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Title: EFI to Carburetor Conversion Summarized Procedure
Post by: Joel5.0 on June 12, 2008, 05:56:29 pm
EFI to Carburetor Conversion

I. Introduction
This article is for anyone with an '86-'95 Mustang that is contemplating converting from the Electronic Fuel Injection (EFI) to a carburetor.

II. Why Are You Converting?
The first question you should ask yourself is why. Why do you want to go from fuel injection to carb? If your car is a daily driver that is fairly stock then you are just wasting your time and money. Your gas mileage will decrease, you will lose some low end torque, you will lose some drive-ability, you will increase your exhaust emissions, and decrease the value of your car. If you have a street/strip car and are looking for a cheaper way to build more power then a carb setup might be for you. If it is a race car and you don't care about drive-ability then a carb is a smart choice. Don't get me wrong, a good well thought out carbureted combo is a very good system. But if you are switching to a carb just to solve your problems with EFI you might be surprised. A carburetor requires work to get it right. You may be trading in your problems for a whole new set of problems that you know nothing about. Before doing anything carefully weigh out your decision to remove the factory system from your car.

III. Mechanical Changes
Intake and Carburetor: Of course if you are converting from EFI to carb you must have an intake manifold and a carburetor. Just be sure to size the components to match your combination properly.  A 600 CFM Vacuum Secondary Carburetor, properly tuned, will work with a myriad of combinations - a good rule of thumb is to error on the side of caution and use a smaller carburetor than what you think would work best.

Fuel System: You may need a new fuel pump and pickup. While many people will tell you ?Do NOT use the existing EFI pump?, I have found that you can use the factory pump up to 400 FHP.  If you are building a stroked Windsor - you should look to the aftermarket for the proper fuel system.  I recommend Aeromotive?s Mustang specific kit.  If you do plan on using the stock 88lph fuel pump (you can not use anything above a stock pump for this type of setup - the return line is not large enough to work properly and you will burn out the pump or seriously flood the car and create a fire hazard), you MUST use a return style regulator.  You can also use the stock fuel lines up to the same 400 FHP figure.  If you wish to use a new fuel pump and pickup, you can either use an electric low pressure pump designed for a carb (like the Holley red or blue pumps) or go with a mechanical fuel pump. In either case you must replace the fuel pickup on top of the gas tank with a purpose built pickup that does not include an in-tank pump.  These in-tank pickups are made by Mallory, Vortech, Paxton and a few others.  If you are above the 400 FHP or if you have a drag car it may be time to upgrade to a fuel cell or modify your existing tank for a bottom sump. At this time I would also recommend you go with new fuel line from the tank to the carb. Use 3/8" minimum or larger based on your needs. Remember that many sanctioned race tracks will only allow up to 12" of rubber fuel line so go with aluminum wherever possible, and keep the lines in-between the frame rails for safety. To use a mechanical fuel pump you must change the front timing cover on the engine to one that accepts a bolt-on fuel pump. You may also need a fuel pump eccentric to drive the pump. My '89 motor had one from the factory but I have heard of some roller motors that do not have them.

Ignition: Replace the distributor with one from an '85 manual transmission Mustang. This distributor has a steel gear to be compatible with a roller cam. Also use a Ford Duraspark II ignition box (use the blue one for a Mustang).  A complete MSD distributor and box could also be used as a step up from the factory stuff.  You can also use an aftermarket buzz box (MSD 6al, Mallory Hy-Fire, Crane, etc.) and use the appropriate adaptor harness for a Ford Duraspark distributor. 
Brackets & Linkage: Any fox body accelerator linkage will work as long as the car was equipped with a carbureted V8. Look for a '79-'85 V8 Mustang or an '83-'88 V8 T-bird if you go junkyard searching. You will also need the throttle cable bracket attached to the intake manifold and a throttle return spring.  Lokar makes a nice aftermarket piece, but it can be pricey.  You can reuse you existing EFI cable - but it is really long and looks like a hack job when attached to the carb.

Transmission: This is probably the most critical step of the whole process. If you have a manual transmission you have nothing to worry about. However, if you have an AOD automatic you need a TV (throttle valve) cable. You can purchase this from Lokar Performance (NOTE: this is the same cable that Windsor-Fox Performance carries except $25 cheaper from Lokar direct). Setup is critical so follow the instructions included closely. Setting up the cable wrong will lead to a burned up transmission in very short order.

IV. Electrical Changes
The electrical changes described here are for a 1990 Mustang. All '89-'93 mass air equipped ?Stangs will be very similar. '86-'88 speed density and '94-'95 mass air ?Stangs will also be close but some changes will be necessary. The best method to keep the wiring straight is to purchase a Chilton's Manual that includes wiring diagrams. Compare your car's wiring to the 1990 Mustang wiring. By using this outline and the correct wiring diagram the job will be much easier.

Your car is divided into two harnesses; the EEC harness and the main or "chassis" harness. The EEC harness contains all of the computer related sensors, actuators, and such. It also contains some of the wiring for the air bag system. The chassis harness contains everything else; headlights, fuel pump wiring, instrument cluster, etc., 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:

--Two connectors near the computer (passenger-side kick panel). One is green, one is gray. Both are 8-pin connectors I believe. One is rectangular and the other is round.

--Two connectors near the driver's side hood hinge and right above the master cylinder. One is gray, one is black. They are both round, 8-pin connectors. One of the connectors does not utilize all 8 pins.
The first thing to do is the part that's the most fun! LOL Disconnect the battery (of course!). Remove the computer and the EEC Power relay that sits directly 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 ( do not force it, just be patient and it will wiggle out). 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. You will be shocked at how much all that copper weighs..LOL
Once you've got everything out, it's time to start re-wiring. All the re-wiring will take place at the two connectors by the brake booster that you unhooked earlier. This is how you will tap into the chassis harness and get things like the fuel pump working again. Best way to accomplish this is to tap into the wires just below the connectors. I use those little plastic splice connectors...works great. Be sure to tape up the open ends of the connectors to prevent water from getting in there.  (It should be noted that the 86 EFI harness? is not completely stand alone, three wires will have to be cut at the firewall.  These three wires are for the fuel pump relay.  The red wire will get a constant 12v source, the yellow wire should be spiced into the red/light green wire on the gray harness, and the tan/green wire must be grounded.)

If you've got a Chiltons with the wiring diagrams in it, I will include the reference numbers for each wire if you'd like to look them up.
On the Gray Harness:
---Wire #16 (red/light green - 16 Ga) to the ignition trigger/turn-on lead. On my MSD it's the thinner red wire.
---Wire #11 (Dark Green/Yellow - 20 Ga) to the negative side of coil or the "tach out" port on an MSD. This is the line to your stock tach.
On the Black Harness:
----GROUND #97 (tan/light green - 18ga) to a suitable chassis ground. This creates the ground for the primary side of the fuel pump relay.
---Wire #39 (red/white 20ga) to the temp sender.
---Wire #31 (white/red 20ga) to the oil pressure sender.
---Wire #361 (red 16ga) to #16 (the wire you ran to the ignition turn-on above). This creates the positive voltage supply for the primary side of the fuel pump relay.

My car already had A/C delete, so I didn't mess with the WOT cut-off. Only other thing that you need to do is when wiring in the fuel pump itself. Just get the polarity right on the two wires that are coming off the stock EFI pump. I cut them and extended them out to where my Holley Blue is.
On the underside of the car, you can disconnect the O2 sensors and oil level sensor (side of oil pan) and pull that harness out too. I didn't mess with it, but you could rewire the oil level sensor to still be operational if you wanted.

After that, you should be good to go! As far as wiring the ignition, you'll have to run wires to the positive side of the battery and chassis ground as well as wire the pickup to the distributor. If you've got an MSD, the diagram can be found at msdignition.com.

Just in case you didn't know, the smaller the gauge (Ga) of a wire, the bigger around it is. That should help you to distinguish between the right wires. Your fuel level gauge will still work properly (providing you didn't put an old carb tank in the car) and your ammeter should work fine as well.



Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 02:34:32 pm
Joel, maybe you can clear a few things up for me as I've started the wiring on the carb conversion. I already have the efi wiring harness out. My car is an 89'. I don't have a chilton I have a Haynes and in the Haynes 89' and 90' V8 is the same.

Well on the gray harness connector above the booster I pulled the pins out for the 2 wires I needed.

(http://i533.photobucket.com/albums/ee335/orange395w/Grayharness.jpg)

Red/Light green and Dark Green/Yellow. I ran the Dark Green/Yellow wire to the negative side of the coil, but I'm unsure of where to land the Red/Light Green. What would be considered the "ignition trigger/turn on lead"? I'm using a mallory hyfire box. http://www.summitracing.com/parts/MAA-685/?rtype=1

I decided to skip that and move my attention to the black connector above the booster.

(http://i533.photobucket.com/albums/ee335/orange395w/Blackharness.jpg)

The first wire that I came to says Tan/Light Green. There is not a Tan/Light green wire on the black harness. However there is a Tan/Light Green wire at the green connector on the passenger side kick panel. Is this the harness that it was referring to?

(http://i533.photobucket.com/albums/ee335/orange395w/Kickpanelharness.jpg)

Next if I am not using the factory temp sender or oil pressure gauge I can exclude wires #39 and 31 correct?

 I would like to get this wired up before the Carb and the rest of the parts get here.

Thanks for the help.  :smile


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Joel5.0 on July 05, 2010, 03:28:02 pm
The following might help...

(http://fordfuelinjection.com/images/harness03.gif)





Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 03:50:50 pm
Can't say that it does. I'm still lost as far as the original instructions go. There is no tan/light green wire in the black harness for the fuel pump relay ground.

Wire #16...is this the main power wire to the ignition box?





Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: liljoe07 on July 05, 2010, 04:49:48 pm
That wire changes color when it goes through the black connector. Thank ford for that.

On the black connector. Dash side. There should be a Yellow wire with a red stripe right next to a pink wire with black stripe. Yellow wire with red stripe is what you are looking for. That's what the tan/ light green wire goes to on the engine harness side for the fuel pump relay ground.

All you really need to do is ground it on the body close to the fuel pump relay.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 05:07:44 pm
That wire changes color when it goes through the black connector. Thank ford for that.

On the black connector. Dash side. There should be a Yellow wire with a red stripe right next to a pink wire with black stripe. Yellow wire with red stripe is what you are looking for. That's what the tan/ light green wire goes to on the engine harness side for the fuel pump relay ground.

All you really need to do is ground it on the body close to the fuel pump relay.

I have a red wire with yellow stripe, but no yellow wire with red stripe.

Even on the other side of that connector. The side that went to the EEC there is not a tan/light green wire???


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: liljoe07 on July 05, 2010, 05:16:01 pm
Look at the code test port. There should be one terminal with 2 wires in it. That's the fuel pump ground circuit. Whatever color that is, is what you would be looking for on the engine side black connector. See what wire corresponds to that on the dash side.

You are messing with black 8 pin connector by the brake booster correct?


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Joel5.0 on July 05, 2010, 05:17:08 pm
Did you check the diagrams at http://sbftech.com/index.php/topic,3993.0.html ? Red/Lt green would be the IGN ON wire for the coil or ignition box


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 05:30:15 pm
Look at the code test port. There should be one terminal with 2 wires in it. That's the fuel pump ground circuit. Whatever color that is, is what you would be looking for on the engine side black connector. See what wire corresponds to that on the dash side.

You are messing with black 8 pin connector by the brake booster correct?

O.k. I must be an idiot, but looking at the test port there is a tan/green wire, but it does not have 2 wires in it. The port with 2 wires in it is grenn and black/white.

Yes I am messing with the black connector by the booster. Will this wire be directly on the relay under the seat?

This is very frustrating because I don't know shit about electrical.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 05:33:33 pm
Did you check the diagrams at http://sbftech.com/index.php/topic,3993.0.html ? Red/Lt green would be the IGN ON wire for the coil or ignition box

So if I connect the red/light green wire to the ignition red wire that goes directly to the battery I'll be good?Sorry I'm such a rock with this stuff, but I seriously need this stuff spelled out for me. I appreciate you guys taking the time.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: juiced coupe on July 05, 2010, 05:36:26 pm
Did you check the diagrams at http://sbftech.com/index.php/topic,3993.0.html ? Red/Lt green would be the IGN ON wire for the coil or ignition box

So if I connect the red/light green wire to the ignition red wire that goes directly to the battery I'll be good?Sorry I'm such a rock with this stuff, but I seriously need this stuff spelled out for me. I appreciate you guys taking the time.

No. The main power wire still goes to the battery. The red/green wire goes to the switched/ignition wire.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: liljoe07 on July 05, 2010, 05:41:44 pm
Yes that wire will be on the fuel pump relay under the seat. Not sure what you have going on. But I gave you wire colors from my connectors on my car. Which is an 89 coupe also.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 05:42:36 pm
Did you check the diagrams at http://sbftech.com/index.php/topic,3993.0.html ? Red/Lt green would be the IGN ON wire for the coil or ignition box

So if I connect the red/light green wire to the ignition red wire that goes directly to the battery I'll be good?Sorry I'm such a rock with this stuff, but I seriously need this stuff spelled out for me. I appreciate you guys taking the time.

No. The main power wire still goes to the battery. The red/green wire goes to the switched/ignition wire.

O.k. Thanks. Brain farted on that one. Let me go find where I landed that one. Likely in my fuse panel.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: liljoe07 on July 05, 2010, 05:43:04 pm
Go ahead and tell me what wire colors are on the fuel pump relay. I can tell you which one to ground.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 05:45:01 pm
Yes that wire will be on the fuel pump relay under the seat. Not sure what you have going on. But I gave you wire colors from my connectors on my car. Which is an 89 coupe also.

Joe can you double check to see if you had the colors backwards? I have a Red/yellow stripe wire on the black connector next to the pink/black wire, but not a YELLOW/RED wire.



Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: liljoe07 on July 05, 2010, 05:54:18 pm
I am looking at right now. Its a yellow wire with red stripe. On the same 4 wire row as the pink/black wire. Right next to it.

More than likely the same wire. Just some used a different coded wire but same colors. Turn the key on and make sure it doesn have 12v. If it doesn't, temporarily add a jumper from it to a ground. Cycle the key and se if the fuel pump relay clicks.


Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: Orange395w on July 05, 2010, 06:00:39 pm
I am looking at right now. Its a yellow wire with red stripe. On the same 4 wire row as the pink/black wire. Right next to it.

More than likely the same wire. Just some used a different coded wire but same colors. Turn the key on and make sure it doesn have 12v. If it doesn't, temporarily add a jumper from it to a ground. Cycle the key and se if the fuel pump relay clicks.

Thanks. I will have to wait on that as I don't have the fuel system hooked up yet. The feedline is capped off. I have no regulator or carb or anything yet.



Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: azhatchback on September 21, 2010, 06:39:56 pm
I am looking into converting my car and found a few problems with jason fletcher's  procedure. I have an 88 and used a haynes 79-92 mustang & 79 - 86 capri manual. I maped out all the wiring. I cant tell you if this is for all years but this applies to my 88. First off you need to go by the wire color that runs into the fire wall not the side that goes to PC and sensors.
Here are the items that are incorrect.

Wire #97 - Ground, Tan & Light Green. This does exist but it is in the green conector in the passanger kick panel by PC. As another guy stated it is also in the test port but that does you no good as the test port will be tossed with the main harness. This ground wire goes to pc pin 22  designated as "feed back carb coil". This is what you ground out. It is wire #97 and is in kick panel not in the black connector. I traced it all the way from the fuel pump schematic.

Wire # 361 is not wire 361. It is wire 787 and is pink / black. Tie this into wire #16 red and light green on grey conector and there you go. Fuel pump is powered. The rest of the artical is correct.  Atleast for an 88 it is.

Louis Wood



Title: Re: EFI to Carburetor Conversion Summarized Procedure
Post by: kennygunit on August 27, 2011, 11:22:10 am
I just pulled a 351w EFI motor and going to convert it to a carb.

As weird as this sounds, i find working with a carb a lot more easier than having to deal with EFI for road racing.

Thanks for the article, it was very good!