Been asked to help a friend (nice old guy) of a friend who is getting desperate with his 740 estate. Story is of increasing tendency not to start when turned off or to cut out but then start when left for an hour or so.
On advice the guy has had the fuel pump and the fuel pump relay replaced but this has made no difference - in fact the beast won't start at all now. I understand that the fuel system may be ok but now there are no sparks.

I'd be very grateful for any info or experience - I guess I'd start looking at the engine management system - is it one of the Bosch systems? does anyone have any info on sensor testing? or any other advice to offer

Thanks in anticipation

Bill

Thanks very much to all respondents. Car turned out to be older type 740 with Hall effect unit in distributor. Found that plastic female socket attached to the distributor body had broken leaving all connector weight hanging on the small internal wires and one of these had parted from the connector. I guess that before this it went through stages of shorting out and poor connection which would explain the observed symptoms.

Anyway, as soon as I had repaired it the car fired-up first time (just like a Volvo should)- the elderly owner was amazed & delighted at the no cost solution which I attributed fully to this wonderful resource.

Thanks again - Bill H

With all these cars, no spark also equals no fuel- the computer must get a pulsed signal to turn on the fuel pumps.
For a turbo up to 89, this comes from the hall sensor in the distributor. This does go bad and causes no-start situations. Wiggling the connector at the bottom of the dist may cause the problem, or make it go away. We replaced the dist in our 88 740GLE 2 years ago for this reason.

For a non-turbo 89-up, the same problem stems from the RPM sensor or crank sensor- it has several names depending on who you ask, but basically it looks at a sequence of holes on the outside of the flywheel, and gives the computer pulses that way. The sensor is surely due to be replaced if it's original, in a 1989 car.

There is a power stage mounted in the LF fender, that can go bad and cause no-spark situations. It's a known failure item.

As the FAQ's and many posts on here mention, the fuel pump relay and ignition suppression relay are also potential no-start problems.
Good luck!
--
Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

Bill,

My first thoughts would be to see if it starts with the AMM disconnected. If it does, the AMM is the likely culprit.

The other thing seen in many posts is the RPM aka Impulse Sender, mounted in the top of the bell housing, behind the block. This is the prime source of "timing" for the Ignition Control Unit—and with no ignition signal, the FI system doesn'r function either.

The other ignition "suspect" is the "Power Stage/Amplifier" mounted on the forward part of the left-inner wing (I once owned a TC).

Happy New Year,

Bruce
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67

Could it be the Fuel Pump Relay? I thought this was #1 suspect in this sort of case.
--
'91 740 GL B200E AW70 Estate, '86 740 GLT B230E M46 O/D 7 seats Estate, '89 740 SE B200E M47 saloon, '87 BMW 316 carb Coupe

" I thought this was #1 suspect in this sort of case."

Not with a "No Spark" symptom. Gotta have spark to get the FI system going.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67

The fuel pump relay was replaced anyway, I would check the suppression relay next as it is easy to access(hangs off the coolant reservoir with another identical relay)and wont cost you any money. You can lever the cover off the relay from its base and check the solder joints on the board, if they are cracked resolder them. Might as well check both relays rather than just swapping them, both had cracked joints on my beast. I would also check the intake ducting to make sure a clamp hasnt come loose. Other than that, I agree with the other suggestions and with whats in the FAQ section.

Good Luck
--
Budge - Aussie - 1990 740 wagon - B230FB 225k