I currently have an intermittent starting problem with my 1994 C250 diesel (in case this model isn't available in America it's a non turbo 5 cylinder engine).

The problem is -

For the past 3 weeks, and only first thing in the morning, and about twice a week, it will start but immediately stop. It then takes about 20 seconds of cranking for it to start to splutter into life, then go smoothly. It's only in the morning as it's never done this when I leave from work. It sounds very much like air, as it's the exact same symptoms I'm getting when I changed its fuel filter about a year ago. If it was its pre-heaters I would have thought it would be lumpy from first turn of the key, then go smooth, unless the majority of my pre-heaters are shot!

Since the fuel pipes going into and out of the fuel filter assembly are clear I can see about an inch long air gap in the fuel-in pipe (the pipe from the fuel tank pump to the fuel filter assembly). Do you know if this is normal, or is this a clue? This air gap has been there for months and months, but is it possibly playing catch-up? I park it at night nose up on a slight hill; At work the car is parked on the level, if this helps.

I've been in correspondence with another C250 owner who's had the exact same symptoms. They were advised to change the pre-heaters, but this didn't make the slightest difference. They then took the car into their local MB garage who connected up to the car's 'black box' which indicated it had 3 failed starting problems logged in the computer. These registered faults were cleared from the computer's memory and the owner hasn't had any problems since. I smell a red herring with this as my car's diesel pump looks pretty mechanical. The only wires I can see coming from it are for the fuel solenoid. Also, surely if it was a computer problem the car would be more consistent with its starting problem, rather than the current lottery.

There are no manuals apart from MB authored ones (that will cost the earth) so it's down to intuition or advice from other owners. The small MB owners' manual I got with the car says the diesel system is self bleeding with about a minute's worth of turning the starter key. I feel pity on the starter motor for doing it this way, or can you advise if the starter motor is made of stronger stuff than what I credit it? If it is just air ingress bleeding my dad reckons cars with in-line diesel pumps should have a bleed screw, but access on the Merc is limited with the inlet manifold getting in the way. Do you know of a bleed screw or would you recommend bleeding the car by loosening the metal high pressure pipes?

Any advice?

Apologies if this mail is too long winded.

John Hamilton
Scotland,
Great Britain