EFI to Carburetor Conversion

My first EFI to carb. conversion allowed me to see first hand the difficulties behind this conversion. You should first ask yourself why you are doing the conversion. If its to fix a problem that you are having with the fuel injection, you might want to consider if switching would actually be worth it. Although the EFI to carb. swap isn't brain surgery, it does require extreme modifications to the car, and if it's your daily driver I would strongly recommend against it!

However, if the car is your streep/strip fun car, and you are just wanting a cheaper way to get more HP/torque, then the conversion might be right up your alley! The carburetor requires a little extra work to get it tuned properly, but is well worth the extra horsepower that lies within! Before any decisions are made, weigh all factors and see what the best route for your specific application may be.

Intake and Carburetor

1. The first obvious change is the intake manifold and the carburetor. The choice for my application was the Victor Jr. intake and a Holley 750 double pumper. These two choices were made after many opinions and lots of legwork were done. They now are sitting on top of the 351w that I chose to replace the 302 with.

Fuel System

2. The fuel system is the next major modification that I addressed. I opted to go with an electric fuel pump from Holley (Blue). Again I was trying to keep the application as simple as possible. And using the existing EFI fuel pump is not an option, although it can be modified to work, it is easier AND cheaper to use an aftermarket electric pump. Now is a good time to consider using the existing fuel tank or switching to a sump tank, or in my application, a fuel cell. I opted for the fuel cell for budgeting reasons. Again, spend your money where you can make extra horsepower! I went with a Summit stainless 10 gallon fuel cell because its much lighter than that huge stock tank that we cut out! You will have to make some modifications to the trunk floor to use the fuel cell however, if you want it to look pretty, but 10 minutes with a cutter and its all good!

I used 3/8" stainless fuel line from the cell to the pump and then on to the regulator mounted under the hood. The stock fuel lines will just not cut it. I have heard of people using them and running very well, but I figured I was spending all this money might as well protect the investment. You don't want to skimp on cheap stuff here either, they tell me a broken fuel line is no fun! Also keep in mind here some of the rules of the governing bodies of racing. Some only allow up to 12" of rubber hose within the fuel system, so be sure to know your regulations if they are applicable to your buildup.

Electrical System

3. The electrical changes will be the fun part! To be safe I would advise first of all to disconnect the battery. This may seem a bit odd to advise, but trust me I have read about horror stories on the corral about people not disconnecting the battery. (Remember the air bag post!!) My second piece of advise would be to by a Chiltons manual or go one step further and purchase the wiring diagram for you ford Mustang. I have the number and address if you need it! Your car is divided into two harnesses, the EEC harness and the chassis harness. The EEC contains all of the computer related sensors, actuators, and such. The chassis harness contains everything else, ie headlights, fuel pump, etc. In order for the EEC to receive power from the battery, control fuel pump, and the airbag to work properly, the two harnesses must mesh together at some point. There are 4 of these points throughout the car: Two near the computer near the passenger side kick panel. Both are 8 pin connectors, one green, one gray. One is rectangular and one is round. The other two are near the driver's side hood hinge and right above the master cylinder. One is gray, one is black. They ar eboth round, 8-pin connectors. One of the connectors does not utilize all 8 pins however.

Remove the computer and the EEC power relay that sits right above the computer. On the 60-pin connector that plugs into the computer, remove the black plastic "cap" which holds the wire bundle at a 90 degree angle to the connector. Unplug the two 8-pin connectors mentioned above, unscrew the bare wire ground and you should be able to pull the harness up into the engine compartment. The oval-shaped grommet will come with the harness, so use a screwdriver to pop it out of the hole. Once you've got that done, everything you need to remove is under the hood. Just start at one end of the harness and work your way around and disconnect everything you come to that attaches to the EEC harness. As a minimum, you're going to have to remove the upper intake to get to all this.

I ended up completely replacing the entire engine so the engine bay was completely bare when I was doing this, which made it a lot easier! I also replaced the stock ignition with a complete MSD ignition. I ran a Painless wiring box out of the cab that controlled the electric fan, the fuel pump, starter, and also wired it to run the headlights and taillights on command (Had to keep the streetability just in case! LOL) If you take this route, be sure to keep all the instructions! The MSD system: 6AL box, distributor, and coil, all wired up pretty easily with the painless harness, and I would highly recommned this to you first timers.

If you have any further questions just drop me an email, I will be happy to help all that I can. I am currently working on the 460 project so I will have the information posted on that one hopefully early next year!

Thanks especially to Fletch's Carbureted 5.0 Mustangs which I used as a bible to do this project