Car will start, but it will flood all the cylinders due to a continually running fuel pump. When I turn it on, the fuel pump will not stop after the prime time, and keep going, even when I turn the ignition key off. I have to disconnect the battery to stop the fuel pump. I removed all the spark plugs and flushed all of the gas out of the cylinders. After that, the car starts, and dies after a few seconds when it gets flooded again due to the fuel pump not stopping. I replaced the fuel pump relay, and it didn't change anything.
What sends the signal to the fuel pump to stop it?
Any suggestions?

 

The fuel pump should never stop when the car is running. Now, the fuel injectors should not be open all the time. Maybe the fuel INJECTOR relay is bad.

 

the ECU controls the fuel pump via the fuel pump relay.... the ECU should turn it on when it sees timing pulses coming from the ICU indicating that the engins is moving, and it should turn it off about 1 second after the engine stops turning.

the fuel path is a closed loop, the pumps pump gas into the fuel rail, and the fuel pressure regulator lets any excess fuel pressure return to the gas tank.

 

When i turn ignition on engine not running for the first time fuel pump runs non stop,i was under the inpresion that the fuel pump should star and stop after a few seconds,if i turn key of pump keeps going,then i turn ignition on one more time and turn ignition of and the second time i turn ignition of fuel pump stops.I have to remove spark plugs and turn engine to clear cylinders from gas.Does any body knows who stops fuel pump when you turn key on engine not running after a few seconds?

 

the ECU turns the fuel pump on and off via the fuel pump relay.

even if the fuel pump is running, the injectors should be closed, so no fuel should be getting into the engine unless the engine is running.

 

The injectors are working all the time when ignition key is on,who sends the signal to the injectors to make them stop.If i unplug the radio supressor relay the will stop.I switch those 2 relay and i still have the me problem.Is the somewhere to buy original volvo repair manuals?

 

the injectors get their power from the 'radio suppression' relay, which comes on with the ignition. the ECU (fuel injection control unit) pulses the other side to ground to turn the injectors on on. they should be OFF until the engine is turning over, and then only briefly pulsed to ground each half turn of the engine, where the width of that pulse controls how much fuel is delivered.

if they are always on, then either your ECU is blown, or the wire between the ECU and the injectors is shorted to ground somewhere. its a grey wire from ECU pin 18, goes through connector C (8 pin connector at the right suspension tower) pin 7, then is forked to all 4 injectors. the other side of the injectors is green wires to a junction to a green-red wire to connector C pin 6 to green-red to "radio" relay pin 3.

[note those wire colors and stuff are from my 1992 LH2.4 book... the ECU pin will be the same, no guarantees on connector "C" or colors]. My 1991 book si the same, but I don't have a 1990 book.

If you have Regina injection, its the same, but there's also a 5th 'cold start' injector controlled by ECU pin 32 and a grey-black wire..