Okay, so ever since the 240D came to us (super-high mileage, half worn out, details and history completely unknown) we've been trying to go through it issue-by-issue and get it sorted out. When we first got it, it had been sitting for over a year and so it had fuel tank scum problems and was impossible to start. We finally got it running, after a 10 minute battle, with WD40 through the air intake. One tank removal, cleaning, chemical treatment, and about eight filters later, the car started running "almost reliably". It was starting up, while not perfectly, well enough to not be worried about it not cranking in a parking lot. Never had to hold the key more than about two to three full seconds before it was running even on a cold morning.

The engine DOES have fairly high blow-by, because the oil cap dances at an idle, and it probably has never had a valve adjustment in its life. Obviously those are contributing factors or at least theoretical contributing possibilities. It's hard to start because it's just slap worn out and low on compression, possibly.

But I can't ignore the fact that we got almost two months of good, reliable, quick starts out of it before this problem started. An engine, even if it's worn out, behaves more predictably than that.

Now, you can hold the key in the crank position for 30 seconds at a time with the accelerator on the floor, with the thing connected to a good battery with jumper cables, and you could crank for probably three full minutes in 30 second blasts, glowing twice until the relay cuts out between each one, before it would run.

That's not glow plugs. Even an engine without glowplugs should start if you're putting that much heat into it just by cranking it over. Especially since I've had this problem consistently on 70 degree days.

What would bring this on so suddenly? I'm thinking fuel delivery. It acts like an engine that's fuel starved during this cranking process -- but the black cloud behind it as you're cranking sort of negates that possibility. I thought it might be an air leak, so I primed the engine with the (brand new) hand pump right before my last start attempt. Didn't make a bit of difference.

It's a 4-speed so I have started parking it at the top of the driveway hill in such a way that I can just roll start it and get moving. Guess what? Works perfectly. Not so much as a cough or shudder when I pop the clutch in 2nd - it just comes right up to life and will IMMEDIATELY idle and run normally.

Warm starts are absolutely flawless. If you let the car sit for three hours or longer, you'll have to toast the starter to get it running again, or push it off and pop the clutch.

Any theories? A few answers, please, in addition to theories?: Thanks

1. Is priming with the hand pump adequate to ensure that fuel is making it all the way to the injectors even if there was a leak in the system? It definitely primes until I hear the relief valve or whatever opening up.

2. If I wanted to do a volume test by pulling the return line and measuring the amount of fuel cycled through in X seconds, what would X be and what quantity am I looking for to prove the IP is adequately functioning?

3. Could low compression and poor valve adjustment really cause that much of a problem cold starting -- without affecting warm starting the tiniest little bit. It warm-starts like a brand new engine.

4. Doesn't the fact that it roll starts so easily and, more to the point, takes less than five seconds after starting it with the transmission before it's running perfectly for the day, indicate that it can't be anything TOO major? Or else I'd pop the clutch, it would spring to life while it had a hill to roll down, and die as soon as I clutched out again?

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL