Intermittent power loss in a way I haven't seen described
 

My '83 300CDT has been acting funny, with an occasional power loss when accelerating that I haven't seen described elsewhere on the forum.

Between one stop light and another I might have completely different accelerating power— Accelerating from a stop with the pedal mashed, I might get good acceleration...and then literally accelerating from my next red light it is just slow as molasses.

I changed both fuel filters and the throttle bushing at the firewall appears good. The throttle linkages *appear* to be okay, from what I can tell. I'm baffled. I've seen intermittent acceleration problems described elsewhere (like this, for example) but seems to present very differently from mine.

Ideas?

Boost line problem? Either a plugged line or a electrical short to overboost valve/bad sensor

Just a guess

You can try to test it by temporarily bypassing the overboost protection valve straight to the alda. Also check if the boost line fitting at the manifold isn't filled up with junk

Check your boost pressure too

Check as christuna said and the small 90 degree hose toward the top back of the injection pump.

I have been having the same issue, especially after a period of several weeks between drives. My problem usually occurs just once after a couple miles of driving. Lasts 20-30 seconds; can't get over 2000 rpm with the pedal on the floor.
'82 300D, 191k miles.

To start diagnosing this I would install a fuel pressure gauge (either electronic or a hose to interior) and start driving.

Look up the fuel pressure gauge issue. Even with a liquid dampened gauge the needle osculates so much you can only get an approximate reading. Also because of the Plastic Lines you cannot easily T into the lines.

Two methods to reduce the needle osculation is a restricted fitting/orifice or someone made a pressure damper similar to one used in plumbing to eliminate water hammer.

If the Fuel Pressure Relief/Overflow valve can be taken apart you can stretch out the spring till it has a free length of 27mm. Inspect the Ball Bearing that is used as the valve for pitting.

Have only 1/2 tank of fuel and dive without the Fuel Fill Cap. If that fixes the issue it is your Fuel Tank Vent system not working well.

Have at least 1/2 tank of fuel and swap the positions of the Fuel Inlet Hose with the Fuel Outlet Hose at the fender well. If that fixes it your Fuel Tank Screen is restricted.

The fuel pressure test might or might not tell if your Lift/Fuel Supply Pump is working well. I say might because it could be either the pump and or the Lift/Fuel Supply Pump.

Air in the system? The old style hand primer?

I have never tried it but if you T into the Fuel Inlet before the Lift Pump there is a vacuum reading in the manual. A low reading would indicate the Lift Pump is not working well an high reading would indicate something is restricting the fuel from the fuel tank. If the vacuum reading gets high fast I would suspect the Fuel Tank Screen.

If you are getting a high vacuum reading slowly increases and you remove the Fuel Fill Cap and the vacuum drops suddenly I would expect a Fuel Tank Vent issue.

To Diesel911: he only needs an approximate reading to tell if he's running out of fuel at 2k rpm. So a small needle jump is ok.

A regular pressure gauge should work.

could also be sticking brakes. swollen rubber brake lines not allowing the brakes to release for a while after a stop.

Verify that the rubber isolator in the fuel rod ball-joint on the firewall hasn't split. Happened to me. I wondered why flooring it barely let me drive 30 mph. Thought I was running out of fuel.

I would start with the tank strainer.
 

Perhaps a full tank of fuel might reveal an issue there without getting close and personal with the strainer. I might loosen the tank cap and see if venting is a problem. I really like starting with the quick and easy things first though there are many idea presented here it seems many are leaning toward a fuel issue being the problem.

Agree.
 

New brake lines make a man feel good about driving a car that three or four decades old. It's a good time to flush the braking system too.

Air , fuel, then compression .trans issues , brakes would be an obvious smell and heat .Air flow is a good start , an air filter check .youll also want to check carbon buildup in the intake tube , it’s common .

For fuel it’s all filters , 3 on the car .keep the small primary at the pump in check once a month if driven regularly . If you don’t see any build up over time you got a clean rust free tank and have a good supplier you’ve been purchasing diesel at fill up .

Compression is a good time to check your injector health , if you can get a pop tester , it’s a worth while investment with ownership . I would say these engines are maintinence friendly , once you become a fellow mb head it seems That you look forward to wrenching on them . Peachparts is the mothership of information with plenty of threads to search off of and inspiration from followers and gurus .

Last week I thought for sure I bought some bad diesel , an occurance I was feeling shortly after a fill up .At take off the engine would shutter slightly then clean up . Some futher wrenching I found the issue , an oily air filter over due for a fresh one .