I need help solving an issue I have with my 1996 Mercedes 300D. My experienced mechanic has run out of ideas for trying to solve my problem. It seems to be fuel related. The car runs fine when it runs. This winter I was having problems with starting. If I used the block heater, it would start, run for about 1-2 minutes & start sputtering. If I held the accelerator down, keeping the car at 3500 rpms +, it would get through this sputtering but it created a tremendous amount of white/blueish smoke. This would go on for about 3-4 minutes until the car warmed up. Once it was warm, all was well. Then, recently, it would conk out after running for maybe 15 minutes or more. The fuel tank is full, we've replaced the filter & there seems to be no restriction between the tank and the filter. If we re-prime the filter, it starts right up but stops again in 15 minutes. The "check engine" light stays on although I can reset the main light using the dash button. Any ideas?

Have you tried removing the fuel cap to verify it isn't a clogged fuel tank vent?

It is something that could be overlooked but yep, we thought of that.
Thanks for the suggestion.

It might be best to describe and list what you and your mechanic have done so far. Otherwise all replies will start from scratch.

For example have you put a clear hose from the return valve on the injection pump into a container with the end of the hose submerged to see if there is a lot of air? Or you are just running out of fuel? Or elevate the rear of the car substantially to see if a change occurs.

Although this running for fifteen minutes normally and quitting made me consider a few items. All the white smoke is probably being caused by air. If no air was showing in the return line test I probably would monitor the fuel pressure between the secondary fuel filter and the injection pump. No sense fooling around with this problem. You have to find out what is going on before you can fix it.

Or is supply pressure so low there is nothing coming out of the return line? Did you bypass the fuel heater in your checking? Have you established in any way the lift pump is not very weak? It may expedite things. If you have a service engine light what codes are showing? As I mentioned earlier making a list may expedite things and welcome to the site.