Fuel pump wiring
Definately use a fuel pump relay. #10 red wire from the alternator stud to the relay for power. Fuse this wire near the alternator end. Relay is triggered by the computer.
And if I recall correctly, the PCM provides a switched 12V to pull the relay. Unlike the fan relays, where the PCM switches ground.
So the relay will have:
10ga 12VDC in from fused battery source
10ga 12VDC out to fuel pump
14ga (?) 12VDC in from PCM
14ga (?) to chassis ground
So the relay will have:
10ga 12VDC in from fused battery source
10ga 12VDC out to fuel pump
14ga (?) 12VDC in from PCM
14ga (?) to chassis ground
Fuel Pump Relay Amperage? And if I recall correctly, the PCM provides a switched 12V to pull the relay. Unlike the fan relays, where the PCM switches ground.
So the relay will have:
10ga 12VDC in from fused battery source
10ga 12VDC out to fuel pump
14ga (?) 12VDC in from PCM
14ga (?) to chassis ground
So the relay will have:
10ga 12VDC in from fused battery source
10ga 12VDC out to fuel pump
14ga (?) 12VDC in from PCM
14ga (?) to chassis ground
A standard 30 amp BOSCH square style relay works fine for one pump. It would wire as follows:
pin 30 - fused power in
pin 87 - output to pump
pin 85 - ground
pin 86 - + from ECM that turns on pump
pin 30 - fused power in
pin 87 - output to pump
pin 85 - ground
pin 86 - + from ECM that turns on pump
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TECH Resident
Joined: May 2004
Posts: 792
Likes: 2
From: SoCal
I've got the Walbro #GSL392, and the Walbro chart shows that it draws 13.9 AMPs. Why would you need a #10 wire?
"and remember, PCm will only send a three second 12v power until the engine is running." Once the engine is running, is there no longer 12V power to signal the relay? If this is indeed the case, does the relay need to be the latching type or how do you manage to keep the fuel pump running?
"Which raises a question. In an accident, would this be safe? "
This question keeps comming up in my mind as well. Many of the Cobra replica builders that run the Ford EFI, also install the Ford inertia switch that cuts the power to the fuel pump relay in case of an accident or roll-over. Do GM cars have some type of similar device?
Thank,
Andy1
"and remember, PCm will only send a three second 12v power until the engine is running." Once the engine is running, is there no longer 12V power to signal the relay? If this is indeed the case, does the relay need to be the latching type or how do you manage to keep the fuel pump running?
"Which raises a question. In an accident, would this be safe? "
This question keeps comming up in my mind as well. Many of the Cobra replica builders that run the Ford EFI, also install the Ford inertia switch that cuts the power to the fuel pump relay in case of an accident or roll-over. Do GM cars have some type of similar device?
Thank,
Andy1
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Verdad Gallardo You don't really need a #10 gauge size wire. You could use a #14 gauge wire or a #12. Its just that its a bit of a long run & I prefer #10 wire. And planning for future pump(s) size upgrades does'nt hurt.
what all does the power output fromt he PCM do? im redoing my fuelpump wiring as i wired in my inertia switch and CCRM frm my 94 mustang and i keep having fuel pump connectivity problems. im sure its my CCRM but i plan to wire it straight to an ignition source in my trunk. when my key is on....i want my fuel pump on. i personally dont feel the PCM does anything as far as read outputs for tuning or anything fancy. isnt it strickly just an on offf switch for the pump? the whole idea is not to run a wire from the rear all the way to the bay.
thanks, adam
thanks, adam
Staging Lane
Joined: Oct 2006
Posts: 62
Likes: 0
The PCM can't give the required current to power a pump, just a relay coil which uses considerably less current. So you use the PCM to energise the relay coil which in turn connects the battery (= lots of current) to the pump via the relay contacts.
The benefit of the relay is it takes the load off of your ignition switch, if you have it wired up to come on whenever the key is on. The iginition switch isn't designed to handle the kind of amps an electric fuel pump pulls.
Hard-wire your fuel pump to a manual switch, and Darwin may have a chat with you later on.
can anyone verify this? this was my question about wiring up the pump straight to an ignition source. fbodys dont have an inertia switch or anything that i would see killing the pump. how does the pcm know the car was in an accident? also, you have to remember most cars making serious power go with a stand alone which doesnt have any type of fuel cutoff for accidents.
My 140 gph pump has a 7.5 amp fuse. 10 guage wire won't hurt anything but it is massive overkill.
Sure there are some wrecks that will leave the engine turning, but if the fuel supply line is severed guess what...the engine stops. See above.
Rig the fuel pump on a manual switch, and even with the engine stopped and a fuel line ruptured you'll still be spraying gas as long as the battery and FP circuit are intact.
They also have fire suppression systems. Don't look at what teenagers and 20-somethings are driving, look at what the guys with a few gray hairs run. There's a reason they're still alive and driving.
I have a carb, but used a relay and an oil pressure cut off switch. The relay lets me run thinner wire to the oil pressure switch. And like someone said takes the load off the ignition switch. I have it fused right off the main circuit.
My 140 gph pump has a 7.5 amp fuse. 10 guage wire won't hurt anything but it is massive overkill.
My 140 gph pump has a 7.5 amp fuse. 10 guage wire won't hurt anything but it is massive overkill.
Does this eliminate the need for "Hotwire" kits you see for cars that were EFI from the factory (F-bodies, Turbo Buicks, etc)? I know the factory wiring was marginal and the "Hotwire" kits were the way to ensure a full 13.2v (IIRC) to the pump.