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Electric Fuel Pump Install

R

rsh4364

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MarcusOReallyus said:
I don't recommend this approach. Run power from a solid power source (battery or the 12v buss on the firewall) to a relay, and switch the relay from an appropriate source on the fuze block.

That wiring is old, and some of it is already overloaded. Why add to the load?




acesneights1, that's really good info about the OPS. To add an override switch for priming purposes would be very simple.

Does the OPS interupt power or ground to kill the pump?
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Im electricly stupid and my pump is wired to fuse box also,could you post some numbers for the relay best for this application.I did install relays for headlights and offroad lights but they came in kit.So I have no idea what I need relay wise.
 
MarcusOReallyus

MarcusOReallyus

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No problem! :beer:

Since you have the thing already wired into the ignition at the fuse box, we'll use this to switch the relay. So, don't start your project by ripping this out! :D

But DO start your project by disconnecting your batteries!

Now, automotive relays have a numbering standard that makes life easier. Any 20 or 30 amp automotive relay will do fine for this job. Just shop around to make sure you get one that is numbered, like this guy. Oh, that's the first thing we need - a parts list.

Okay, here we go:

  1. Relay.
  2. Inline fuse holder, with a 10 or 15 amp fuse.
  3. 14 gauge wire. (Preferably red, since it will be a power lead.)
  4. 18 gauge wire. (Not red, and not black. Anything else is fine.)
  5. 18 gauge wire. (Black. This will be a ground connection.)
  6. Assorted electrical connectors.


Alright, we gots parts. Now, some assembly required!


  1. Find a good location for your relay. Preferably out of direct exposure to water. You can mount it now, or wait until you get everything hooked up.
  2. Run a 14 gauge wire from a solid power source (battery or the 12v block on the firewall) to the place where your relay will be, and from the relay location to the fuel pump.
  3. Run an 18 gauge wire from a switched hot location on your fuse block (your existing power feed will be just fine) to your relay location.
  4. Run a black 18 guage wire from a good, solid ground point to your relay location.
  5. Connect the black ground wire.
  6. Connect terminal 87 on the relay to your fuel pump using some of your 14ga. red wire.
  7. Connect terminal 30 on the relay to your good 12v power source lead (using some of your 14ga. red wire). Final hook up of power will be the last thing you do. (You can just take the fuse out and make all your connections.)
  8. Connect terminal 85 on the relay to your 18 ga. black ground wire.
  9. Connect terminal 86 on the relay to your 18 ga. switched power lead.
  10. (You can actually swap 85 and 85. It doesn't matter as long as switched 12v goes on one and a good ground goes on the other.)
  11. Verify your connections both for electrical integrity and to ensure you got it right:
    • Relay Terminal 87 goes to fuel pump hot lead. 14 gauge red wire.
    • Relay Terminal 30 goes to good 12v power source (but it's not completely hooked up yet). 14 gauge red wire.
    • Relay Terminal 85 goes to ground. 18 gauge black wire.
    • Relay Terminal 86 goes to switched 12v.
  12. If it all checks out, make the final 12v connection (put fuse in fuse holder).


Fire it up! :beer:
 
MarcusOReallyus

MarcusOReallyus

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As for what kind of relay, it's a pretty standard item. Bosch used to be a good brand, but they got out of the business. If you find a source for NOS Bosch, jump on it. Hella is also excellent, like this guy:

http://www.amazon.com/HELLA-9654000...ie=UTF8&qid=1410005827&sr=1-24&keywords=relay

If you want to make life easy for future maintenance, you can get a pre-wired socket for the relay to plug into:

http://www.amazon.com/Parts-Express...ie=UTF8&qid=1410005827&sr=1-17&keywords=relay


Basically, if the bottom of it has the same pins and numbering as this guy, it's good to go.

http://www.the12volt.com/ohm/basics.asp
 
R

rsh4364

Active member
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greensprings ,ohio
MarcusOReallyus said:
As for what kind of relay, it's a pretty standard item. Bosch used to be a good brand, but they got out of the business. If you find a source for NOS Bosch, jump on it. Hella is also excellent, like this guy:

http://www.amazon.com/HELLA-9654000...ie=UTF8&qid=1410005827&sr=1-24&keywords=relay

If you want to make life easy for future maintenance, you can get a pre-wired socket for the relay to plug into:

http://www.amazon.com/Parts-Express...ie=UTF8&qid=1410005827&sr=1-17&keywords=relay


Basically, if the bottom of it has the same pins and numbering as this guy, it's good to go.

http://www.the12volt.com/ohm/basics.asp
Click to expand...
Relays ordered,Thanks.
 
C

chevywood

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Hey guys, wanted to see how this turned out as I was looking at doing the same thing. I think I have an air leak and fuel drain problem. Anyway, the relay that MarcusOReallyus linked is a 24v relay. Being electrically stupid will it also except a lower voltage as power was coming from the 12v block or does it reduce voltage if coming from 24v source.
 
trooper632

trooper632

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Cant you just bypass the mechanical fuel pump all together by running the fuel directly to the fuel filter from an electric pump and leave the old mechanical pump on the motor?
 
llong66

llong66

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trooper632 said:
Cant you just bypass the mechanical fuel pump all together by running the fuel directly to the fuel filter from an electric pump and leave the old mechanical pump on the motor?
Click to expand...
Trooper632, yes, you can do what you asked about. I did this temporarily until I get my turbo installed. There is a small brass "T" on the frame, right under the firewall. The steel line from the tank stops and restarts there. I just ran a new line straight up the firewall to the filter input. You might still want to remove the push rod from the mechanical pump. The fuel flowing through the mechanical pump lubricates the rubber diaphragm inside, without that lubrication, I have heard that the diaphragm can crack and you end up with a huge oil leak from the mechanical pump. I suppose if you remove the pump to get to the push rod, its up to you at that point if you wana just put the pump back on or buy a block off plate.
 
trooper632

trooper632

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Ok, the mechanical pump is leaking terribly, that's why I was just going to see if I could leave it on there. I have tried to install one of these before and it was such a pain, I never could get it in there right, so I guess I will get the plate for one
 
Recovry4x4

Recovry4x4

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Big Tex said:
All -
I have looked all over trying to find a part number for the fuel pump on my M923A2. Does anyone know a part number?
Click to expand...
I doubt you will find that here, this is the CUCV forum.

You will find it in the parts TM for your 939 series truck though. From there use google and parttarget with the factory number to get you moving in the correct direction.
 
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