Won't stay running volvo

My 1990 Volvo 240 starts but will only stay running if I flip a metal tab in the fuel pump relay back and forth quickly. When I stop, the car stalls. What can I do?

I am puzzled by this one because I am familiar with the fuel pump relay on a 1990 Volvo and there should be no metal tab on it. Perhaps someone has been doing modifications, in which case, it needs to be put back to its original configuration.

On this car, the ignition computer, which is behind the kick panel to the right of the passenger’s right foot, supplies the electrical ground to the fuel pump relay, which is above the passenger’s right big toe. It supplies this ground for the first two seconds after the key is turned to the On position, and all the time that it detects an ignition firing pulse.

The reason it is designed this way is so that it removes the ground to the relay and hence shuts off the fuel pump if the engine stops running (e.g. after a collision).

The fuel pump relays in these cars typically last about 10 years, and the ignition computer in a 1990 typically lasted about 15 years (that was not the best year for ignition computers). I replaced both the relay and the computer in my 250k mile 1990.

The failure point in the ignition computer is the transistor that supplies the ground to the fuel pump relay. There are shops that ‘rebuild’ these computers. They probably won’t want your old computer as a core as the market for these units is drying up fast. Any on-line parts vendor will sell you a rebuilt computer for your car. They may want to know the color of the label on the computer case so they sell you the correct computer. The replacement does not necessarily have to be the same color as yours, but they know which ones will work.

I hesitate to tell you how to test and diagnose the system because if someone has been modifying the system, all bets are off, and it may be neither predictable nor safe.

Try replacing the relay and see what happens. If it appears to have been modified, you really should have someone familiar with these cars put it back in order.