Jamesfarmtruck, welcome aboard!!!
The in tank primary pumps on the 1987 to 1989 trucks work fine.
As sixtseventwo4d mentioned: Start with bypassing the frame mounted high-pressure pump and disconnect the electrical to it.
You will still need a pressure regulator with a return because the in tank pump needs constant fuel circulation. Otherwise the pump will deadhead and fuel pressure will rise above rated pressure and fail. Constant fuel flowing through the pump keeps it cool.
Here is a picture of my regulator setup:
The supply line to the carburetor is kept as short as possible. It’s 16” long and the line is insulated with high temperature insulation.
The regulator is mounted on the bracket that secured EFI plenum to the head.
The Feed and return lines are also insulated with the same insulation. The feed and return are only insulated to the frame mounted fuel filter just under the cab near the bottom of the firewall.
In my case, a low pressure regulator was only needed since I’m only using the in tank primary pump that is rated to about 7 psi.
This setup has been reliable even in the hottest weather over 100+ degrees F. Even if the fuel boils out of the carb. The pump reprimes the fuel system to the carb immediately with no problems. In such hot weather, the only thing that I do to make the truck run normally when sitting for 10 minutes after shutting down is, once restarted, I blipp the throttle twice get fuel back in the carbs fuel circuit and then I’m off driving normally. This whole event that happens in just the hottest days lasts for about ten seconds. I might be able to eliminate this altogether if I use a heat shield and two carb insulating base gaskets.
Another picture to show the mounting location of the regulator. The bracket that secures the upper part of the EFI manifold to the head made installation simple.
The fuel pump relay on the driver side fender well stayed in place. The only thing I had to do was rewire it so the fuel pump would operate properly. I’ll cover this later today it’s very simple.
The inertia switch is still used. I wanted this safety feature to stay. Reason is if the truck ever gets in a bad accident. There is a better chance that the fuel pump shuts off if a driver becomes unconscious, or is unable to turn the ignition switch to off.
