fuel pump control module ?

[ahardb0dy]

94 Q45 T I've read that the fuel pump runs at 3 speeds, what determines which speed it runs at? Is it possible the fuel pump is running at a speed other than the one it's supposed to causing the lack of power my car feels like it has?

[maxnix]

i believe when the FPCU fails, it open circuits the ground leg and it fails to run period. Going directly to ground will cause it to run at top speed and die sooner.

[Q45tech]

The fuel pump is supplied with +12 [battery] thru the fuel pump fuse and the on/off relay. The FP ground terminal goes to FPCU where it passes thru Transistors which act like a big [high wattage] three position resistor.

The usual fast way to check is to T tap the fuel line feeding the injector rail and measure the psi under idle, cruise, and WOT all the way to redline while driving [gauge taped to windshield].

Usually it is the FP itself that turns low rpms because of commutator wear/corrosion and not the FPCU which fails to switch into least resistance mode for acceleration.

The high and medium resistance modes usually fail first [most stressed] from higher than design currents from the pump turning so slow.........thus the typical no crank situation.

The WOT acceleration or at least half throttle mode is rarely used so less stressed [from heat since it typically last less than 15 seconds] vs the idle/cruise mode is continuous......slow burn and failure after years and years if the pump is not replaced when it slows down. [makes noise].

I always keep a spare FPCU and jumper clips in trunk as I changed pumps at 140k and 220k [84k on current pump].............I also replaced controller at 220k after some weird engine cut offs finally no crank situation.

Just part of prorated $3k [$2400 in 94-95] in annual expense.

The FSM explains shows where what voltage ECU supplies FPCU for each mode.

However we care about fuel psi which is result.........this way you can blip throttle to check regulator and damper at the same time

[ahardb0dy]

I took the car for a drive today (first time driving the car) with the FPCM connected, leaving my subdivision I checked to see if I could powerbrake the car (which it normally won't do), I was able to easily break the tires loose, going down the road the car took it's time to get up to speed as it normally does.

I went down a deserted street nearby and pulled over, I unplugged the FPCM and hooked the terminal to ground and started to drive home, at first take off the car acted normally but once it started rolling it felt like a different car, RPM's climbed fast and steady, and once it shifted into high gear and I hit the gas it downshifted quick and smooth, no problems getting home and car ran like I think it should.

Could this mean that the car is not getting enough gas when the FPCM is connected but unplugging the FPCM and letting the fuel pump run at high speed allowed it to get all the gas it needed which in turn caused it to run better?

Would running the fuel pump at the high speed when taking off from a stop cause to much fuel to get to the engine thereby loading it up? And if it was loading up would that cause it to still run like crap from a stop?

Thanks

[DrewQ45]

If you end up needing one...I have a control module from a 92' for sale.

60+ ship.

[Q451990]

The fuel pressure regulator should prevent too much fuel pressure by opening and sending the excess fuel back to the tank via the return line. I don't know if it's as accurate as the tri-mode controled system though... probably not. Do you know how many miles are on your fuel pump? If it's more than 80K I would think about replacing it as preventative maintenence.

Heath

[Q45tech]

All 4 regulators [FP blow off valve, FPCU, Pressure pulse damper, and returnline regulator] need to work together properly. You will see this if you bother to test the rail input pressure under all conditions.

Work of art in maintaing 43.4 psi once the plenum pressure changes[acceleration mode] as the flow per minute increases 10 x [from rpm] and 9 x from duty cycle [inj open time] and an additional 13% from pressure rise from idle cruise 34 psi > 43.4 psi [WOT].

From idle to wot max rpm the flow amount per mintue changes 60 times ............from 4 HP at idle to overcome internal friction to 330 HP [the fuel equivalent------extra rich for cooling].

[ahardb0dy]

pulled the FPCM out saturday, re-soldered the burnt looking pin to the circuit board and added the wire that I've seen others do to theirs, nothing else looked damaged but can't tell just by looking at the components on the board. The module in this car looked different than the one's I've seen pictures of on this site as this one had 2 what looked like capacitors on the board next to each other.

[ahardb0dy]

no idea if this fuel pump is original or not, the car has 163K miles on it now, ever since the night it stalled on my wife it hasn't happened again, (yet!) I did do the wire suggestion to bypass the FPCM, for now I used a scotchlock connector on the wire and on the other end it has a clip, but I'm going to do as someone suggested and install a switch, will be easier on the wife if she has to do it herself.

[Q451990]

If the FPCU had burnt marks, and the pump is humming... you can bet it needs to be replaced. The burnt marks could be from a prior bad pump, but I wouldn't count on it.

Heath