Fuel pump keeps priming

So it was with respect to the replacement part as suspected. Will keep that in mind. Apparently Ford is sinking the motor rather than sourcing it which explains the PWM control signal table I was looking at in the tech manual. The pump used in other applications is likely sourced.

I actually had made a post about this.
Walbro 400lph added that stupid ground that messed it up.
At the same time we did the pump we did the s&h power upgrade we thought that had fail, so we reverted back to stock power.
I finally told the tech, hey let's look at the pump and see wassup!
Walbro refuse to accept the fact they wired this pump wrong. -_-
Now the check valve failed, so I started rebuilding them myself.
Better hose, better wiring and using a JDM 480 pump.
Drop duty from 88%(0.44) to 72% about. (making 438hp/438tq)

Oh man that mustve been hell to diagnose if you messed with the wiring at the same time. At least I know something was up with the new pumps because I didnt touch anything else.

But you still sorta assume that Bosch or Walbro get that shit right. At least after 10 years! If this was a new pump for a 2018, it would leave room for a designflaw to learn from.

redfirepearlgt said:

So it was with respect to the replacement part as suspected. Will keep that in mind. Apparently Ford is sinking the motor rather than sourcing it which explains the PWM control signal table I was looking at in the tech manual. The pump used in other applications is likely sourced.

Click to expand...

Just to be clear on this.
'Sinking' means that you have a constant +14Vdc on one input to the electric motor pump. To turn the pump on, you are applying a ground to the other input.

'Sourcing' means you have solid /constant ground on one side of the motor...and to turn it on.... you apply +14 vdc.

Same terminology used on other items... like relay coils etc.

PWM (pulse width modulation) is a method to increase / decrease electric motor speed /rpm by pulsing the full 14 vdc on /off. With PWM, you can tweak the 'on' time of each pulse....and also tweak the 'off' time for each pulse. In essence, what pwm does is alter the duty cycle on the motor. The advantage is....you can then lower the speed / rpm of the electric motor...without losing a ton of TQ.

If instead you just reduced the voltage to the electric motor, sure the speed will drop, but the tq will drop through the floor. As noted, the FPDC indicated on the obd port is, (for whatever reason) exactly one half of what it really is. IE: '44' = 88% FPDC. '50' = 100% FPDC.
'20' = 40%, etc, etc. With key on, eng OFF, Fuel rail pressure is 50 psi. With eng ON, rail pressure drops to 40 psi..and stays at 40 psi, whether at idle or redline..with or without blower on.

On a side note, I ran 10 gauge wire directly from battery terminal to trunk. FPDC dropped 10%..( down to 79-80% in my case). Oem wire is ( If I remember correctly) only 16 gauge. The bigger gauge wire has less of a V drop under load...so the pump gets a bit more voltage. If the FPDC is still too high, then the BAP goes in..which is just an unregulated DC to regulated DC converter..and they typ put out +17 vdc, regardless of load.

Dual GT-500 pumps work pretty good. IF FPDC still too high, then a dual BAP can be used...which sucks aprx 40A off the battery... at redline.

A few years back, my eng would gag... but only when I tried to get into boost, even feathering the throttle, for 2 psi boost. It would not go into boost. It would gag, and rail pressure dropped from 40 psi...down to 5-6 psi. Problem was the clogged 'sock' filter that goes over the bottom of the oem fuel pump. Once the sock was cleaned out, everything back to normal.