It has been known for a long time that the stock Mazda FD fuel pump wiring does not

allow full voltage to reach the pump even after the FP resistor has been bypassed by

the relay. Many have totally rewired their FP by running full voltage directly from

the battery all the time. This works great except the FP runs full voltage even when

not needed. I decided to analyze and mod it for the easiest fix. This will help any

pump running the stock wiring to perform better.



Following is the results for my March 1992 RX-7 R1.



At idle with the FP resistor manually bypassed, the voltage at the battery was 14.2VDC.

Across the FP (+ wire to ground wire at the FP connector), it read 11.8VDC. That is a

2.4 volts loss, or 16.9%.



First I grounded the ground wire at the FP directly to the trunk floor. This had an

immediate result as the voltage across the pump went up by .4volts to 12.2VDC. That

is a 3.4% increase.



Next I ran a secondary + wire from the FP to the FP speed control relay. It was

initially disappointing as it made no difference at all. Later it did.



Looking at the wiring diagram for our car, The injectors (and some other functions)

get their power directly from the + side of the battery. The EGI relay which is

controlled by the ignition switch makes that connection. The ignition switch also

switches on the FP relay to allow power to the FP. But the FP gets it's power through

the ignition switch, not directly from the battery. This is where the major voltage

loss is.



I bought a 20amp-12VDC blade fuse holder from NAPA and some spare 20amp fuses. I cut

the BLUE solid + side wire between the FP relay and it's normal 20amp fuse which goes

to the ignition switch. I did this under the relay/fuse box on the driver's side fender.

I ran a heavy gage wire from the relay side of the cut through the new 20amp fuse to

the + side of the battery.



Retesting the idle voltage at the pump, it now was 13.5VDC. That is a 14.4% increase

in voltage to the pump over stock. Or a loss of only 4.9% as compared to 16.9% originally.

Remember the second wire which did not make any difference above. Well when I now

disconnected it, the FP voltage dropped by .4VDC to 13.1VDC, so it ends up helping after all.



What does all this mean. My pump will now be able to run closer to it's advertised potential

and pump more fuel at high boost levels. This will reduce the injector duty cycle.