Okay, we all know about bumping the starter and having the fuel pump run for 20 seconds. All of a sudden mine stopped doing this. All it does is turn on & off very quickly, like 3-4 times in 2 seconds then stops.

What is going on with my FP? Is it my ECM?

What would cause this?

 

Perhaps the smarty is messing with normal programing.
Try walking away for five minutes with key in hand. try again.
Mine will quit sometimes if I repeat.

 

When I had my 2000 3500, that still has the original VP at 205,000 when I sold it, when the key was turned on to start, the pump (LP) would run for about a second and turn off. It did that for 9 years. I replaced the pump (LP)twice.

The computer suppositly, turns the voltage down to 9V when you start and they turns it back on 12V for continous operation or whatever is needed to keep the fuel flow up.

Best thing to do is put a guage on it and see if its putting out after you start.

Edit; I just saw you have a Fass system, so unless you still have your LP this really does not apply, but the power turn down from the ECM should, Sorry.

Dave

 

Thanks for the input.

I do have a FP gage and it drop to 5-10 PSI, and jumps around.

I wonder if the pump is getting weak and will not run on 9v?

 

I have a personal opinion about the LP situation with 2nd Generation Trucks witht he VP44 and LP.

Some trucks run forever on an LP and some can't get 25,000 miles out of one.
Its one of two things. Either the pump is being destroyed by debris in the tank as its pulled through the system (no filter prior to the pump) or the computer never turns the voltage back up causing the pump to run hot on low voltage.

I checked my 2000 with a meter and you can see the drop and 12V after start up. Alot of people that reposition their new pumps in a differant location than the LP forget to run a heavier gage wire. DC voltage is very subsetible to loss at a distance with small wire that causes the electric portion of the pump to labor.

Dave

 

Good points Dave.

The FASS HVLP pump I have uses the signal from the ECM to operate a 12v relay and then it sends a full 12v to the pump via pretty heavy wires.

 

340,000 miles with no upgrades and now doing a few, gotta love a 24V.

 

when you bump the starter...put pressure on the wires that connect to the lift pump...pull ...push...i did alot of trouble shooting till i found the wire was broken at the connection point and contact was intermittent. my fix was replacing the connector. they are sold on jeggs.com. best to disconnect the connector and place a voltage meter on it to see what kind of voltage you are getting while moving the wires around. when i pushed steady pressure i had 12 volts when i pulled on the connector i would have zero volts, hope this helps...