Carbed 5.0

I hope you got the car for a steal, because otherwise you got robbed...

EFI to carb conversions are usually the result of ignorance upon the part of the person that did the swap. Not smart enough or too lazy to take the time to learn how EFI works, they bolt a carb & intake manifold on an EFI engine and never do the proper steps to fix the fuel pump and distributor problems they created. The quality of the workmanship is usually so low as to render the car unsafe to drive - the tip off is the EFI fuel pump and EFI distributor still in use on the now carb equipped engine.

Now that I have throughly insulted some of the carb guys, I will pass on some useful information...


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 - Rubber, Hydraulic and Industrial Hose - 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 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. 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. , McMaster-Carr or for the flaring tool you will need. Prices start at $85 and go up from there.

MSC Industrial Supply Co.


http://www.mcmaster.com/#flaring-tools/=b4fxc3


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 Crane Cams | Automotive Home Page for more information. Cost is about $400, which makes the 85 Mustang reman units look really appealing.

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 can be found if you are willing to dig through the self help repair section of their website.
See http://www.autozone.com/autozone/re...3835D6CFF5E3A5037BBBD332CF445FF.diyprod2-b2c3 for a starting point.

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.

No you won't,

I prefer mech gauges anyway.I believe they give a more accurate reading.

For the distributor, all you need is one out of an '85 GT...They can be had at Autozone for $70.00, just make sure it has a steel gear...

You dont need to change your brake booster

And for the fuel pump, you can keep the factory in tank pump and there are many ways to regulate the pressure...Heres what Im using

Professional Products 10653 - Professional Products Powerflow Fuel Pressure Regulators - Overview - SummitRacing.com

Personally, i wouldn't trust a fuel pump designed to push 40psi being regulated down to 6-7psi. If anything allows it to spike up fuel pressure, you're asking for a fire. I saw a guy at the strip once catch on fire because it started spraying gas out of the bowl vent tubes....luckily he wasn't running a hood and he saved the car.

I have an '89 coupe that I built 5 or 6 years ago.It was originally an EFI 4 cylinder.Converting it to a carburetor v-8 was fairly simple.I welded a sump in the tank and ran a holley pump/Fram filter set-up to the front.I still own this car and it was a fairly simple/cheap modification.If you don't feel comfotable welding the tank,by all means leave it to a professional!!!!Regulating the factory EFI to 6-8 PSI is NOT a solution.........

if the regulator returns the added psi to the tank same as the efi did why would that not work and be a $90 fix to a big PITA?

Convert it back to efi. I bet you get that it done faster, cheaper and the car will be more reliable and driveable.
Basic efi parts are fairly cheap and you can sell the carb stuff you have on ebay.

1bad67sbf said:

if the regulator returns the added psi to the tank same as the efi did why would that not work and be a $90 fix to a big PITA?

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Because you're putting your safety and your car in the hands of a $90 part, which if it decides to start letting 12 or so psi through instead of the 6 that you should be running, you could potentially burn the car to the ground.

For my money, for my car, for my safety, it's worth dealing with that PITA to prevent those risks....your mileage may vary. I tried the bypass regulator once on a guy's car and just did not like driving it...i went out of my way to convert his car over the right way with a mechanical pump because i couldn't live with the idea of his car burning down because i ran a bypass regulator.

I second converting back to efi. Stock parts are easy to find and relatively cheap.

ID89GT said:

I second converting back to efi. Stock parts are easy to find and relatively cheap.

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Who said it was stock? It may need better than stock parts to support his mods that he may have, and in that case it could be pricey

I'm in the same boat. Ive got an 89 5.0 fairly modified, and i would like to know what should be done to make it run 100%

I'm not sure i understand your brake booster question...they're the same thing. You get vacuum for the brakes from the intake.

purplestang90 said:

IVE GOT AN EFI CAR AND GOT WELL OVER 3000 IN THE FUEL INJECTION,JUST WANTIN A CARBED CAR BUT WANT TO DO IT THA RIGHT WAY,A COMPUTER WILL ONLY LET U DO SO MUCH!!!! AND IF I DONT HAVE TO CHANGE MY BRAKE BOOSTER THEN HOW DO I GET MY VACUM ??

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Out of curiosity how exactly does a mustang computer limit you? The stock computer on these cars is almost limitless, and needs no tuning.
$3000 in fuel injection parts? I'm guessing you are up over the 600rwhp mark?

If your vacuum question is worded correctly, you are in over your head.

what is the best way to take a efi fuel tank and change it to carb setup with mechanical fuel pump and still be able to go back to efi later?

Hey,, I have always said that using a EFI pump with a carburetor set up was a disaster looking
for a place to happen. But did you guys go to the summit web sight and read what this part is?
It's made pacifically for when a EFI car is changed over to carburetion. Might be something to it
If the regulator was made just for this it might be OK. Hummmm I'm on the fence on this one.