Plan of attack on the E300 (fuel starvation and ping type rattle)

[TylerH860]

I've decieded to make this a dedicated thread to aid those in the future and to also perhaps attract fresh folks who didn't see the problem in Jimmy's old 6+ page long thread on the 1995 E300. Note this is the same motor for 96-97 E300 diesels.

Problem:
When tempuratures get below 45* the car displays the classic symptoms of fuel starvation. Startup and idling is effortless and quiet, along with getting off the line from about 0-30 MPH. Once it hits the rev range of about 2500, a rattle noise (sounds like dieseling and pinging together, certainly not valves) starts in and gets nasty, bogging down the car. If I am light on the pedal then I can get a steady acceleration to 70, but if I floor it the car will stumble and struggle to 40. There is only a slight improvement from a cold engine to a warm engine, which I suspect is just the natural way these cars are based on most of the others I've had.

If the temperature is above 45* this problem is nearly non-existent. Only at the highest rev ranges of a WOT do you start to here the rattle (faintly) and a very slight cut out before the shift.

The effortless cold start and smooth idle and launch eliminates glow plugs (which were recently tested), compression, top end, and injectors, in my opinion. Recently the heat exchanger was replaced along with the primary fuel filter and a leaking fuel line. This was shortly before me purchasing it.

So far we have 4 theories:

1: The secondary fuel filter has not been changed. Cold fuel is thicker thus harder to pass through the clogging fuel filter. While it seems strange that it would only be showing ill effects in the cold this is always the first step in diagnosing a fuel starvation problem. It does not explain the rattle, as in the past I have not heard this noise when I had bad fuel filters. Also, fuel filter problems are usually more rapidly degenerated and this problem has been consistent for 2 winters now.

2: Failing lift pump. Colder fuel is thicker and harder to send to the IP. This also seems odd since due to the temperature change and rattling. Also, the issue seems unaffected by hills. Whether I enter an uphill on-ramp or downhill on-ramp the problem remains consistent.

3: Air is getting into the system via leaky fuel line or delivery valve o rings. Once again, this does not explain the temperature variation and rattling. There is also no visible leaks or a fuel smell associated with this issue. Colder air would be more dense and harder to get through a leaking fuel line.

4: Injection pump timing is off. Over the years a timing chain stretches and slowly takes the injection pump out of sync with the engine. The rattle is a classic symptom of retarded injector timing. With the colder being more dense and oxygen rich, it exacerbates the issue with the injector pump timing. While diesels don't have the electronic compensation that modern gassers and later diesels have, could cold air make that much of a difference?

I believe number 4 is the most likely scenario, but it could also be a combo of number 4 and anything.

Any other ideas?