Need some HATZIE help! EFI Pump Power?

[SunSoaked]

In the middle of converting 85 to EFI. Installed new 87 tanks, sending units, EP381 pumps, 87+ selector switch, 6 port pollack motorized valve.

How do I power the pumps? Do they need a dedicated power source and how do they switch over when the tanks are switched. I read the diagrams for the TBI trucks but that uses the OEM ECM which I don't have.

Thanks in advance! @hatzie

Since posting this, I found out the pumps draw 5 amp @45psi so tapping into the hot wire on the sending unit should be fine.

Correct me if I'm wrong.

Thanks

[VetteVet]

Here is a wiring diagram for an 87. All modern vehicles use a fuel pump relay to power the pump. so it's getting 12 volts. The relay is controlled by the ECM and pump pressure.





I wouldn't use the sending unit wire for power, It may be a resistance to ground and could affect the gauge reading.

[SunSoaked]

Thanks VetteVet!

Thanks for the diagram. As you pointed out, I will run a dedicated power feed. Since I have Edelbrock Pro-flo EFI, I noticed in the instructions that it powers the pumps via the ground side. Whew...lucky catch. Nevertheless, it will need a relay.

[SunSoaked]

@VetteVet,

Thanks for the diagram. Here's my question/concern since I am keeping both tanks (Main & Aux). Since the power circuit runs THROUGH the factory selector switch it makes running new dedicated power feeds redundant and more complicated.

My options are to assume the selector switch (not the 6 way valve) is rated at the 6 amps the ep381 pumps draw and leave the wiring as is...or

Run an additional two relays after the switch and use the switches output to control a relay on each power lead to each pump.

Keep in mind I'll still need an initial relay to feed the power from the ignition because the Edelbrock EFI uses a NEGATIVE signal to turn the pumps on/off, so I got to reverse that to play well with the sending units which are grounded to the motor and chassis.

Geez, it's never just easy!

[VetteVet]

I can see a possible solution to power both pumps with the selector switch and not use the 6 amps plus, to run through the switch. I believe that the switch would handle more than that easily, as I see most of them are rated to 15 amps.

You may know this but You need 2 relays, one for each tank. You would run a full time live wire to no. 30 on each relay and connect the pump positive wires to 87 on each relay.

Then run a key on hot to the common terminal on a single pole double throw switch.

Then run a wire from each pole on the switch to the 86 terminal on each relay. This give you hot wire switching on each relay and pump.

Then run a grounding wire from the ECM to no 85 terminal on each relay so that the ECM can switch each relay and pump that you select. The ECM doesn't power the negative side of the relay or the pumps. It just switches the ground on the relays on and off to enable the relays to send power to the pumps, depending on which pump you want to run.

There are other ways to do this but I like it because it's simple to wire and should be reliable. You could fuse the power wire to no. 30 on each relay if you wanted to be safe.

I hope I understand how the system works and I have given you good information.

I reread your post and see that you already have a feed relay so you can just run it to the two pump relays. i don't think you will have a problem with the gauge sending wires or the pump grounds. You'll still be switching the pumps on and off on the negative side of the ECM.

[SunSoaked]

VetteVet,

I think you nailed it! That's a great solution. Keeps it simple and reliable. It also allows me to leave the OEM fuel system harness intact and just add the new "sub" harness to control the pumps. I'll just add a SPDT switch next to the factory rocker switch so they can be switched together when I want to switch over (Whew! Sorry about all those switches....lol).

It also retains the prime and safety shutoff feature built into the EFI because it just kills the negative output regardless of the position of the switch.

I drew it out on paper and it makes sense. Thanks for your help!

[VetteVet]

Originally Posted by SunSoaked

VetteVet,

I think you nailed it! That's a great solution. Keeps it simple and reliable. It also allows me to leave the OEM fuel system harness intact and just add the new "sub" harness to control the pumps. I'll just add a SPDT switch next to the factory rocker switch so they can be switched together when I want to switch over (Whew! Sorry about all those switches....lol).

It also retains the prime and safety shutoff feature built into the EFI because it just kills the negative output regardless of the position of the switch.

I drew it out on paper and it makes sense. Thanks for your help!

Well I studied it quite awhile and was gonna find a diagram I could modify to show you but I think you have it handled. Let me know if it works out for you.

[SunSoaked]

Originally Posted by VetteVet

Well I studied it quite awhile and was gonna find a diagram I could modify to show you but I think you have it handled. Let me know if it works out for you.

@VetteVet,

Just wanted to let you know I finally got this project finished. New tanks, sending units, pumps, and all associated wiring and switches.

It works perfect! Thanks again.