1988 300 efi to carb questions

Jamesfarmtruck

New member
Hi, i have a 1988 ford f150 4.9L M50d.
im doing a efi to carb conversion on my truck and so far i have everything figured out, except the fuel.
I heard that the efi system uses around 40-50psi which is too much for the carb.
is there any way to bring it down to its recommended carb psi (which is i think supposedly 7psi?) without using a regulator?
Ive heard you can do something with the pumps in the fuel tank to bring it down but i need more information? Help. Thank you.
 
Your 88 should have a supply pump in the tank. The high-pressure pump is on the frame rail, driver's side. Simply bypass the high-pressure pump and disconnect the electrical to it also (no need in letting it run). You should then check the pressure to make sure the in-tank supply pump is adequate to use; as some get weak over the years and may not do well. Most carb pressure requirements are in the 3-4 psi range.
 
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:
IMG_1667.jpeg

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.IMG_1668.jpeg

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.
 
Last edited:
Here is the pressure regulator and fuel pressure gauge that is being used.

 
If you dont want to swap distributors you can put a tps mounting bracket onto the carb and swap your sensor from the throttle body to that bracket on the carb. Might have to extend the wiring. Good luck, id like to hear your results as i have heard others say they regret doing the conversion.
 
Hi, i have a 1988 ford f150 4.9L M50d.
im doing a efi to carb conversion on my truck and so far i have everything figured out, except the fuel.
I heard that the efi system uses around 40-50psi which is too much for the carb.
is there any way to bring it down to its recommended carb psi (which is i think supposedly 7psi?) without using a regulator?
Ive heard you can do something with the pumps in the fuel tank to bring it down but i need more information? Help. Thank you.
I converted a '90 to carb. It lost power and economy took a big hit. The main reason is the ignition system swap. The EFI head requires precise timing control, and there is NO aftermarket or Ford centrifugal/vacuum advance distributor that will be right for it all the time.
If you can keep your EFI ignition system, it will greatly enhance the swap to carb. What InlineDave87 suggested above- speaking from experience!-
I highly recommend. It will be some work. You need to keep the intake manifold sensor, throttle position sensor, MAP sensor, Coolant temp sensor and the Knock sensor. . I know mine would be much better, especially economy, if I had kept the factory ignition system with the carb.
 
Back
Top