I am trying to get my car smogged today but now the fuel pump will not turn off. When the ignition is off and the key is out the pump is still going. There is also a hissing sound in the fuel lines in the engine. How do I fix this???
In a properly functioning car, the ignition switch turns on, then the ECC
(computer) relay, then the computer powers up.
The battery sources the power to the fuel pump through the fuel pump relay. The
fuel pump relay control coil gets power from the computer and the computer
completes the circuit by providing a ground. This closes the fuel pump relay
contacts. Battery power then flows through the closed relay contacts to the fuel
pump.
The computer is programmed to turn the fuel pump relay on and off according the
needs of the engine.
You have one of four problems:
1.) A failed fuel pump relay: relay contacts have stuck closed.
2.) A short to ground in the computer to fuel pump relay control circuit. The fuel
pump relay is located under the driver's seat. The green wire going from the fuel
pump relay to pin 19 on the computer may have a place in it that has rubbed bare
and is shorting to ground. The computer test connector under the hood on the
driver's side of the engine also has a wire that connects to pin 19 on the computer.
It is used to test the fuel pump circuit by grounding it to make the fuel pump run
all the time. If someone jumpered it to ground, it would be just like a short to
ground.
3.) Someone has crosswired your car. This could be difficult to fix, since the bad
wiring could be hidden in a number of different places.
4.) Failed computer - not very likely, since the computers are not prone to failure.