Upgrading fuel pump electrical

[A.J.]

This is the background that lead to me upgrading the electrical. You can skip this section and jump right to the write-up. I'm in the process of upgrading my fuel system for E85. I've heard you need 30%-50% more fuel. I was having trouble tuning my van for 91 octane at 25 psi of boost. Base fuel pressure (no vacuum at regulator) is 43 psi. At 15 psi/boost at WOT I should have 58 psi fuel pressure and only had 51 and at 25 psi/boost WOT I should have 68 psi of fuel pressure but I only had 40. I borrowed a friends 340 LPH to replace my 255 LPH (which I think is failing). Fuel pressure was better but I still didn't reach 68 psi of fuel pressure. I forgot to check voltage at the pump so I did. At idle I have 13.8v at the battery. At the fuel pump (pump side of the connector at the pump) I only had 12.3v, a 1.5v loss. On a road test at 15 psi of boost I had 11.95v. I had planned on running 10 gauge wire to the pump so I didn't bother trying to find where the voltage drop was. It's 26 year old wiring, I'm replacing it all.

So I want to run 10 gauge wire to the pump but what to do at top of the sending unit? I don't want to run 10 gauge just to have to reduce it at the sending unit to 14 gauge. I got a spare sending unit from a junk yard to experiment with.

Factory power wire to the fuel pump on the left, 12-14 gauge. Good enough for stock but not for what I want to do. 10 gauge wire that I'm upgrading to on the right.


This is the inside and outside of the fuel pump sending unit. You can see one of the terminals is kind of burnt.




Here is the electrical mount on the sending unit. On the inside I ground off the "roll over" to get it apart. There is an o-ring that seals it from fuel vapors from escaping. Good news for me.


The electrical terminal measures .125". 3mm is smaller, 4mm is bigger. I went with 4mm to keep the shoulder of the bolt to help seal the o-ring. The 3mm bolts didn't come with shoulders.


I cut new threads to the length I needed and then trimmed the bolt to the length I needed.


I got the o-rings from a kit I bought from Harbor Freight.


And finished. I also upgraded the lines to 3/8", pressure and return. I brazed them in. Just so every one knows who attempts this, you have to put the line through the sending unit before you start to bend them.


Next to the factory sending unit.

[cordes]

Wow, there won't be a significant voltage drop though that. Nice work AJ.

[zin]

Be sure the ground side is up to the same challenge, they'll give you more grief than almost anything else!

I can't see the pictures right now, but knowing your work/attitude, I'm sure it's top notch!

Mike

- - - Updated - - -

Be sure the ground side is up to the same challenge, they'll give you more grief than almost anything else!

I can't see the pictures right now, but knowing your work/attitude, I'm sure it's top notch!

Mike

[bgbmxer]

What's the other side look like? The pump side of the hanger and that wire?

i did similar with my lines but i brazed an weld fittings on.

[A.J.]

Be sure the ground side is up to the same challenge, they'll give you more grief than almost anything else!

I can't see the pictures right now, but knowing your work/attitude, I'm sure it's top notch!

Mike

You are correct about the ground. The burnt terminal on my factory sending unit was the ground. The ground was also burnt on a fuel pump that I replaced on my Dad's wagon. Grounds are frequently overlooked. For the ground I was going to run a 10 gauge wire all the way from the pump to the battery but that seemed like a waste of wire when the chassis is ground. So I decided to run two ground wires off of the top of my sending unit and ground them twelve inches apart from each other.

What's the other side look like? The pump side of the hanger and that wire?

i did similar with my lines but i brazed an weld fittings on.

[zin]

That's probably fine, but be sure the body/engine/battery are all well connected, the body isn't the best conductor, but it isn't like you've relocated the battery to the rear, so I'm sure you'll be fine.

As an aside, and so you can understand why I even worry about conductivity of the body work, many racecars (tube frame), have grounding issues even though the grounds are attached directly to the metal of the frame, this turns out to be due to the chrome-molly material not conducting very well.

Mike

- - - Updated - - -

That's probably fine, but be sure the body/engine/battery are all well connected, the body isn't the best conductor, but it isn't like you've relocated the battery to the rear, so I'm sure you'll be fine.

As an aside, and so you can understand why I even worry about conductivity of the body work, many racecars (tube frame), have grounding issues even though the grounds are attached directly to the metal of the frame, this turns out to be due to the chrome-molly material not conducting very well.

Mike

[iTurbo]

I'm also interested in running E85 eventually. Nice work! The electrical/wiring at the fuel pump sender is definitely a weak point in my experience.

About a year ago, I put a fuel pump upgrade on my brother's old Regal GS (S/C 3800). It consisted of replacing the stock fuel pump wiring with lower gauge wiring (#) and using the original fuel pump wiring as the 'turn-on' lead for a relay. Perhaps that is next? It was from Racetronix and I give it some credit for allowing me to run the 3.4" S/C pulley on 91 octane and running great as ever.

[A.J.]

That's probably fine, but be sure the body/engine/battery are all well connected, the body isn't the best conductor, but it isn't like you've relocated the battery to the rear, so I'm sure you'll be fine.

As an aside, and so you can understand why I even worry about conductivity of the body work, many racecars (tube frame), have grounding issues even though the grounds are attached directly to the metal of the frame, this turns out to be due to the chrome-molly material not conducting very well.

Mike

Next it running better battery to body grounds. I'm not satisfied with what I have now.

I'm also interested in running E85 eventually. Nice work! The electrical/wiring at the fuel pump sender is definitely a weak point in my experience.

About a year ago, I put a fuel pump upgrade on my brother's old Regal GS (S/C 3800). It consisted of replacing the stock fuel pump wiring with lower gauge wiring (#) and using the original fuel pump wiring as the 'turn-on' lead for a relay. Perhaps that is next? It was from Racetronix and I give it some credit for allowing me to run the 3.4" S/C pulley on 91 octane and running great as ever.

That's basically what I did. New 10 gauge wire to power the pump and a wire off the ASD relay to turn on another relay that powers the pump.

[Keito]

SRT 4 guys figured out the fuel pump rewire back in 07
Claimed it even helped MPG's
Unfortunately a few guys burned their cars to the ground which made people second guess the mod

http://www.srtforums.com/forums/f187...e-must-389383/

[A.J.]

SRT 4 guys figured out the fuel pump rewire back in 07
Claimed it even helped MPG's
Unfortunately a few guys burned their cars to the ground which made people second guess the mod

http://www.srtforums.com/forums/f187...e-must-389383/

SRT forums is where I got the idea. I decided to do my own write up because a lot of people can't tolerate the some of the knuckle heads over there. I just went through all 16 pages and there was nothing about anybody burning their cars to the ground. I can see it happening though if people don't put in any circuit protection. I have a fuse/relay box off of a '95 Caravan. I have the ASD relay power wire that sent power to the fuel pump power up the new fuel pump relay which draws it's power from a 30 amp fuse and then goes out to the pump. I have the fuel pump wire in it's own wire loom and zip tied to the frame.

[Tbird232ci]

Doing anything for weather protection?

I live in a salt state, so pretty much any electrical connection left to the weather corrodes away if driven year round.

[A.J.]

Doing anything for weather protection?

I live in a salt state, so pretty much any electrical connection left to the weather corrodes away if driven year round.

The fuse and relay are in a fuse box under the hood. The connectors in the back are shielded crimp connectors but I didn't use heat shrink to keep the elements out. Things don't corrode here.

[ShadowFromHell]

DSM guys have been doing this for years. Its a great idea. I will second the ground thing. Years ago I was big into car audio and had 2000w worth of amps in my Jeep. I had a big alt and still got dimming when the bass hit. I was going to add a capacitor but then found a article on upgrading grounds. Turned out while I had a 4 gauge ground from the amp to the body, I only has a 16 gauge from the battery to the body! So I bumped that up to a 4 gauge and EVERYTHING got better! The heater motor had more power, the headlights were brighter, the dimming was gone, and I think the winch even picked up a little power! Now, this was on a 1970 Jeep with horrid factory wiring, but just goes to show how much grounds affect things.

I should do this to my neon, with the old school Begi FMU I have some high fuel pressures, I bet a rewire would help a the pump out a lot.

Doing this mod with a relay also makes it easy to add a kill switch to stop thieves. I know we dont really have a problem with that, but it makes it really easy to add a hidden switch in between the factory fuel pump wiring and the relay. My buddies RX7 was setup like that when he bought it. Hopefully it makes the thief thing the car is broke because is should start if hotwired, and then quickly die.

[wallace]

Any results after the wiring upgrade? Is the 255 now up to the task?

[A.J.]

Yes. I checked voltage at the pump and it was .4 volts less than at the battery but that was before I hooked up more battery to chassis grounds. That was at idle, I didn't check it under boost which I know I should because that's when it's under load. I am not using the 255 lph pump anymore. I am now using a 340 lph pump because at some point I'm going to be running E85. I checked fuel pressure under boost and at 15 psi of boost I have 60 psi of fuel pressure and at 25 psi I have 70 psi of fuel pressure. So I'm getting sufficient pressure and volume now.

[wallace]

Good deal.

[csxtra]

Bumping this up to say thanks A.J. for posting this up. The fuel pump in my CSX just quit while idling in my driveway a couple of weeks ago.

I thought the Aeromotive Stealth 340 pump had died, but when I checked the connections, it turns out one of the pins on the hanger did not have good continuity.

So I duplicated your setup with the M4 bolts and now it is working great.

Many thanks for your writeup A.J.

[A.J.]

Bumping this up to say thanks A.J. for posting this up. The fuel pump in my CSX just quit while idling in my driveway a couple of weeks ago.

I thought the Aeromotive Stealth 340 pump had died, but when I checked the connections, it turns out one of the pins on the hanger did not have good continuity.

So I duplicated your setup with the M4 bolts and now it is working great.

Many thanks for your writeup A.J.

Great, glad to hear it. It's stories like this that make me feel like I'm not wasting my time by taking the time to document with pictures and a write-up. Plus my memory sucks so I can always go back to see what I did next time I have to do it.

[johnl]

Well done AJ. Thank You. Again.

[crusty shadow]

no special gasoline resistant wire is required for inside the tank? I am looking at doing this myself but the insulation falling apart in the fuel is a concern.
I may end up getting some jars and letting some samples of wire I have laying around soak for a couple weeks to see what happens.