My 90 740T won't start.

On my way to work, the car stalled, no power, for about 1 to 2 secs. Then came back suddenly and the rest of the trip was fine.

After work, the car wouldn't start. It cranked and cranked and tried to catch, but wouldn't run. I started to pump the gas pedal and began to smell fuel. But no action. I thought, "no spark".

Towed the baby home. Read FAQs forever and I've deduced the following:

-I've got spark at plug cables
-I've got spark at coil

-the "pre-fuel pump" runs with key on (the main pump only runs after the engine engages, right?)
-I hear all the usual relays. Yes, well it doesn't "sound" any differant than normal
-the pressure regulator does not spray fuel through vacuum hose, that suggests that regulator may be fine.

-the engine cranks fine but won't engage
-I tried to overpressurize the fuel system (by turning on the pre-fuel pump) by turning on the ignition a dozen times before attemting to start engine and it seemed to help, in that the motor nearly caught, but that was all.

WEIRD PART

-I removed the fuel cap
-cranked the engine, and it came alive, then ran horribly while I pumped the gas peddle to keep it going
-It died. Cranked and it wouldn't engage again

The fuel cap is less than 4 months old. NAPA part tho', and the car has run perfectly for the last 18 months (since I've owned it). Lost gas cap 4 months ago.

So I have a fuel problem.

Is it the pre-pump or the main pump?
Is it the main pump relay? Pre-pump relay seems fine, since it works.
Is it the pressure regulator?
Is it the ECU (god, no) with a faulty pump relay circuit thingamabob?
Is the cap wrong? Haven't had any problems for 3 months and 29 days with new cap.

This came out of nowhere. No warning, so I'm thinking a part that just suddenly went. Sounds electrical, doesn't it. Where do I start?

Thanks you guys.











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Mike in California '90 740 Turbo Wagon - Hydrogeology Field Vehicle

My 240 did the same thing when i first got it.Thing wanted so bad to run, but it wouldn't catch.Replaced all sorts of fuel and ignition system parts, to no avail.I was about to call the junkyard, when it came to me...try a new AMM. Now, I just happened to have saved one from my old 760, and the part # was the same. Plugged it in, went to start, and she ran like a dream.If you can find a used one in good shape for a fair price, I'd recommend that. Or maybe you have a friend who'll let you borrow theirs for an hour or so, just to see. Good luck.

Pardon my ignorance, but AMM? I don't know what that is.

Thanks a lot for your post!

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Mike in California '90 740 Turbo Wagon - Hydrogeology Field Vehicle

Sorry- air mass meter. The little black tube thingie with the plug that goes into it-it should be right on top of your airbox. Sometimes the little wires in the tube break, that's what hapened to mine, and it no longer sends the right signal to the computer(or any signal). See if you can find a used one cheap. Good luck!

When you are cranking the engine look and see if your tack moving. If you are getting a tach signal (ignition) the tach will bump slightly when cranking.
Things to check fuel pump relay (fuse box area), radio suppression relay (on radiator reservoir), and Crank position sensor/rpm sensor (on the top of the bell housing). This is a tuff one because it fails intermittently. You can use diag port to check to check the cps. Power pack (on driver’s side fender).
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90 744ti, airbox, K/N, G-Valve, VDO, modified exhaust.

Check the fuel pressure regulator. Pull the hose off and check for gas. If so, bad regulator.
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Warren Bain - '86 744Ti M46 >290Kmi, '99 V70Glt > 45K mi, '96 965 >100Kmi Wifemobile near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu.

I've had similar symptoms with the failure of the LH-Jet temp. sender. If, for the few moments it runs, it's running REALLY rich, check it.

failure mode: an open circuit (failed sender) makes the ECU think it's REALLY cold outside. The ECU then richens the misture as much as it knows how.