Destructive-

Which of the two black wires is the ground for the fuel pump on an obd2 gsr. 1999?

Both are black with white stripe, the thicker one has single silver dots, and thethinner has double silver dots on it.

I'm asking because I attempted the fuel pump rewire with the relay and the fuel pump isn't primig. At the same time I swapped my walbro to the new DW300, so I don't know if it's the wiring, or the pump itself.

I went 10gauge ( fused ) to 30 on relay, 10 gauge from 87 to pump, original pump 12v to 86 on relay, and for ground I cut the thicker black wire, tool the fuel pump side, soldered it to a wire coming from 85 on relay, and grounded them both to chassis. The remaining black wire that was cut was taped off.

So which one is the right black wire I'm looking for, the thick or thinner one? Or was I not supposed to cut the black at all?

NVturbo

Use a multimeter to see if one or both of the black/white wires ohms out. Touch one of the tester leads to a bolted bolt and the other lead to one of the wires. If your meter shows 0.00 and beeps, that wire is ground. If it shows a value (24.6 for example), then it is not ground.

Destructive-

I tried that and like 4 wires go to 0.00. Including the thick AND thin wire, along with a thin green one and another I believe.

I'm stumped.

Destructive-

Cmon guys I know you big HP cars have done the fuel pump rewire.

What did you guys do for the ground wire? Did you just ground off te relay and leave the fuel pump ground alone? Or did you ground off the pump along with te relay to the chassis?

fcm

Are you talking about the wires at the PGM-FI Main Relay or the wires at the fuel pump plug???

Both black/white leads at fuel pump/sending unit leads are grounds one for the pump the other for the thermistor, [low fuel indicator "unit"] and fuel gauge sending unit and the other for fuel pump, my guess would be the thicker one or the one that is the same gauge as the fuel pump power lead is the fuel pump ground.

I would not have cut the black leads at all, the relay should just be grounded to the cars chassis.

Why was the fuel pumps power lead rewired in the first place??? 94

wrx-killer-Sti-eater

iTrader: (1)

On our shop race car, I run 8 gauge from the battery to the boost pump. Between the boost pump and and the a1000 I have a bosh relay to control the pump. Also a main kill to kill everything in the car to complie with nhra and the class we run in. I don't use any factory grounds. Reason one because its shared between multi componets. And its just to thin. The pump really comes alive like this and you will be rewarded with extra pressure.

On my street car I am building. I will be running the new detricks drop in pumps or the new areomotive pumps and will be getting rid of my dual walbro setup. I will be keeping the full blown setup with the new pumps. The way my car is wired is 4 gauge straight to the pump. Pumps wired parrell, Relay between the power side of the pump.

4 gauge 12 volts-87
fuel pumps-30
fuel pump grounded to chassie
factory fuel pump wire 12 volt-85
relay ground side (86) to ground

This way the factory wiring controls my fuel pump and all I have to do is just turn the key and go.

You will hear and see a big difference if you run power straight from the battery to the pump. I seen and experiance the walbro pick up 5- 10 psi from doing this.

Destructive-

Is it ok if I reversed 30 and 87? The way I did it was:

Battery 10gauge - 30
Original f.p wire to pump - 87
Original f.p wire from harness - 86
Relay ground - 85

It wouldn't prime though, so I took everything off and soldered the fp wire back together and it turned on again. I'm confused. A 30 min project turned into an 11 hour nightmare

fcm

Reversing #30 and #87 will not make a diff., the only advantage of using #87 as the 12V input is that you could then ground #87a so when relay is not energized, [off] the power lead going to pump, [#30] is a ground, [another security layer, preventing a bypass of the relay if it is used as a "kill".

If the rewire, [relay install] is not being used as a security layer, as yours is not, the ground to #87 is pointless and it makes absolutely no diff. if #30 and #87 are reversed.

Sound so me like either the relay is bad or the #85 is not grounded. 94

PS, Jeezzz Killer, 4ga, how much current do your fuel pumps need????
Definitely not 150A LOL, 12ga has a capacity of 40A, assuming you are using standard 30/40 amp SPDT or SPST relays anything thicker is redundant, yes/no, or is it just you like to over-Killer?

Destructive-

Ok what the hell am I doing wrong?

I went from the battery to #30 on the relay. I cut the original 12v wire to the fuel pump, connected the side that goes to the pump to #87 on relay, connected the side of original 12v that goes into harness to #86 on relay. And ran a ground from #85 relay to chassis and left the pump to ground off the harness. The fuel pump wouldn't prime or run like that...

wrx-killer-Sti-eater

iTrader: (1)

Do you have a multi meter? This will tell us whats wrong. Bad relay? Or is there a fuse on the battery lead that should be before the fire wall if the battery is in the engine bay that might be popped? The meter will tell us were power is coming and not coming. Please get one.

Destructive-

i have a multimeter, i checked the wires already, i have a 30 amp in line fuse from the battery to the relay (on the 10 gauge wire) , i believe the relay is a 40amp.

when i turn the key over, i have power for 2 seconds at #87 (to fuel pump) . So thats why im so confused. theoretically, everything is working. but when i connect the pump, and try to start it, it doesnt prime

Destructive-

as far as "ground" on relay, does it mean run a ground from relay to chassis, leaving the ground on fuel pump untouched (fuel pump still grounding from oem wiring) ?

or does it mean cut original ground from fuel pump, and ground the pump along with relay into chassis?

wrx-killer-Sti-eater

iTrader: (1)

The relay needs its own ground to operate. So ground the relay 85 or 86 post. If there is 12 volts on either one. The opposite needs a ground for the relay to work.

As far as the pump. Either leave it to the factory ground. Or re ground it to the chassie.

fcm

So the relay you installed is working, "i have power for 2 seconds at #87", meaning the lead you connected to #86, [fuel pump power lead, PGM-FI Main Relay side] and the ground to #85 are all correct and working, sounds to me like fuel pump is the problem.

Try supplying power directly to the fuel pump power lead, directly from you 10ga lead, to see if pump works. 94

Destructive-

I did, and the pump works. I removed all the wiring I added and put everything back to original, and the car is now running, but I need that fuel pump rewire :/. Another thing that was suggested is that everything must be done on the harness side of the plug, not the fuel pump side of the plug. I did it on the fuel pump side. Would that cause it?

Another thing I guess I should add is that I have a (simple) fuel cut off switch on the harness side of the plug. I interrupted the 12v wire, and someone suggested I should interrupt the ground wire instead because that switch is causing resistance, is that true?

Edit - and yes I made sure the switch was to ON haha

wrx-killer-Sti-eater

iTrader: (1)

I thinking broken switch or bad relay. Call me tommorrow and I can walk you threw it. Or post here and fcm or I will continue to try to figure this out.

fcm

Resistance is resistance, it will be there if it is on a power lead or a ground lead.

The recommendation to install the kill switch on the ground, probably means the PGM-FI Main Relay ground, there are three good reasons for doing so, first it is a ground, [your not messing with 12V+, the PGM-FI Main Relay ground is low current, [less then 250mA] requiring a very small, easily hidden 1A switch, and lastly, no ground to the PGM-FI Main Relay "kills" the fuel pump, the fuel injectors, the ECU/ECM and a few engine valve/solenoids.

Again, why are you installing a relay on the fuel pump power line?

I can almost understand if you have a HO fuel pump and ran 10ga all the way to the pump, but as you say you connected the stock fuel pump power lead to the relays output #87 and although it is OK to use the stock lead for relay control, [#86] using the stock lead as power to the fuel pump has made the 10ga pointless, essentially you have done nothing but use a relay, [PGM-FI Main Relay] to control another relay, you can not supply any more current to the fuel pump then the stock fuel pump power lead can supply. 94

Destructive-

It's done to provide constant 12v to the pump as the stock fuel pump 12v is so small it loses power by the time it gets to the pump. Providing a lead straight from the battery provides a true 12v constantly, waking the pump up.

fcm

I understand that, but if you are using the stock power lead from the relay you installed to the fuel pump the 10ga to the relay will make no diff. the stock lead can not supply any more current, current is limited by the gauge of the lead, so if you still have the stock lead, no more current can be supplied.

Also the 30A fuse is far to big for the fuel pump and the stock power lead, if something goes wrong you will have a fire, the stock power lead will burn almost instantly. 94

Destructive-

Oh snaps! Ok, should I use a 15amp instead?

wrx-killer-Sti-eater

iTrader: (1)

Fcm, I think he trying to say is that he using the factory fuel pump wire to control the relay to send battery voltage straight to the pump. So the main relay can still control it like it was stock.

Destructive-

actually i believe fcm has the right description. when i cut the original 12v lead to fuel pump, i used the harness side to power the new relay, BUT i left the fuel pump side original 12v alone and just connected it to 87.

so fcm, instead, should i use the harness side original 12v to power relay, and completely replace the fuel pump side to 10 gauge? essentially running 10 gauge all the way to the pump? so... 10 gauge from battery to relay, and 10 gauge from relay to fuel pump?

this WOULD make sense, although from all the fuel pump rewires i have never read to do this. it'd be great if someone who knows about the fuel pump rewire came in and posted ~_~

Destructive-

ok so i searched and found another thread here on H-T. and stole this post from "White Smoke" so, per this post, fcm i believe you are correct

fcm

That would be correct^^^, but do not install a bigger fuse then the stock fuse anyway, [7.5A I think]. 94

Destructive-

ok so i will be attempting this again friday after work. and im going to be doing a how-to along the way for other people for the future. haha.
ill keep you guys updated