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Fuel Pump Rewire -(Write up & Data)

11100 Views 20 Replies 8 Participants Last post by  Nismo91ser
Been planning on trying this for sometime, finally got around to it tonight, so here it goes. I have a '91 B-13 SE-R with a Walbro 255, and also a trunk mounted battery. I used a 30 amp relay and harness from an off-road light kit, which had 12 guage wiring. I used what I believe is a ignition coil connector, (factory B-13, looks like 14 guage wire) that was cut from a engine harness. I soldered the new connector to the harness that was attached to the relay. The new connector fits the factory connector on the fuel tank perfectly, even locks in place. Power for the relay was taken directly from the battery, factory fuel pump wiring triggers the relay. All data provided by an OTC 300 digital multimeter with 200 amp current clamp. Battery voltage taken at battery,(duh!) and the pump voltage was taken by backprobing FP connector at tank. Fuel pressure is at idle, vacuum connected.

Before Rewire:
Battery Voltage Car off, ignition on: 12.7v
Fuel Pump Voltage-Prime: 10.29v @ 7.7 amp draw

Battery Voltage Run:13.9v
Fuel Pump Voltage-Run: 12.08v @ 6.9 amp draw
Fuel Pressure: 48 psi

After Rewire:
Battery Voltage Car off, ignition on: 12.5v
Fuel pump Voltage-Prime: 12.02v @ 7.0 amp draw :D

Battery Voltage Run: 14.1v
Fuel pump voltage-Run: 14.0v @ 7.0 amp draw :D
Fuel pressure: 56 psi :eek:

Not bad for about 45 minutes of work, I would imagine it helps more for those with trunk mounted batteries, because the power wire to the pump is only about 1 foot long. Anyways that's my $.02.

Travis E.
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Excellent findings, Travis. Tell me this: Did the fuel pump audibly appear to be working harder? Could you tell it was getting more juice?
If anything I would say it was quieter, it seemed the pitch changed somewhat. It "sounded" faster , but that could be just in my head.

Travis E.

PS Sorry about posting this in the General forum......
Awesome...............this is nice for us turbo guys using stock fuel pumps.
Heres goes a excellant write up on how to do this mod.

http://www.stealth316.com/2-fuelpump-rewire.htm

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a 30 amp fuse?! the stocker is 15amp.
Dont use the colors on that schematic, as they may not be correct. Just letting people know, so they don't jump to conclusions. It's a great basic write up though.
Before Rewire:
Battery Voltage Car off, ignition on: 12.13v
Fuel Pump Voltage-Prime: 10.54v

Battery Voltage Running: 14.30v
Fuel Pump Voltage-Run: 12.76

*My battery is relocated to trunk

to be continued with after re-wire results

One more thing to be noted there is a 2.65 volt drop at the negative wire on the fuel pump hence the 12.76 volts at the fuel pump power wire.
Still haven;t rewired yet but I found out why I had some much resistance on the negative wire, turns out the fuel pump relay was going out and today it died, symptoms where car would die after start up and finally would not start anymore, so I inspected the realy and shook it and it sounded like lil rock where inside of it. Replaced with a new used one I had and everything is back to normal and the resistance in teh negative wire went down from 2.65v to .017v
charlie2020 said:
Before Rewire:
Battery Voltage Car off, ignition on: 12.13v
Fuel Pump Voltage-Prime: 10.54v

Battery Voltage Running: 14.30v
Fuel Pump Voltage-Run: 12.76

*My battery is relocated to trunk

to be continued with after re-wire results

One more thing to be noted there is a 2.65 volt drop at the negative wire on the fuel pump hence the 12.76 volts at the fuel pump power wire.
Well I finally rewired it and I got one word..........AWESOME!!!

Fuel Pump Voltage-Run is now 14.00v and my car feels like it gained around 15whp it is so ****in smooth..........now I know I gotta get me a WALBRO for sure now.
i have my batt in the engine bay...but i also have 4gauge wire going to the rear for my stereo, which is also connected to a cap. Could i just run the power wire front the batt side of the cap???since that side has no real draw from the amp???? I got everythig else to do the job just wondering if i could do that. thanks Tom
also do i need a adj. FPR since the FP will be higher???
Nismo91ser said:
i have my batt in the engine bay...but i also have 4gauge wire going to the rear for my stereo, which is also connected to a cap. Could i just run the power wire front the batt side of the cap???since that side has no real draw from the amp???? I got everythig else to do the job just wondering if i could do that. thanks Tom
u just read my mind
If you are running stock pump and FPR then no. The reason my pressure changed so much was I have the Walbro and Nismo FPR. The stock regulator would keep it at stock pressure. If you can check your voltages like Charlie and I did, you can see how much it will help. I would imagine it helps the guys with batteries relocated to the trunk more, since you almost double the distance the current travels.

Travis E.
well im running a walboro and a stock fpr and im going to try it out so that everyones questions can be answered prob. tues or wed. I'll let anyone know
well i just did the re-wire too.....

before- 12 volts at idle
after -14volts and the pump is not as loud.

FP-with vac off is like 48 and with hose on is like 38

also that diagram is wrong

correct terminal location
30-B+
85-ground
86-b/r stripe(92 classic) harness side
87-b/r stripe(92 classic) pump side
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Nismo91ser said:
well i just did the re-wire too.....

before- 12 volts at idle
after -14volts and the pump is not as loud.

FP-with vac off is like 48 and with hose on is like 38

also that diagram is wrong

correct terminal location
30-B+
85-ground
86-b/r stripe(92 classic) harness side
87-b/r stripe(92 classic) pump side
Was that with the stock fuel pump and fpr?
Ttt Ttt
charlie2020 said:
Was that with the stock fuel pump and fpr?
nope that was a walbro 255, check the first post, first parargraph. i beleive it was a stock fpr tho, with a gauge in-line.
I quoted Nismo91ser not skyliner
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