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20 Gal tank upgrade with Electric Fuel Pump

473 Views 0 Replies 1 Participant Last post by  Herbiesnerd
I have a 1990 YJ 4.2 with the BBD, mechanical fuel pump and a 15 Gal fuel tank. I just bought a new 20 Gal Poly tank and a Warrior skid plate. I installed a 1991 YJ in-tank Fuel Pump/Pickup assembly.
I plan on upgrading the BBD in the future with a Holly Sniper EFI (not even remotely interested in the Howell system) and that’s why I’m going electric with the fuel pump. I’m in California and currently the Holly Sniper is not CARB compliant so I’ll does this down the road. I’ll be adding a pressure regulator and I’ll just block off the old mechanical pump to fuel the existing carburetor which works well.

Here’s my question, does anyone know a shortcut on where I can trace to fuel pump wiring up front? I’m about to trace it all down but was hoping for help.

The original fuel sending unit has a 3 wire Weatherpack connector with only 2 wires from the sending unit. The 3rd wire port was a blank hole with a rubber plug. The factory wiring harness the sending unit plugs into has the 3rd wire, Orange/Black, already there so I’m going to take advantage of that. I cutoff the old connector and installed it to the new fuel pump (I have all the fancy weatherpack connector parts and crimper). I’m assuming that Jeep just used the same wiring harness for both the 4 and 6 cylinder that year. Since the 4 banger is fuel injected it has a factory electric fuel pump and that is what the Orange/Black wire is the for. I haven’t traced it under the dash yet but on schematics I’ve been pouring over, it looks like it ran to the MCU on the 4 cylinder.
The 4.2 MCU is not the same as the 4 cylinder so my MCU isn’t programmed to handle an electric fuel pump. I’m assuming that is where I should find the Orange/Black wire nearby.
I know I’ll need a relay and an oil pressure switch so this is my puzzle to figure out.

How to wire it and to where? Is there already a relay next to the battery I can use? Any help will be appreciated.