My sister has a 1991 Volvo 240 Automatic Sedan that has developed a no start condition. We've been trying to find a local towing company to get it to my house and have been tiptoeing around her condo HOA doing some limited troubleshooting (not allowed to keep the hood open for more than 15 minutes) in the meantime. She was out and about running errands a few days ago when her car would crank, but not restart. I suggested she change the system relay (fuel pump relay), as my experience tells me that's one of the first places to start. Her car did restart after that, and drove home. A couple days later, the car would not start again.

The car never fails to crank, and about 1 out of every 5 attempts will fire off for a few rotations. I originally suspected that the replacement relay may have been at fault. Both the replacement and old relay actually function perfectly on the bench. I metered the relay connector (with the relay installed) with the key in position 2, and the engine computer is not connecting pin 20 to ground which has the effect of not running the fuel pumps. See the attached wiring diagram snippet for reference as to which side of the relay is closing. I also removed and tested the ignition switch, as I understand that this is a common failure point. All of the contacts measure identical low resistance values when configured in position 2. I also (when the HOA lady briefly left her porch) pulled the crankshaft position sensor connector and made sure that when cranking it was outputting AC voltage. I will be unable to attach an oscilloscope until we can get it back to my place.

Obviously, if this no start condition doesn't have a cause the community is familiar with, and when I can actually get the car to my garage, I'll go down the dumb troubleshooting path as if I had no idea what the problem is. But I wanted to find out if there was any documentation about what conditions need to be true before the ECU will choose to activate the fuel pump, since fuel is a component of the fuel-air-spark mix and I know for a fact it isn't present.

 

ECU will not activate the fuel pumps unless it sees pulses on the crank position sensor.

The next time it has the no start condition, check to see if you hear the main fuel pump run when the key is initially turned to the II position. It should run for a second or two when the key is turned from position I to position II. If you don't hear the pump during this time then the problem is most likely the fuel pump relay or the ECU (or the pump but they rarely fail intermittently).

 

To quickly know if it's anything caused by fuel pump/relay, use paper clip to jump all fuel pumps and try start, if starts, then something is happening to the control system. If doesn't start, then its fuel pump or fuel pump power supply.

To fully test the ECU, test it while cranking. I heard it somewhere that certain 240 ECU has issue about when to activate fuel pump. Mine for example, won't activate until I crank it so it takes 4~5 crank cycle(1~2 sec) to start.

Also, have you checked the big 25A fuse in the engine bay? That thing been loose or corroded, will make all kinds of interesting none start/stall problem.

Cheers!

 

The Bosch LH 2.4 and LH 3.1 fuel injection ECUs always ran the fuel pump for 1-2 sec when first powered on and would shut off if it did not detect pulses on the crank position system. LH 2.4 started in '89. Since the OP has a '91, he should have either the LH 2.4 or 3.1 version. There are early "pink label" ECUs for LH 2.4 that had problems with the fuel pump circuit that would fail prematurely and not run the fuel pumps. These "pink label" ECUs were mainly used in '89 so most likely shouldn't be a problem in this case. '90 and later model years used a "white label" ECU that did not suffer this weakness. I have only heard of one failure of a white label ECU failing in this manner.

Earlier versions (LH 2.2 and earlier) did not run the fuel pump when the key is turned to the II position.

 

Ya, that make sense! Mine is 89 with a purple/pink tag on the ECU. It never kicks fuel pump in without cranking or jumping.

 

I had the same problem with my 89 740 gl. We hot wired the FP and it would run . After doing some searching I found the complaints about the ECU and decided to get another one. Found a rebuilt one on ebay and it did the trick. Car runs great with 417K miles on it . I also recall there were several different ECU's that would work but don't remember which one. As a side note I would like to know who rebuild these ECU as I kept my old one and would like to get it done.