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EFI to Carb

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BigBear300
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Location: Christiansburg, VA

EFI to Carb

Post #1 by BigBear300 » Sun Dec 20, 2015 3:44 am

I am pretty mechanical, but I have never done this before so I need some help.

I was wanting to swap my EFI to a Carb. I know opinions very, but I am old school and I just want simple (Computer/sensor free), because I religiously believe that computers and trucks should not be mixed.

I was thinking about doing an Offenhauser intake manifold with a Holley 390. I was also considering boaring out ether .50 or .60 over. I am going to keep the EFI exhaust manifolds, and I know that I need a Duraspark 2 distributor and a fuel pressure regulator, because of the high PSI that my dual tank pumps produce. That is about the extent of what I know, so any contributions to this post would be greatly appreciated. Thanks in advance for taking your time to read and answer.
1994 Ford F150 XL, 4.9L EFI, 2WD, M5OD-R2, 8.8" 3.31 Diff, Tow Package, P235/75R15

Daderka
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Re: EFI to Carb

Post #2 by Daderka » Sun Dec 20, 2015 7:01 pm

Mine is a feedback carb, Im switching it all over and putting the EFI exhaust on it. In my 6 months search of not wanting to fork out 280 for a intake I found 2 this week. 1 came with lots of other stuff and I drove 4 hours to get yesterday. The other is one craigslist in lower lousiana for $180 but he was going to ship it to me for that (im in Indiana). Jump quick if your going to do it! As for everything else...dont know mine was already set up DS2 also.

Good Luck!
85 F250 with one lost driver.

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bubba22349
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Re: EFI to Carb

Post #3 by bubba22349 » Sun Dec 20, 2015 9:10 pm

:wow: you will be in for a huge project to convert an EFI truck over to a carb system. Besides what you have mentioned don't forget you will also be doing almost a compleate rewiring or modding of all the electrical systems and you might also have to change out the dash gauges to be compatible with the older pre EFI engine gauge senders. Best of luck with it. :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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BigBear300
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Re: EFI to Carb

Post #4 by BigBear300 » Mon Dec 21, 2015 4:45 am

bubba22349 wrote::wow: you will be in for a huge project to convert an EFI truck over to a carb system. Besides what you have mentioned don't forget you will also be doing almost a compleate rewiring or modding of all the electrical systems and you might also have to change out the dash gauges to be compatible with the older pre EFI engine gauge senders. Best of luck with it. :nod:


Yep, you're right, I forgot about that part. I'm probably just going to get a donor truck 1980 to 84 and swap a lot of stuff over, and use aftermarket gauges. Yeah, between that and the M5OD to C6 swap, I am going to be busy-busy. What a man will do for his wife and his truck.
1994 Ford F150 XL, 4.9L EFI, 2WD, M5OD-R2, 8.8" 3.31 Diff, Tow Package, P235/75R15

Fordman75
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Re: EFI to Carb

Post #5 by Fordman75 » Mon Dec 21, 2015 8:51 pm

Why are you considering a .050" or .060" over bore?
Ted

54 Ford F100/F150 4x4
300, NP435 4spd, NP205 transfercase

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BigBear300
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Re: EFI to Carb

Post #6 by BigBear300 » Tue Dec 22, 2015 4:52 am

Fordman75 wrote:Why are you considering a .050" or .060" over bore?


To drop in 360 or 390 pistons.
1994 Ford F150 XL, 4.9L EFI, 2WD, M5OD-R2, 8.8" 3.31 Diff, Tow Package, P235/75R15

Sick6Turbo
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Re: EFI to Carb

Post #7 by Sick6Turbo » Wed Dec 30, 2015 12:41 pm

Malory 4309 regulators have worked fantastic for me over the years. They can be used with turbo's and n.a. Can be had used on ebay.

Duraspark2 requires only 1 hot wire to run the whole system. It has 2 hot wires that go into the cab, one is energized on the crank circuit (I believe to up the voltage to the coil) and the other wire is energized in the run circuit. I have run either or and no issues. I will check my truck and let you know which wire is which to be safe. The system is grounded through the distributor. DO NOT ground either of the wires in the 2-wire conector coming out of the module.

Instrument sensors should not be an issue, Not sure if the tach will work with tach output on the duraspark.
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

Sick6Turbo
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Re: EFI to Carb

Post #8 by Sick6Turbo » Wed Dec 30, 2015 12:57 pm

Malory 4309 regulator have worked fantastic for me over the years. They can be used with turbo's and n.a. Can be had used on ebay.

Duraspark2 wiring link: http://handymandanonline.com/ford_duraspark_2.html

Instrument sensors should not be an issue, Not sure if the tach will work with tach output on the duraspark.
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

Sick6Turbo
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Location: Almond, Wi.

Re: EFI to Carb

Post #9 by Sick6Turbo » Wed Dec 30, 2015 2:08 pm

Almost forgot...the computer will need the tach input to keep the electric fuel pump running. Google search should show the wire that is needed from the tfi module connector. Not sure if the computer will accept the duraspark tach signal.

However, the ignition switch provides positive power to the fuel pump relay and the computer controls the negative to the relay, cycling and turning it off and on. Cutting the negative wire and grounding it(relay side, just tape up computer side of wire) will keep the fuel pump running anytime the key is on.

Double check to make sure inertia switch will still shut off the fuel pump. Unbolt it and whack it on your hand to open the circuit.
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

Sick6Turbo
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Re: EFI to Carb

Post #10 by Sick6Turbo » Thu Dec 31, 2015 11:43 am

I did a Cummins swap in a 99 Super Duty that had a v10 manual trans.

Adapted all the v10 sensors to the engine. (easy except tach)

99 v10 tach requires 2 pulses per revolution. It's mounted by the camshaft sprocket (turning half engine speed of course) with 4 triggers on the sprocket. Took the Cummins harmonic balancer to the machine shop and had another notch machined into in so there would be 2 total, 180* from each other. Made a bracket to mount the v10 sensor, and whalla! tach works.

One wire, hot with key to control fuel solenoid.

Removed electric fuel pump from tank and replaced with siphon tube. The Cummins engine had a mechanical fuel pump on the motor to feed the injector pump.

Moral of the story: Everything worked. Power windows, gauges, speedometer, starter, alternator....the engine computers are usually very much independent from the rest of the truck. They control the injectors, ignition, fuel pump, and usually electronic auto transmissions. Looks like you have those covered. :thumbup:
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

Eff1 Shifty
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Re: EFI to Carb

Post #11 by Eff1 Shifty » Sun Jan 17, 2016 3:01 pm

If you had an extra carb'd engine and an efi truck, how hard would this actually be to do? I just bought an old carb'd engine and was originally going to use just the block and keep efi. Now im contemplating just switching to carb. I want more power and with efi thats hard to do for a reasonable price. couldnt i use an old gas tank and fuel pump to retain a working gas gauge and fuel system? If i just removed the engine harness all the lights and ignition (im hoping) would still work?? It seems like a simple idea in theory...I guess i'd have to go to an older style 4 or 5 speed too. If someone could point out all the things to consider that would be great.

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woodbutcher
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Re: EFI to Carb

Post #12 by woodbutcher » Tue Jan 19, 2016 11:40 am

:hmmm: One little hint when going to the DS2 setup.Run an extra ground wire from one of the mounting screws for the DS2 box to the fire wall or some other suitable spot.Have run DS2`s like this for appx 200k miles with no problems.EXCEPT,for when "Mother Nature"killed the brain box and the extra one in my tool box.Lightening hit a power pole about 10 feet from my truck.Most troublesome.Had to walk about a block to the parts house to get another one.
Good luck.Have fun.Be safe.
Leo
"People never lie so much as after a hunt,during a war,or before an election".
Otto von Bismarck

arse_sidewards
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Re: EFI to Carb

Post #13 by arse_sidewards » Sat Jan 23, 2016 12:15 am

The computer needs input from the sensor on the distributor, not the tach although the tach signal may suffice (is it a square wave?)

The EEC-IV system is pretty much independent. The megaquirt site has some good info on ignition systems.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

Eff1 Shifty
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Re: EFI to Carb

Post #14 by Eff1 Shifty » Sat Jan 30, 2016 2:53 am

Ok so while im quite passionate about mechanics in general and I always am looking for more knowledge, Im without formal education. So there are bits that I feel im missing when it comes to things of this nature. All that aside what are the things to consider in an efi to carb swap in an f150 at least? As i understand it i'll need a block mounted fuel pump which comes on the carbd motor obviously. To retain a working gas gauge I would need a sending unit out of a carb'd truck? That could mount directly in my efi tank or..? I would need to at least disconnect the ecu. If i wasnt concerned with cosmetics in theory couldnt I simply unplug the ecu more or less and just use the body wiring harness for things like lights, turn signals etc? would I run into issues with the ignition in some way? As far as gauges go id like to retain the speedometer, oil pressure, temp, volts (i guess pretty well all of them lol). would a carb'd motor and m5od work together without any mods?? I get the feeling that this forum is more for the people already "in the know" to an extent, but if you would humor me! Auto forums shouldnt be for elitist guru's exclusively I feel. We're all here for the same reason (i hope) and that is to further our knowledge in things we're interested in. granted ive tied a few on, so im sure Ive left some obvious thing needed for a swap like this to actually happen, but bare with me. Any information would be appreciated, thanks!!

Sick6Turbo
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Re: EFI to Carb

Post #15 by Sick6Turbo » Sat Jul 09, 2016 10:16 am

The cheapest way to convert...

Drop the fuel tank, remove fuel pump, add a piece of fuel hose in it's place to draw fuel 1/4" from the bottom of the tank.
Remove the in tank rubber check valve from the return line, as the return line will now be the vent.
The tank is now the same as a carb vehicle and the gas gauge will still work properly.
The inline fuel filter will act as the "sock filter" that is normally in all gas tanks.

Up front, connect the bigger 5/16 fuel line to the mechanical fuel pump on the block. Adapters are available to convert the spring connection to a hose barb. I think they are actually intended for mending. Be sure there is a filter between the pump and carb as well.
Connect the 1/4 return line (now vent) to an inline fuel filter to help keep dirt and moisture out of the line and tank. Droop it down with a length of hose into the fender well area or somewhere without much air movement.

Connect the DS2 with 1 hot wire that has power with the key on and still hot when cranking.
Use the efi temp and oil pressure sensors on the carb engine and connect.

Done.

Everything in the truck will work. If you switch transmissions, as long as you plug in the cable, the speedo will work.

1 step at a time, don't over think this. A carb engine needs 1 hot wire and filtered fuel with a vented tank to be happy. The rest of the truck does not need the ecu unless the trans is electronically controlled, where you would have to stay efi for load sensing or run an independent control unit for the trans.
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

arse_sidewards
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Re: EFI to Carb

Post #16 by arse_sidewards » Mon Jul 11, 2016 7:41 am

Eff1 Shifty wrote:I get the feeling that this forum is more for the people already "in the know" to an extent, but if you would humor me! Auto forums shouldnt be for elitist guru's exclusively I feel. We're all here for the same reason (i hope) and that is to further our knowledge in things we're interested in.


It's a low power economy engine that hasn't been produced in twenty years. Of course only the people who are really dedicated to the platform are still talking about it. The people who aren't serious don't stick around here and it gives the impression that everyone here has been here forever. Look at any other forum for comparable niche interest. The majority of the people who are into it at all are all-in.

If you don't mind learning (and doing lots and lots of reading and researching) you'll be "in the know" soon enough :beer:
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

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