Results 1 to 11 of 11

Thread: wiring harness mod for fuel pump

  1. #1
    Supporting Member Turbo Mopar Contributor
    Join Date
    Jun 2006
    Location
    Spearfish SD
    Posts
    2,038

    wiring harness mod for fuel pump

    thanks to photobucket all my good saved links are dead now.

    anyhow, i'm changing over to a smec from the LM using a smec harness. basically rewiring everything. i vaguely recall there is something that "might" need to be done for the fuel pump wiring. is that correct? the cheat sheet i had said "see fuel pump notes" but the notes are missing!
    89 Voyager LE, 2.5T2 - rest in peace
    87 Charger Shelby T2 (2.4 conversion in process)

  2. #2
    boostaholic Turbo Mopar Contributor
    Join Date
    Mar 2013
    Location
    Columbia City, Indiana
    Posts
    1,222

    Re: wiring harness mod for fuel pump

    Not sure what you did, but I can tell you what I did on the Scamp. If you look at the wiring, the fuel pump, injectors, and coil power all come off the same wire from the ASD relay. The fuel pump comes off first, and draws the most current(especially when you use a Walbro 255 like I am). I personally think that is a very bad idea. So I used the fuel pump wire to actuate a 30 amp relay, and pull power directly from the battery to power the pump. I ran a much larger wire(12ga IIRC) all the way back to the tank for the pump. I fused the circuit right in front of the relay. By doing this, you take all the load off the ASD relay, and the coil & injectors get full current and voltage.

    Since I used a P-body harness, there was an extra lead from the battery positive for the heated rear window. I didn't need that for the Scamp, so that is the power tap I used to feed the fuel pump. If your donor SMEC harness came out of a car with a heated rear window(and you don't need it), you could do the same.

    Hope this helps.

  3. #3
    turbo addict
    Join Date
    Aug 2009
    Location
    Myrtle Beach, SC
    Posts
    2,133

    Re: wiring harness mod for fuel pump

    I don't remember having to do anything special with the fuel pump wiring when I converted my 85 l body to smec.

  4. #4
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
    Join Date
    Dec 2005
    Location
    Tuscola, IL
    Posts
    21,438

    Re: wiring harness mod for fuel pump

    I too don't believe there is a change wiring wise. I do like the idea of running it off the relay though. I also like the electrical bulk head connector which was posted in Carroll's TIII Omni thread. I'll probably use one to finish off the carb to turbo fuel pump conversion in my omni. I like that a lot better than what I currently have.

  5. #5
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,557

    Re: wiring harness mod for fuel pump

    A popular mod on GN's is to run a heavier gauge wire (12 or 10 IIRC) directly off the output post on the alternator through a relay.

    I don't think our cars have much issue with the pump wiring though.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

  6. #6
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
    Join Date
    Dec 2005
    Location
    Tuscola, IL
    Posts
    21,438

    Re: wiring harness mod for fuel pump

    Quote Originally Posted by Force Fed Mopar View Post
    A popular mod on GN's is to run a heavier gauge wire (12 or 10 IIRC) directly off the output post on the alternator through a relay.

    I don't think our cars have much issue with the pump wiring though.
    I've read some reports of a decent voltage drop from the battery to the pump.

  7. #7
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,557

    Re: wiring harness mod for fuel pump

    Yeah but when does it actually affect making power?
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

  8. #8
    turbo addict
    Join Date
    Aug 2009
    Location
    Myrtle Beach, SC
    Posts
    2,133

    Re: wiring harness mod for fuel pump

    I talked with shadow(Rob) about this when I was bothering him with build details on whether he thought it was necessary. He said he didn't see much gain from doing it. You are much better off running your current feed line as the return and using a bigger feed line if you are trying to make big power.

  9. #9
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
    Join Date
    Dec 2005
    Location
    Tuscola, IL
    Posts
    21,438

    Re: wiring harness mod for fuel pump

    Quote Originally Posted by Force Fed Mopar View Post
    Yeah but when does it actually affect making power?
    Not for the overwhelming majority of us, as we won't be affected by the pump's lower output with a 255lph pump. I am concerned more with the effect on the pump as a result of amps pulled and also the wiring for heat reasons.

  10. #10
    turbo addict
    Join Date
    Dec 2005
    Location
    Mesa, AZ
    Posts
    7,350

    Re: wiring harness mod for fuel pump

    Quote Originally Posted by wowzer View Post
    i vaguely recall there is something that "might" need to be done for the fuel pump wiring. is that correct? the cheat sheet i had said "see fuel pump notes" but the notes are missing!
    There is no "need" to change the fuel pump wiring. Although upgrading the fuel pump wiring might gain you 25% of fuel volume, and all it takes are some 10 gauge wiring, a relay, and mounting hardware, so why not?

    http://www.turbo-mopar.com/forums/sh...GLH&highlight=

  11. #11
    Supporting Member Turbo Mopar Contributor zin's Avatar
    Join Date
    May 2006
    Location
    ca
    Posts
    4,479

    Re: wiring harness mod for fuel pump

    ^^^This.

    If anyone has done this same trick with their headlights, they'll know just how much of a difference it can make in operational efficiency.

    When I've done flow testing on fuel pumps, voltage makes a huge difference in performance, both in volume and pressure potential. To be clear, the pump part is not changing, it's still going to move X amount of fuel per rev, but less voltage means the pump has less torque and therefore will slow under a given load, reducing volume, and with less torque, it can't "push" as hard to make pressure.

    The silver-lining here is that most folks have much more pump than they need, so a fairly small voltage drop won't have a noticeable effect.

    One other thing to keep in mind is that the factory wires were expected to carry only a certain amount of current, and with a much more power-hungry pump, they may start to become a liability, both from a heat and voltage drop standpoint.

    Bottom line, it's an easy mod that can add safety and reliability, and we can all use more of that with our 30(ish) y/old cars!

    Mike
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

    Bad laws are the worst sort of tyranny.
    - Edmund Burke

Similar Threads

  1. Flow numbers before and after fuel pump wiring in my GLH
    By tryingbe in forum Electrical & Fuel System
    Replies: 12
    Last Post: 03-11-2016, 06:50 PM
  2. Fuel pump/relay upgrade wiring
    By iTurbo in forum Electrical & Fuel System
    Replies: 31
    Last Post: 05-03-2014, 06:05 AM
  3. L body Fuel pump wiring
    By JohnnyIroc in forum "I need help!"
    Replies: 7
    Last Post: 04-24-2011, 03:54 PM
  4. Fuel Pump wiring pinout? '85 Omni GLH-T
    By JamesWilson in forum Electrical & Fuel System
    Replies: 2
    Last Post: 06-03-2009, 02:44 PM
  5. Fuel pump wiring questions
    By cj011 in forum "I need help!"
    Replies: 0
    Last Post: 05-10-2006, 03:51 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •