82 240d, auto. Many years ago the owner ran it on WVO, maybe 20 years. I bought it, fixed some drivability problems (trans, vacuum leaks and more to go).


Car starts great, is the smoothest idling 240 I have seen (I ahve two others) and now runs great, quiet, smooth, reasonably peppy. About to put it on the road as DD.


Took it out last week for the day, ran great until on my way home, losing power/speed eventually down to first gear at max throttle, barely running. Then it would start to clear up and accelerate before failing again about 30-40mph. Went through half a dozen cycles before I got it home, poor running for a few minutes, clearing up for a couple minutes. I did notice earlier in the day that a few times at a light the idle was normal 240 shakey, then it would be fine at the next light.


Did a diesel purge this am with both fuel filters. (BTW, the fuel was filled maybe a month ago). Not much return fuel except at higher rpms, but seemed to run OK during the purge. Then about 20 minutes into it, while running the throttle up and down it went into the fail mode and would barely idle at full throttle. Eventually stopped running, very difficult to restart. Got it running after about 10 minutes and seemed to run ok for the remaining purge (except zero return fuel now). Another failure right at the end. Reconnected lines, new filters, cranked but no start. The clear filter did fill up without priming and looks clean.


Ideas? Fuel pump? The intermittent nature presents a problem with any mechanical failure theory.

Any possibility that you may have picked up some bad fuel on the last fill up?? All you need to have a problem is a little water in the fuel. Good luck!!

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96 E300d

Before you get into more serious items, I would check that you don't have any fuel leaks or air intrusion anywhere. I had something similar that turned out to be a tiny pinhole crack in the pre-filter (brand new after initial install). You could also have a tiny leak in an injector return line or even one of the hard supply lines that isn't quite tight enough.

Dkr.

I've experienced symptoms like that, it was always a physical blockage from a clogged fuel filter. I see you've changed your filters though.

Because it stalled during the Diesel purge we can assume the in tank screen is O.K., this means either there's an air leak (especially likely if you have the white handle primer pump) or the secondary, spin on fuel filter is clogged or the transfer pump that holds the hand primer pump is failing .

Let us know what you find in the end .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Purged the air after filter changes, got it started and let it run for maybe 30 minutes, seemed great. Yesterday I started it and let it run for almost an hour, no problems so I took it out. Stopped at PO for a couple minutes, left it running. When I got back in and left I thought I felt a slight stumble but it was then fine, great in fact, so off I went. Got 5 miles down the highway and it quit. Dead, no restart.


The primer doesnt seem to be working on all pumps, maybe every fifth pump it will pull fuel. I am thinking about changing out the lift pump (that the primer screws into) but dont see one for sale anywhere. All I can find is the primer (which I will also change). Kent does sell a rebuild kit and this seems to be the only option at this time?


All that said, I am not convinced the lift pump and primer pump are the problem because of the on/off nature of the problem. When this is "on" the engine runs better than any I have seen. I would expect bad pumps or air leaks to not be intermittent but constant problems.

Other periphial things I'll check is drain the tank and pull/clean the strainer. The fuel in the clear inline filter looks great so I dont think fuel contamination is the problem.

Is your primer pump the white mushroom or the newer black Bosch one? If you haven't changed to the newer style, the mushroom is probably leaking. The intermittent problem is totally consistent with a slight leak somewhere or air in the lines.

Dkr.

While reading your thread.

Besides the current issue. I might want to check the timing chain stretch. Delayed timing might make the engine sound quieter. You should also check the valve clearances. If they are tighter than they should be might be quieter as well.

Good things to check on any recent acquisition anyways. . Probably fine but still worth a check. I only mention this because you have two others you are comparing it to.

Agree on checking timing chain stretch and adjusting the valves. When “dialed in” these engines produce a distinct sharp clacking sound. This is separate from the no start issue but is good maintenance.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

You also might want to try running it with the fuel cap off, if tat fizes it, check the tank vent underneath the car, let side in front of the tire .

There's supposed to be a rubber bulb you can *gently* squeeze, it crumbles easily, I often find the 'lips' on it are stuck shut .

If the vent pipe is open with no rubber bulb, check to see if a mud dauber wasp hasn't make it's nest up in it ~ you can make a screen to cover the open pipe end .

Blocked/clogged / etc. tan vents cause a slow build up on fuel tank vacuum that will slow or stop the fuel from reaching the lift / transfer pump .

Agreed that the white knob primer pumps should be discarded even though I prefer how they work .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better