Fuel pump ground?

[elwesso]

so as some may know, I worked on a members car and much to my chagrin the fuel pump controller (or so I think) went out..

Quick history.. I replaced the fuel pump (new OEM), and about 50 miles later the car died.. Fuel pump was not running, so I grounded the white wire on the control unit, the car starts right up...

So I had him get a new fuel pump controller, he plugs it in and still doesnt work..

Ive heard of the actual ground for the fuel pump going bad (one case) when a fuel pump controller replacement did not do the trick.. Or rather, re-grounding either the fuel pump controller or whatever controls the ground causes the fuel pump to fire back up...

I know the fuel pump relay is kicking on and off when its supposed to...

Where does the fuel pump controller get its ground?? Does it ground through the case? I looked at the FSM I dont see any definite place where the ground comes in (EFEC-150 in the 1994 FSM)

[3Q Jay]

yes, thru the case. the white wire from the pump is ground, and it goes directly to the white wire on the fpcu, which in turn gets connected to chassis by the fpcu circuitry. the reason why when you ground the white wire directly to the frame that the pump runs full blast is that you are bypasisng the 'step down' circuitry of the FPCU grounding path.

by new, i'm guessing you mean used but new to the situation FPCU? how do we know it is good?

[Infinitiguy19]

Wes see pages EL-249,EL-275 in the 1994 Q45 FSM.

I won't say anything.

Just kidding.

And like 3QJay said: The Board tells it all, Like they say on Pass time: The burnout tells it all. Or like I say: The mother tells it all (About the daughter).

[elwesso]

ok so essentially, if I ran a new ground from the case to some better body ground that should rule that out, yes?

Thanks, we'll give that a try.

[Q45tech]

It is always interesting to measure the current draw with a direct ground and then thru FOCU. You will see that even in WOT MODE the FPCU limits current and thus speed to 90% of max this adds significant reliability and life to the pump compared to running direct.

The Q45 pump is rated at 241 liters per hour at 43.4 psi WITH 13.5 volts.As far as I know no PUBLISHED data has been taken at the lower rpm and lower pressure. Other than the potential flow increases slightly to 249.6 LPH at 35 psi with 13.5 volts.

SINCE MOST are interested in PEAK FLOW not peak reliability at the lower average pump rpm.

http://www.wmea.net/Technical%...8.pdf

"....................Evidence suggests that wear rates were most reduced at those rotor speeds where surface waves on the wavy rotor passing beneath the brush caused the brush-stiffness-rotor system to resonate. Studies of contact voltage drop suggest that under these resonant conditions, the brush and rotor stayed connected. Also, no evidence of arcing or micro-arcing was found on the copper track. This study shows appreciable reductions (up to 50%) in wear rate possible on brush rotor systems by prescribing tiny surface waves on the rotor and running the rotor at speeds such that the surface waves induce microvibrations and resonance..................http://ieeexplore.ieee.org/xpl...=8847

http://www.stealth316.com/misc/fuelpump ... nteresting that pump draws 7.4 amperes at 13.5 volts at 35 psivs 7.9 amperes at 13.5 volts at 45 psi