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1991 Volvo 940 Turbo Wagon died on me once again

I was driving my 91 Volvo 940 Turbo Wagon yesterday morning when, out of the blue, the warning lights came on and the engine shut down. I was still able to utilize the wipers and radio as I sat there for an hour waiting for a tow, but whenever I attempted to start the engine, I got a few rumbles but the engine would not turn over. All belts seem to be in place. I just had the water pump replaced. I replaced the alternator 2 years ago when I first bought the car and installed a new battery about 1 year ago.

Any thoughts on what could be the root problem here?

Thanks!

A few rumbles suggests that the engine was at least turning over.
There’s not enough information to make other than a wild guess, but I’ll guess the fuel pump.

Sincere best.

Try spraying a little starter fluid into the intake to see if that helps get it started. If it still won’t fire then you most likely have an ignition problem. If the engine does try to run and dies again then check for a fuel delivery issue.

If the problem points to ignition, the ignition module may be faulty. On Volvo’s of this era, this is a small electronic module on the fender skirt wall behind the battery. They are known to fail like this.

BustedKnuckles is correct that module may be faulty, but I would expect to find it inside the cabin on a '91, around the glove box or behind the passenger side kick panel. Also, if the module has failed, it is unlikely that you have lost spark. The much more common failure is that the transistor in the module that supplies ground to the fuel pump relay has failed. Rebuilt modules are available on line, and generally all they did to rebuild it was to replace that transistor. You have to be careful to get the correct module for your engine, transmission, and whether your car is a California or 49 state car.

The most likely failure, however, is a bit less expensive. The fuel pump relays in these old Volvos fail so routinely that some owners carry a spare fuel pump relay in the glove box. I replaced the fuel pump relays in both my '90 and '91 Volvos. I replaced one of the engine control modules.

Finally, there is the crank position sensor. On the back of the engine, stuck in the top of the bell housing, is a sensor. The insulated lead from that sensor runs up the narrow gap between the back of the engine and the firewall. The insulation on that lead gets old and flakes off after a few thousand heat cycles. When the shielding is gone, EMF from the starter and ignition interfere with the signal in that wire and the car starts acting up. Eventually the wire shorts against the engine and the car stops running. Replacement crank position sensors have better insulation that does not fail. If yours has not been replaced yet, it is about 10 years overdue. The reason this is my third suggestion is that yours has likely already been replaced.