Fuel Injection to Carb

A word of warning on EFI to carb swaps: don’t expect to pass emissions in any state that does comprehensive smog inspections, because it won’t happen. Be aware that you are violating several Federal laws concerning the removal of pollution control equipment. If you operate the vehicle on public highways and get caught by the Feds (doubtful, but possible) you could be subject to fines and imprisonment. You won't get any more power from a carb than you will from EFI.

The following information is intended for informational purposes only. Operation of a motor vehicle modified in such as manner as described below should be limited to off road use only.


Doing the swap: You must know how to read electrical diagrams and wire circuits properly to do the swap. Don’t take shortcuts or cut corners in the fabrication of the electrical or mechanical assemblies. If you do NASCAR quality work, the car will look good, run good and be as reliable as a carb’d car can be. Take pride in a job done with excellence.

If you do the hack job that is common among folks who don’t understand electricity or computers and are doing the conversion because it is easier than dealing with the EFI system, the result will look like and run like road kill. Wiring harnesses chopped up and spliced together with electrical tape, loose and dangling hoses, fuel lines spliced together with 3 types of fittings speak of ignorance and sloppy workmanship. If you can't do it right, don't do it at all. I wouldn’t wish a car with that kind of workmanship off on my worst enemy...

Now that the rant is over, here’s some practical advice…

Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. Either go full EFI or use a tank/fuel pump/fuel lines out of an 84 or earlier Stang. Fabricating your own setup is possible but there are some snags to overcome.

Do not attempt to leave the computer in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.

If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.

You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump. Do not try to wire the fuel pump without the relay. The 15-20 amps the pump pulls will overload the circuit. This will take power away from other items on the same circuit or cause the fuse or fuse link to blow.



You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.

For stainless steel braided hose and fittings for automotive use:

See http://store.summitracing.com/egnse...el+hose&searchinresults=false&N=+115&y=6&x=23

http://www.jegs.com/webapp/wcs/stor...hall&searchTerm=stainless+steel+hose&x=18&y=4

See http://www.aeroquip.com/pages/performance.html for more information on High performance automotive hose products

AN fittings require a 37 degree flaring tool. A standard automotive or household plumbing tool is 45 degrees and cannot be used with AN flare fittings.

See http://www.mscdirect.com/ , http://www.mcmaster.com/ or for the flaring tool you will need . Prices start at $75 and go up

http://www1.mscdirect.com/CGI/N2DRVSH?PACACHE=000000013509163


http://www.mcmaster.com/ctlg/DisplCtlgPage.aspx?ReqTyp=CATALOG&CtlgPgNbr=2252&term=Flaring


While you are at the electrical part, you'll need a Durspark or similar ignition system. The 85 Mustang GT 5 speed has a suitable Duraspark distributor with a steel gear compatible with the roller camshaft. Do not leave the computer in place in an attempt to control the spark advance. It will not work properly. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Durspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information.

I am in the same proscess of going form efi to carb. there are two main harnesses in the car the engine and the chassie the engine is pretty much all for the computer so I ahve a site that gives a basic over view of the removal of the efi harness the rest of the car can stay put. http://www.jason.fletcher.net/tech/efi-carb/efi-carb.htm