I just got a '91 740 with only 89,000 miles that ran absolutely beautifully for 3 hours yesterday, but come this morning, it just turned-over endlessly without any sort of ignition at all. The fuel pump was very recently changed, and I can hear the pump priming for a second when I turn the key.

After several tries and plenty of cranking, I pulled a spark plug to check that, and it was completely dry and producing a good spark, which basically tells me there's no gas getting to the engine.


I have two theories (again, this car is MINT, very low miles, and drove impeccably for 3 hours yesterday)

1) There was moisture in the line because it has probably been used sporadically until now, and it froze overnight and blocked the line

2) Bad ECU? I assume it wouldn't be a relay since it primes right up, but I could be completely wrong


It's a nice day out today so I might actually know if it was a freeze in the line pretty soon, but I figured I should get this out there regardless.

Thanks for any advice!

 

It's 50 degree out and still not firing, so I guess we could rule frozen moisture in the lines out. When my friend gets back, it's on to spraying some ether in the intake to see if anything happens. If anyone has been in this situation, any direction is very much appreciated! Thanks


My buddy that's helping me is a longtime Volvo lover, and the first thing he said is "man, this thing is immaculate"

It's gotta be something stupidly simple, because everything looks perfect that we can see

 

No spark now.. What in the world is going on??

 

There are several items to check. First to check out the fuel, when you turn the ignition switch to the II position, do you hear the fuel pump run? You should be able to hear it. If not, you need to check out why the pump does not run. Most likely suspects are the fuel pump relay as they tend to acquire tiny cracks in the solder joints of the little circuit board of the relay.

For the spark issue I would check the crank position sensor. This sensor provides timing information to the fuel injection computer and the ignition control unit. This sensor is located on the top of the bell housing where the engine and transmission meet. It has a thick black wire that looks like coax cable. If the insulation cracked and flaking off, it probably is intermittent and needs replacement.

This is by all means NOT a complete list of items to check. Just the ones I would start with. Good luck.

 

note that the fuel pump will only run 1-2 seconds on key on then stop until the car turns over. when it stops cranking over the pump stops 1-2 seconds later again.

 

Thanks guys- At the moment I think the crank position sensor is the culprit, as it is indeed torn wide open. There's a new one coming from Amazon now, I'll let you know if that was it

 

5 minutes to install a crank position sensor, and she turned on like nothing had ever been wrong

I do have another question now though- the gas gauge never worked from the moment I bought the car, but after this down time it suddenly came back to life, before staying down again starting the next time I turned it off. Does that sound like a relay/loose wire issue?

 

the gas gauge has no relays involved. the sensor is in the gas tank next to the in-tank fuel pump, and it provides a variable resistance on a pair of wires that goes directly to the gas gauge in the instrument panel. The brown wire is grounded at the instrument panel, and the grey-white wire goes to the actual gauge, which also is connected to ignition switched power via a on-circuit-board fuse. the gauge applies a voltage to the sender unit, and measures how much current is flowing, this is what shows on the needle.

the sender wires pass through two connectors, connector C in the luggage compartment, and big block connector "B" at the left A post. they are connected to the instrument panel on connector C:3 (grey-white) and C:4 (brown/ground). The instrument panel is grounded at connector D:3 and gets its power from D:4 (Instrument panel connector C: is the larger one over on the fuel gauge side, while connector D: is a small one in the middle).

 

Thanks Pierce, doesn't get much more detailed than that! Will go through my car the next sunny day we have