power loss in my 300D
 

I've been having a weird power loss issue with my '83 300D. The car runs fine for the first 5 miles, then slows down to about 55 mph. Pushing the accelerator in doesn't make any difference. A few months ago I decided the problem was a leaky vacuum line messing with the wastegate; so I replaced some rubber lines that looked really bad. This fixed the problem for about a month but now it's even worse. I know the fuel tank is venting properly; and the fuel filter is new.

When you say the fuel filter is new, which one are you talking about....The spin on one, or the in-line plastic one. I had a similar issue a while back, and cleaning the tank screen and changing BOTH fuel filters fixed it

Recommend a new tank screen. Found a large hole in the screen on my 1987, had the part on hand. Don't risk having to do the job twice.

Probably a fuel delivery problem of some kind. You could try switching the feed and return lines in the engine compartment. If the problem goes away, it's a plugged tank screen. If the problem continues, the issue lies elsewhere. I wouldn't pull the tank screen before running this test.

That's interesting. Could you explain the concept in greater detail?

Just after I posted my question I read elsewhere on this forum about the inline filter. I didn't know the car had one. It was very dirty. I replaced it, and it seemed to help a little. I didn't know there is a screen in the tank. I'll check that. I really thought it seemed like a fuel pressure issue, but I was out of ideas. Thank you for the advice.

tangofox007- I read about that on this forum somewhere. I'm not sure exactly how it works but as far as I can tell there is a vacuum valve connected to the throttle linkage. A line from this valve connects to the wastegate controller. This adjusts boost relative to throttle position.

Before you pull the tank screen filter (with can be a pain as the tank has to be either drained or empty) do what Kerry posted earlier (see below) Sounds like you are getting closer to fixing it

"Probably a fuel delivery problem of some kind. You could try switching the feed and return lines in the engine compartment. If the problem goes away, it's a plugged tank screen. If the problem continues, the issue lies elsewhere. I wouldn't pull the tank screen before running this test".

Loss of power
 

Suggest draining the gas tank. This is a long shot, but I was having similar problems and discovered someone had put some q-tip swabs into my gas tank. Car ran okay for a few minutes until one of the q-tip swabs got sucked in and blocked the fuel line. Just my $0.02.

I switched the fuel lines tonight and that didn't fix the problem. I took the cap off the tank even though I'm sure it's venting properly and that didn't make a difference either. Is there a way I can put a temporary boost guage or fuel pressure guage on it that I can read while driving?

On the top of the valve cover is a hose that runs to the air cleaner. Remove this hose and check for any restrictions in the hose. As a test, disconnect the hose from the air cleaner and take a test drive. Report back with results.

If you switched the fuel lines and it did not help, most likely the tank screen is OK. How much fuel was in the tank when you switched the lines?

@Bassmaster: LOL . . . reminds me of the days when the prank of putting a condom in the tank would drive the owner crazy and cause the same exact problem!!!! LOL! Wondering if it was done by idiotic mistake . . . or deliberate to the PO.

Since switching the lines did not fix the problem, it is likely that the problem is not in the screen. However, since back flushing the lines is a very easy procedure you might give it a try anyway.
Try the feed line first. Disconnect the line at in-line filter in the engine bay, remove the tank cap and apply the compressed air to the line. Try short shots at first. You should hear a lot of bubbling at the back of the car. Please note that you must have enough fuel to totally cover the screen for the compressed air to clear the screen. If part of the screen is above the fuel level, the air wil take the easy route and not clear the screen.

Some time ago I removed the screen and let the crap go all the way to the in-line filter. This one is much easier to clean/replace than the tank screen.
This is not to say it is the correct thing to do, though.

good luck
gonzalo

Sounds like maybe the lift pump is going bad then. Another member here (Surveyguy, lives not to far from me) was having issues with random fuel starvation, and I pulled a used lift pump for him and it cured his problems.

I haven't had much time to work on it recently; that's why I haven't posted anything. I did blow out the lines, that didn't help. Today I finally put a gallon can of deisel in the engine compartment and connected hoses from it to the pump and return. (Tip for anyone who wants to try this: remove the windshield washer reservoir to make room for that can.) I took it for a drive and experienced the same power loss; though it didn't slow down quite as much ( about 5 mph faster). I think this indicates a weak lift pump. I reason that it ran a little faster because it wasn't experiencing the resistance in the tank screen and the fuel line under the car. Do you agree? I'll remove the lift pump and examine it.

Have you noticed any improvement in performance with a full fuel tank versus an almost empty one?

I dismantled the pump and it looked pretty good. The valves were very lightly pitted. I polished the valves and seats with very fine sandpaper. This made a noticable improvement. It will now hold 65 mph. previously it would barely do 60. Will a rebuild kit fix the problem? I plan to install a fuel pressure gauge. Can anyone recommend a good kit?

I installed one in my '82 300D and you would have thought the engine had been overhauled.

I stretched the spring in the relief valve. Performance is inconsistent now. Sometimes it will hold 65; other times it won't do 60. I ordered a fuel pressure gauge today. I'll install it to see if the fuel pressure is indeed the issue. Can the injector pump or governor cause a problem like this? I haven't noticed that the fuel level in the tank makes any difference.

I might be digressing here but have you performed a diesel purge? Dont forget to prime the fuel filter and crack the injectors to bleed it.

Have you cleaned the banjo bolt on the rear of the intake? How is the air filter?

What condition are the fuel lines in?

What style primer pump do you have? The old style can allow air to be pulled in as well.

x2 on primer pump

Just a thought, check your turbo and exhaust to verify there is no pressure build up causing a loss of power.

Also check the rubber connectors of the switch over valve. These do break, and when they do, the boost pressure signal never reaches the ALDA.

I finally installed the pressure gauge. pressure is consistently 28psi and there's no drop when it loses power. How do I tell whether I have the old style primer pump? and what is the ALDA?

I suspect that you might have confused "wastegate controller" with "EGR valve."

I replaced the primer pump; with no results. I'm just about ready to replace the injector pump. What should I have to pay for a good used one?