Discussion in 'Fox 5.0 Mustang Tech' started by purpl_stang, Aug 28, 2009.
What will I need to carb my car , including gettin rid of that wiring harness.
EFI to Carburetor Conversion
This article is for anyone with an '86-'95 Mustang that is contemplating converting from the Electronic Fuel Injection (EFI) to a carburetor.
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 drivability, 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 drivability 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. In the end I hope that whatever decision you make turns out to be the best for you and your car. GOOD LUCK!!!
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. The Building the Perfect Combo article on this website can help.
Fuel System: You will need a new fuel pump and pickup. Do NOT use the existing EFI pump. 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. The Mustang Performance Handbook Vol. 1 includes plans to build your own pickup if you decide not to shell out the $100 that it takes to buy an aftermarket one. 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 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 '88 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. Follow the Ford Duraspark II Ignition System article on this website to hook it up right. A complete MSD distributor and box could also be used as a step up from the factory stuff.
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.
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.
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. 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. This should include the following items:
--Air Bag connector below MAF
--Round 8-pin connector below MAF
--All 8 injectors
--Water temp sender
--Oil pressure sender
--Carbon canister solenoid
--ground at starter solenoid (single pin connector)
--Two connectors located near brake booster
I'm sure I'm forgetting something, but just disconnect everything you come to and the entire EEC harness will pull out. 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.
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.
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: MSD Ignition
The only thing is im wantin to lose the wiring harness completely for looks mostly, and i have a MSD Pro billet but it is for efi and i also have a 6AL box,the thingis that my car is a missed up on the vaccum and i dont think that Im gettin what the motors got, my car was a 4 cyl. and we took a 87 harness and converted to mass air and a A9L cpu it runns really good but the idling is not and i got small dead spot in my throttle.
thats nt a good reason to convert to carburated
Well Im really tired of fckn with it !
As far as the wiring, heres a writeup on wire hiding in a fox
Wire Cleanup For FOX Mustangs
I dont think he cares wether we approve of it or not
Go carb and you'll have to screw with it forever. Keep it EFI and figure out what the problem is (any codes?) and it will need no intervention, aside from normal, routine maintenance.
went efi to carb 2 years ago and havent had to do anything other than replace a leaky fuel fitting...oh, and the other problem I had was to decide wether I wanted to use all my former efi sensors/ecm as paperweights, or just visual reminders as to why I switched
StangGT1995 is right though, unless you have some carb knowledge, you might just be replacing the problems you have with a new set of problems that you might know nothing about...air/fuel mix, float level adjustment, choke, stuff like that
For ease of wiring I'd suggest going with an ignition box, and aftermarket gauges.
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. If you are too lazy to read a book and learn how EFI works, your carb car won’t run worth beans either.
Now that the rant is over, here’s some practical advice…
Do not use an EFI in tank fuel pump with a carb. A carb requires 6-8 PSI and the EFI pump puts out 40+ PSI. You will never get the pressure/flow regulated properly. If the add on regulator fails, the resulting overpressure will flood the carb and wash all the oil off the cylinder walls. Engine seizure and death will quickly follow. Either remain 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 - Rubber, Hydraulic and Industrial Hose - since 1919 for more information.
For stainless steel braided hose and fittings for automotive use:
See Search Results for stainless - SummitRacing.com
stainless steel hose - JEGS High Performance
See Eaton's Aeroquip Products for more information on High performance automotive hose products
The fancy red & blue 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 Industrial Supply Equipment from MSC Industrial Supply , McMaster-Carr or for the flaring tool you will need . Prices start at $81 and go up
Browse the MSC Big Book
While you are at the electrical part, you'll need a Durspark or similar ignition system with a mechanical spark advance. 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 Crane Cams for more information.
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.
Chilton's wiring diagrams
Gale Cengage Product Failure
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.
if you dont mind a little cross breeding, some guys use an hei module
how would that make things easier?
Interesting plan, but where does the spark advance come from?
The stock distributor used the computer to provide spark advance. You would still need an 85 5.0 Mustang distributor or equal to provide the spark advance and the steel gear for the roller cam.
Right, same distributor as if you were using the duraspark box, vacuum advance to carb metering block port (or some use full manifold vac depending on their combo)
After having a bad duraspark box, I went with the GM HEI after reading up and has proved very effective in my case
EDIT: Forgot to mention the HEI module comes with a packet of heat transfer paste but instead I spaced it with a couple of very small washers so the back is exposed to open air for cooling. They get hot on the back and you'll end up replacing it once a week if you mount it straight to the body
Bring it up to me in Bedford and I can tune the EFI to run alot better than any carb ever will
You must have never been behind the wheel of a properly tuned carbed engine
Realy???? is it going to run any better? No Is it going to use more gas? Yes
They arn't saying a carbed stang is going to run like crap. We are trying to talk him out of it b/c it is a LOT more work to do than just running the codes and tell the simptoms on here and there are a lot of people who know what they are talking about and are very good at tuning efi. Jr could probubly pin point the prob. with some codes and Oming (<< Is that a word?) some stuff out.
the EFI isnt causing or fixing vacuum leaks either.
Agreed. His problem more than likely would be solved using Jrichker's checklist.
However, he asked how to do it, not wether we agree/disagree with his decision
This thread is almost 2 weeks old. He's probably half done by now.
for whatever reason i cant stand carb conversions. i cant even stand it when people delete the a/c. hell im looking at ways to make an 84 project car efi now.