fuel pump runs after engine off

[shane1230]

Mercruiser 4.3L MPI S/N 0M357557 .
Fuel pump randomly runs after engine shut down. At key turn on fuel pump turns on for 2-3 seconds then shuts down. Engine starting takes 4-5 seconds of key turn. However sometimes after running the boat the pump will stay on after the key is off. I checked fuel pressure at fuel rail behind the throttle body while on the trailer in driveway. Pressure after three second pump turn off is 36psi while idling in neutral after start is around 30psi.
Will replacing the fuel pump fix my slow start and continuing run after key turn off?

 

[alldodge]

The fuel pump is turned ON after the Main Power Relay (MPR) is energized and then the ECM applies a ground to the Fuel Pump Relay (FPR). For the fuel pump to stay ON, both MPR and FPR needs to be energized, or there needs to have another power source to the fuel pump

Fuel pressure when running should be 43 psi

Could be your key switch is going bad

Place a voltmeter on the purple wire on the key switch and see if you can get it to saty hot when key is turned OFF. No need to start the motor, just flip the key back n forth

The fuel pressure is controlled by the pump and the regulator

Will replacing the fuel pump fix my ......... continuing run after key turn off?

No

 

[shane1230]

Thanks for the quick reply. I will indeed check the voltage at the key switch over the next few days and report back.

 

[shane1230]

The fuel pump is turned ON after the Main Power Relay (MPR) is energized and then the ECM applies a ground to the Fuel Pump Relay (FPR). For the fuel pump to stay ON, both MPR and FPR needs to be energized, or there needs to have another power source to the fuel pump

Fuel pressure when running should be 43 psi

Could be your key switch is going bad

Place a voltmeter on the purple wire on the key switch and see if you can get it to saty hot when key is turned OFF. No need to start the motor, just flip the key back n forth

The fuel pressure is controlled by the pump and the regulator



No

Finally able to test key switch. Switch test good, no power at purple wire when switch is in off position. Fuel pump continues to run once engine is started and engine is turned off. I have to disconnect power at the battery (master battery switch) to make fuel pump turn off.

Any thoughts for other things that could cause this issue?

 

[alldodge]

Could be the MPR is staying turned ON. If MPR turned OFF there would be no power to the FPR

Find out which relay clicks when key is turned ON. This should be the MPR. Might have to remove one to find the right one if they both click at the same time (which they should not)

The MPR will also have a red/purple wire feeding it

You can get these relays at the local auto store