EFI To Carb Conversion

why have you decided to carb it.i converted mine from aod to 5spd and efi to carb but only because the car would NOT run correct no matter what with the efi set up.your going to need a new distributor,intake,carb,gaskets,fuel pump,fuel line,throttle cable,ignition system(msd) and you have to do some wireing.you will no longer have a working factory tach no either.

FWIW, you might want to consider doing the T-5 swap first, because with an EFI-to-carb conversion, you're going to need some specific linkage adapters on the carb and a Lokar TV cable for the AOD, which would be a waste of money if you plan on ditching the AOD for a T-5 later, anyway.

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 state or federal law enforcement (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 are one of those few people who do excellent work, please disregard my negative comments. They are not intended for you.

Quality, quality, quality…
Some of the motivation of my negative comments about carb to EFI has to do with the quality of electrical workmanship. A lot of the wiring “repairs” that I have seen on the road and in the junkyard looks like road kill. The other part of my negative view stems from people who can’t grasp the operation and tuning of EFI. Carbs have their own set of requirements and some learning is required to get the best performance. Every car is different and each installation needs to be tuned to get the best performance. Putting an “out of the box carb” or one from someone else’s car isn’t the way to success. There is no auto compensation for small variations in carbs like there is for EFI. Just throwing a carb on a car because you won’t bother to learn how EFI works is a poor excuse.


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 EFI 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 Amazon Hose and Rubber - Industrial Hoses and Hydraulic Hose Assemblies since 1919 for more information.

For stainless steel braided hose and fittings for automotive use:

See summitracing.com

stainless steel hose - JEGS High Performance

See Eaton Aeroquip > Performance Products 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. If you do, the flare is subjected to too much stress when the fitting is tightened, and is likely to fail or leak.

See MSC Industrial Supply Co. Home Page , McMaster-Carr or for the flaring tool you will need . Prices start at $77 and go up

Browse the MSC Big Book


Tube Flaring & Expanding Tools


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. 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 CraneCams for more information.

Tools needed:
Crimp tool for connector pins $9-$30 AutoZone, NAPA, Advance Auto Parts or other store
100-150 watt soldering gun (recommend WELLER 8200PK soldering gun kit 100/140W) $30 at Lowes or $40 at Home Depot
3/32”-1/8” rosin core electrical solder, 1/4 lb roll $6 at Ace Hardware, Home Depot or Lowes
Assorted sizes of heat shrink tubing. Buy long pieces and cut length to fit. It is cheaper that way. Parts-Express.com - Heat Shrink Index: 2:1 Ratio, 3:1 Ratio, Heat Shrink Kits
Hot air gun to shrink the tubing ($30-$40) Home Depot
Jeweler’s screwdriver kit $5 at Ace Hardware
Assorted automotive wire, 18-16 gauge 10’-20’ foot spools in different colors. $5 a roll at Advance Auto Parts.
Ford connector pins AutoZone, NAPA or other store $5-$10 for a kit of 10-12 assorted pins

You will have $110-$150 in materials and tools if you don't already have them.

The water temp and oil pressure signals feed from the sender to the main harness through the 10 pin EFI engine harness. To utilize these senders, you need to identify the wires and find a way to reconnect them to the main harness after the EFI engine harness is removed. You need a weatherproof quick connector to join the sender wiring to the main harness.


You will need to construct a wiring harness from the ‘85 carb distributor to the Duraspark box if you go Duraspark, or other distributor to coil wiring.
The voltmeter picks up its signal from the switched voltage present on the instrument panel, so you don’t need to worry about that.

The fuel tank gauge is also independent of the computer wiring.

AutoZone wiring diagrams

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model Mustangs

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model Mustangs

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-98 model Mustangs


How to solder like a pro - Ford Fuel Injection How To Solder Like a Pro a must read for any automotive wiring job.

Soldering pigtails onto existing pins is road kill quality work as far as I am concerned. Take some time to study the way the Ford connectors are assembled and you will find that a small jeweler’s screwdriver will release the pins from the connector shell. New pins and a crimping tool are available from the Standard Motor Parts or Bendix Electrical parts line that the NAPA & Bumper to Bumper Auto Parts stores carry. Ask any auto parts store about Standard Motor Products or Bendix Electrical wiring parts. Those that carry them will be able to get the parts you need. AutoZone has a cheap kit with 10 pins for about $5. Just enough pins to leave you short when assembling a connector.

One of the interesting things about the Ford OEM wiring diagrams is that the connector shape on the drawing matches the connector shape in the car. That makes it easier to identify connectors and circuits. OEM Ford diagrams are available at for an 85 Mustang at Helm Incorporated: Search Results or can be found in the Chilton series of auto repair manuals for Mustangs.

The following is an excellent idea from a fellow Stangnetter who tackled the wiring plan the right way. He obtained the wiring diagrams from an 85 carb'd V8 Mustang and laid them out side by side with the diagrams from his car. He then traced out each circuit and the wire colors and connectors associated with them. After tracing the circuit and connectors for a circuit, he laid out the changes he needed to make. One circuit at a time made a difficult big job into many smaller easy to manage jobs.

Double post - ISP hiccuped.

I guess you could always sell off the AOD linkage and cable parts with the tranny afterwards.

I just had to come to the T-5-before-the-carb-swap conclusion, myself, because I realized I'm going to have to fart around with that stupid TV linkage issue if I go with any kind of carb while I still have the AOD ... since only the CFI cars came with an AOD in '84 or '85, apparently no factory-carb'ed Mustangs ever had an AOD. Plus, my AOD uses a rod instead of a cable, anyhow, so it'd be kind of an additional PITA aside from the usual issue of trying to get an AOD properly adjusted. Soooooo, I'm just going to skip the extra step and expense by doing my T-5 conversion first before I tackle the CFI-to-carb swap ... plus I'll be able to more accurately feel how much of a difference in power afterward will be due to the CFI-to-carb swap rather than how much power was being soaked up by the AOD.

Btw, you might want to consider going with a GM HEI ignition module for your ignition. Cheap, readily available, and (supposedly) gives a better spark that the TFI setup. Wiring it up is pretty simple and it uses a Duraspark distributor (also cheap).

Darkwriter77 said:

Btw, you might want to consider going with a GM HEI ignition module for your ignition. Cheap, readily available, and (supposedly) gives a better spark that the TFI setup. Wiring it up is pretty simple and it uses a Duraspark distributor (also cheap).

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I posted about that in one of these recent conversion thread. If you go over to Carbed Ford Message Board :: Home, they have a ton of cool stuff like that. You get the module from a parts store...it's like a '70s Camaro part and it's only around $20 and supposedly puts out 50k volts and is comparable to your typical MSD box (minus the rev limitor, which is the big down side to this setup).

85_SS_302_Coupe said:

I posted about that in one of these recent conversion thread. If you go over to Carbed Ford Message Board :: Home, they have a ton of cool stuff like that. You get the module from a parts store...it's like a '70s Camaro part and it's only around $20 and supposedly puts out 50k volts and is comparable to your typical MSD box (minus the rev limitor, which is the big down side to this setup).

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True. But if you're running an auto, it's not as much of an issue. And you could always add a stand-alone aftermarket rev-limiter, as well. (Think I saw one in Summit's last catalog for like $120.)

MSD makes a really nice limiter, they call it a "soft touch" limiter because it doesn't cut off so violently. They're about $90. I don't have a limiter right now and it's down right scary when the tires break loose because the RPMs spike so fast that i know i've hit 7k a few times.

msd ignition in mine with a 6k chip,very simple to wire up,its a good unit and you run your aftermarket tach off it easily as well because you wont have a factory one anymore.i had my car carbed with an aod for a short time but i had to manual shift it,PITA.i would do the 5spd first if i was you.as for a fuel pump,just buy the holly blue pump,external and mount right in the back and as far as fuel lines i used almost all the factory lines and still utilized the factory fuel filter.just got like 15ft of 3/8 fuel line to do the little bit in the back from the new pump and into the tank and then the little bit up front from the factory chrome fuel line to the regulator and from there to the carb.i used the factory chrome line that comes up the the rails and just cut off by the connect and put the new hose on there.its not that hard and i guess it just depends how extensive you really want to get with it.

When doing this do I use the factory ignition coil?

tmartintk said:

When doing this do I use the factory ignition coil?

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You are better off starting a brand new thread in this instance. List all of the pertinent information about your current setup and ask away whatever specific questions you have. This is much more likely to yield a better response from the other members

@jrichker A suggested post edit. Resent research on alcohol based fuels and the water they can hold is showing them to be very corrosive to aluminum. If there was even a chance of E15 to E85 being run in the car, I would not want aluminum fuel line. I will also be sure all the rubber hose I use from now on to be alcohol compatible.

7991LXnSHO said:

@jrichker A suggested post edit. Resent research on alcohol based fuels and the water they can hold is showing them to be very corrosive to aluminum. If there was even a chance of E15 to E85 being run in the car, I would not want aluminum fuel line. I will also be sure all the rubber hose I use from now on to be alcohol compatible.

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You are correct. Most aluminum tubing is 6061 alloy, and I haven't checked its corrosion resistance in a water/gasoline environment. Something else to spend my idle time doing...

7991LXnSHO said:

@jrichker A suggested post edit. Resent research on alcohol based fuels and the water they can hold is showing them to be very corrosive to aluminum. If there was even a chance of E15 to E85 being run in the car, I would not want aluminum fuel line. I will also be sure all the rubber hose I use from now on to be alcohol compatible.

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I checked on the corrosion resistance of both 1100 pure aluminum and 6061 aluminum alloy and they are some of the most corrosion resistant aluminum products. One of their uses is for food and beverage cans. The acid and water found in most soft drinks, canned citrus and tomato products would tend to be more corrosive that the water/alcohol/gasoline mix in motor fuel.
So if you stick with 1100 or 6061 aluminum tubing, corrosion from the water/alcohol/gasoline mix shouldn't be a problem.

Thanks for checking. I read the articles them see the Stabil 360 ads about proud castings and wonder if we should run diesel! When I was starting out (fossil fuels still had fresh bones), I ran a piece if 3/8 copper for fuel line to eliminate hose on a carb car. The next mechanic that saw it promptly replaced with zinc coated steel line. Do you know if that was necessary?

7991LXnSHO said:

Thanks for checking. I read the articles them see the Stabil 360 ads about proud castings and wonder if we should run diesel! When I was starting out (fossil fuels still had fresh bones), I ran a piece if 3/8 copper for fuel line to eliminate hose on a carb car. The next mechanic that saw it promptly replaced with zinc coated steel line. Do you know if that was necessary?

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I have never seen a copper tube in any factory stock car. All I can say is that steel tubing on automobiles is the current OEM standard. It may be because steel is less expensive than copper.