Mustang fuel injection to carburetor conversion
Since I told a couple of the mailing lists that I am on that I converted a Mustang from fuel injection to carburation, I have had several people ask for the details. I have posted a summary for you here.
1) The fuel pump. Fuel injection uses a high pressure puel pump. Many people will tell you that you can run the in tank pump with a regulator before the carburetor. However, I have found that this is not advisable, especially if you do not run a return line, because the pressure will creep with the pump running and the car not running. I have personally seen this, and if you have 40 PSI at the input to your carb, you will destroy the needle valves. So, what I did is run an electric pump outside of the gas tank. Since Holley advised me not to run 40 PSI into their pumps, I replaced the in tank fuel pump with a carb pickup line. I swapped tanks with an earlier Mustang (83-85 Mustangs use the same size tanks, and fit right into place). However, the older sending units use a different resistance value, and will screw up your fuel level readings. I later noticed that if I had removed the sender from the 83-85 pickup and just put that pickup in the 87-93 tank, that I would have been able to use the 87-93 sending unit and the 83-85 pickup tube. The moral of the story is, get the 83-85 pickup, remove the sender from it, and place it in place of the fuel pump in your current tank.
2) The fuel pump can be wired to the existing harness for the fuel pump , but when the EEC computer is removed (see further down) you have to solder the trigger wire for the fuel pump relay to ground and the +voltage feed to the FPR to an Key On Ignition wire.
3) Since you will be installing an engine without any of the nifty sensors
normally found on an FI car, the computer will have no inputs, rendering
it pretty much useless for controlling spark. The cheap way to get around
this is to install a Duraspark III distributor, and appropriate
support pieces, like the ignition module and coil. The parts are cheap and
plentiful, considering the number of vintage cars with this engine
(302 or 351), and the Duraspark III ignitions are strong enough to
fire consistantly to about 6000 RPM. Plus, when you want to step up
to a higher quality ignition box (ala Hi6 or 6AL, etc), the Duraspark
distributor is a piece of cake to hook up.
4) Since the computer is no longer controlling fuel or ignition, you may as well remove it to get rid of some extra weight. (It's really amazing how much all that copper wire weighs). Remove kick panel in front of EEC. Disconnect 8-pin harness going to: Fuel pump Trigger, Ign+, AC wot wire, Signal ground, power feed, and a couple others I don't remember. Remove the EEC and the EEC power relay (right above EEC). Remove the harness from the inside of the car, from under the hood. Wear gloves unless you like tearing your fingers open when the rubber plug in the firewall pops, like I did. Then for the Chassis harness (the one that comes into the engine bay from the drivers side), you have to save the following wires: Oil pressure sender, Temp Sender, Tach feed, IGN, 1 Power wire (the one in the same harness as all the rest of the chassis wires). That's about it. If you want to use the fuel pump relay and the inertia switch to drive an electric fuel pump in the back of the car, you have to short a few wires in the harness disconnected by the EEC. IGN to FPR+, Ground to FPR-.
That's it. Your car should now be ready to run with a carb.
NOTE: If someone is converting to a carburetion setup and is removing the stock 5.0 pieces and would like to make a little money off them, the people on the Early Bronco Mailing list and the Northwest Vintage Bronco Mailing list and to the Colorado Bronco Registry mailing list are always interested. These folks really appreciate the cast off pieces like computers, stock throttle bodies, fuel pumps, mass air meters, intakes, etc. Most of them will never see above 5K rpm so the stock stuff is *more* than adequate and really helps out with 'wheeling since it's not upset by offcamber work and compensates for altitude changes. The contact person for all three mailing lists is Coby S. Hughey, who can be reached at email@example.com.
Help out a fellow Ford nut and pass along those pieces that would otherwise sit in the garage collecting dust!
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