I have a 1995 Volvo 850 GLT that won't start. The engine cranks and the spark plugs fire, but the engine doesn't catch. When I turn the key to POS II, the fuel pump is silent. I first though it was the fuel pump relay. I shorted pins 15 and 87 on the relay socket, but the car still didn't start. Using a multimeter, I verified that the pump was getting 12v from the wire harness. Then I tried tapping on the gas tank with a rubber mallet. I can get the car started this way, but it will die again if I don't keep my foot on the accelerator. While the car is on I can hear the pump going. So the pump still "works", but it doesn't seem to be able to start the car or work without me depressing the accelerator. Is this a bad pump, or some other issue?

 

I would say bad pump.
Try to verify fuel pressure.