F A S S Fuel Pump

[Speedy]

F A S S fuel pump does not " Salute " when the key is first powered up. this is an intermittent problem.
If I bump the key 1 or 2 times, the pump will run for the 30second interval. truck only starts when the pump is running. any thoughts?

 

[petersonj]

The lift pump only runs for only 1/4 second (from the FSM) when key is switched to "On" position. If the key is switched back to "Off" and then back to "On" right away, the pump will likely not run. The ECM needs time to reset. The same thing goes for the bump start.

truck only starts when the pump is running. any thoughts?

So, are you saying that the lift pump is not running while the engine is cranking and the engine won't start? Or, are you saying something else?

- John

 

[Speedy]

John, When I switch the key on, sometimes the pump will salute. the truck will start and run fine... If the pump does not salute the truck will not start. If I cycle the key and dump the start the pump will run for the 30second interval, and the truck will start and run fine

 

[SAndreasen]

My 99 sometimes does the same thing don’t know why but sometimes you have to bump the key to get the pump to run

 

[petersonj]

When I switch the key on, sometimes the pump will salute. the truck will start and run fine... If the pump does not salute the truck will not start. If I cycle the key and dump the start the pump will run for the 30second interval, and the truck will start and run fine

I am wondering if you are having a problem with the ignition switch. Fuse #9 in the Junction Block (fuse panel by the driver's door) receives power from the ignition switch start / run circuit. From fuse #9, power goes directly to the ECM. The ECM energizes the coil on the fuel pump relay for the VP44 and also energizes the lift pump. You could easily use a test lamp to see if power is intermittent at fuse #9.

- John

 

[AH64ID]

The FASS has a relay triggered by the ECM lift pump circuit, right?

If that relay is slow to close you would get the symptoms you’re describing since the ECM only briefly commands the pump at ignition cycling.