Question about 1992 Jaguar XJ6
With the ignition off there is 12v at the input to the fuel pump relay (circuit diagram shows direct wiring from battery to relay). When the ignition is turned on the 12v goes away and the car will not run. Taking a wire directly from the battery positive terminal to the relay input, just as the car wiring should be, the engine runs fine. Could this be a bad connection beteen the batery and relay? Ignition off - no current draw - 12v, but with the ignition on and the pump providing a load the whole 12v is dropped across the bad connection?
I would check the ground for the fuel pump relay that operates the switch side of the relay.
You should have 2 12v inputs to the relay. When the relay gets 12v input, it closes the relay switch on the heavy current side that sends 12v to the fuel pump.
A relay is needed because you don't want heavy current going through the switch.
Also, most cars only run the fuel pump for 2 seconds when the key is turned on because you don't want the fuel pump running without the car running. If you listen closely at the fuel tank, you should hear the pump run for 2 seconds when you turn the key to "ON"
When the key is turned to "START", the fuel pump should run continuously.
The engine computer tells the fuel pump to shut off if the engine rpms are zero.
So, I would check the switch side of the relay. Power amd ground.
Posted on Mar 01, 2009
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· Fuel Pump secondary circuit shorted to power
· Fuel pump relay contacts always closed
· Open in fuel pump monitor (FPM) circuit between ECU and connection to POWER TO PUMP circuit
· Heated Exhaust Gas Oxygen (HEGO) sensor shorted to power
· faulty ECU
Engine Does Not Start:
· Open inertia switch or inertia switch circuit
· Open in or between ECU and fuel pump (This includes open in fuel pump brushes/windings)
· faulty ground connection at fuel pump
The easiest way to check this circuit is to go to the fuel pump relay. If the relay clicks when the key is turned to the "RUN" position, then the inertia switch circuit is ok.
The Pink/Black wire starts from the fuel pump relay and goes two directions. One side goes back to the fuel pump. The other side is the fuel pump monitor circuit and goes to pin #8 at the ECU. This wire should only be hot for a second or two when the ignition is turned to the RUN position.
The fuel pump relay receives power on the Black/yellow wire. It comes from a fusible link at the power distribution center. This wire should be hot at all times.
If all the above is working as designed, them you probably have a bad fuel pump.
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