a problem.

To Doug:

You mentioned golf tees. I have a few I haven't broken (thats a whole other problem) and really would like to check my vacuum system. I have a hand vac pump. Do I disconnect from my car vac pump and connect my hand pump there? Then unplug the hoses at the sensors and plug with golf tees to see if vac holds? Is this a plan or is there more to it?

Where is the vac pump on a 1981 300SD?

1981 300SD low power low rpm

OK, I changed my lift pump - no difference.

Doug, I did the 30MPH kick down thing and yes it went into passing gear right away. It just does not want to start out pulling on a hill. When it gets going I feel it change gears 3 times for a 4 speed transmission.

OK all you MB guru's, help me out here.....

Did you find the cure? I

Did you find the cure? I seem to be having the same issues of poor low rpm power on my 83 300CD. I haven't cleaned the tank fuel filter and my lift pump was replaced about 10 years ago.

My 83 300SD did this, 20 years ago

Your Alda might need adjusting or cleaning.

My car was doing this at high altitudes, but still ran normally at sea level. I was so alarmed at the slowness, I took it into an Indy and the first word out of the mechanics mouth was, it's your ALDA. After cleaning and adjusting my car performed almost as well at high altitudes as it did at sea level. The car basically acted like it had about 20hp till the rpms finally hit 3k rpm or so, then it would take off. If the hill was steep it could take 30 seconds to go from 0 to 10 mph.

There is also such a thing as a Banjo bolt, that affects shifting. I have no personal experience with them, but I think you are supposed to fix all your vacuum leaks then adjust your Banjo.