converting a 4.0 to carb

[sledneck07]

so i hate this efi crap with a passion but deal with it. i know you can get a carb intake for the 4.0s but what happens with ignition? does it still use the coil pack (i find that hard to belive if so) or seeing (from my understanding) that a 4.0 is a bored and stroked 2.9l will a 2.9l distributor work in place of the coil pack? just kinda wondering about this cauz i got a spare 4.0 and one that needs a rebuild.

 

[martin]

This question has come up many times over the last ten years or so.
the biggest issue as you assume is the distributor and even if the 2.9 dist. would fit it would not help you much as it has no mechanical or vacuum advance. The latest distributor with mechanical advance for the v6's is the one from a 79 pinto and the 2.8's have gear driven cams that rotate in the other direction. So even if it would fit you would have a gear issue. As far as I know, nobody has found an answer to the distributor problem.

 

[adsm08]

What is so bad about EFI?

It is more efficient and produces better power than a carb.

It produces better emissions.

It is easier to maintain.

It is less likely to break.


The ONLY advantage that a carb has over EFI is that a carb is easier to fix. Carb is still significantly harder to diag than EFI.


End of the line is that you are going to have a very hard time finding a dis to fit a 4.0. It would probably be easier to find, or even have made, and stand alone controller for the ignition system.

 

[Nhaz]

I have to disagree on the diagnosis of a carb being harder then a EFI to diagnose.

I have owned both and if you have a funky computer problem which I have had on several vehicles over the years you can be pulling hair out since everything checks ok but it doesn't work right.


Carb. rather simple. if its got fuel and spark it will generally run. If it doesn't theres usually something really wrong with it that probably doesn't have anything to do with the carb.

EFI not so much. 1 injector down is a pain in the butt to fix. heck a bad signal wire could take hours to track down.

I will agree that EFI IS over all more reliable and much more efficient then the carbs. carbs are just way easier and faster to fix.

 

[gwaii]

if i were doing this i would first get a 2.9 distributer to confirm that it fits the 4.0.it should,but i've been caught out on this sort of stuff before.if it fits,that's a template.get a duraspark distributer from an early 80's 300six,and see what the difference is compared to the 2.9 unit.you should be able to machine the 300 dist body to fit and the shaft to fit the 2.9 gear or the 2.9 gear to fit the 300 shaft.as long as the gear turns the topside of the distributer you will be ok.then the only problem might be the large dist cap from the duraspark needing more firewall clearance.a ballpeen hammer will take care of that.edit-oil pump drive will be different-you my need to adapt the 2.9 shaft to the 300 body....compare parts;anything can be done if you really want to.

 

[Jason]

EFI is easy for those with the tools and understanding. The ECU practically tells you whats wrong.

 

[twentyover]

Use the2.8 distributor, knock the roll pin out of the drive gear and replace it with the drive gear from a 2.9 dizzy or the 4.0 oil pump drive/cam position sensor

 

[03ranger4x4]

im wondering if you can leave the computer in, just for spark purposes. And have the carb on it? if you have too just build a resistor bank, adding up to the resistance of the orginal injectors and plug that into the computer harness, so it will run correctly. I dont see why this wouldnt work, any ideas?

But honestly, i would keep the efi, and just get it fixed. Ive never had any major issues, reguarding efi, and i find that the computer basically tells you whats wrong, if not gives you a good starting piont is a great aid to troubleshooting.

 

[Big Jim M]

Nope!

im wondering if you can leave the computer in, just for spark purposes. And have the carb on it? if you have too just build a resistor bank, adding up to the resistance of the orginal injectors and plug that into the computer harness, so it will run correctly. I dont see why this wouldnt work, any ideas?

But honestly, i would keep the efi, and just get it fixed. Ive never had any major issues, reguarding efi, and i find that the computer basically tells you whats wrong, if not gives you a good starting piont is a great aid to troubleshooting.

The computer controls the timing as well as the fuel mixture. The carb would be so much richer than the computer desires it would futch the timing and the engine wouldn't run worth a crap.
You'd have to have a dist with full advance available...either full mechanical or partly with some vac advance also.
Big JIm

 

[03ranger4x4]

The computer controls the timing as well as the fuel mixture. The carb would be so much richer than the computer desires it would futch the timing and the engine wouldn't run worth a crap.
You'd have to have a dist with full advance available...either full mechanical or partly with some vac advance also.
Big JIm

doesnt the computer know the fuel/air ratio via the o2 sensor? So in theory couldnt you just put a resistor in the o2 sensor circuit so the computer thinks its running at a good mixture and therefore the timing would be normal, basically what you would want to do is make the computer blind to how the engine is really running and trick it into thinking its running how it should be so the timing is normal? idk, maybe it cant work that way. i havent messed with efi that much to know if it would work. I do know my old bronco II ran fairly well with every single sensor disconnected, including the map sensor ( i ran it for a brief moment just for shits and giggles)

 

[sledneck07]

its just an idea ive been batting around latley for when i get to building a buggy. i dont want to deal with the efi sensors and the masses of wire, just going for simple and easy and one of a kind, heck i have 2 spare 4.0s and drivetrains so im set just gotta get steel and at the rate im at that could be a few years unless my paycheck gets a hole lot fatter.

 

[AllanD]

Use the2.8 distributor, knock the roll pin out of the drive gear and replace it with the drive gear from a 2.9 dizzy or the 4.0 oil pump drive/cam position sensor

It isn't simply a matter of the dizzy gear the 2.8 distributor is designed to rotate in the opposite direction thus the advance would actually work BACKWARDS...

Do remember that the 4.0 with it's EFI makes more power and torque than a production carb'ed 302 did.

And don't bring up the performance versions of the 302 because they were even peakier than the EFI-HO engines were.

I've lost track of how many times I've mentioned (without anyone "Getting it")
that the 5.0HO makes it's peak torque at 3400rpm and until it gets to 3000 or so a 4.0 will romp all over it.

Ford did an amazingly good job in designing and calibrating the 4.0 and most people completely miss the point.

the 4.0 as built makes it's power where it's actually used.

AD

 

[Beleneagle]

What about if I wanted to upgrade from my very tired 2.9 to a 4.0. From what I've read so far everything will swap over with the small issue of the starter. The 4.0 uses a bigger flywheel/clutch as well as I understand as well. I was hoping that a 2.9 distributor/cam would work in the 4.0 so I wouldn't have to make any wiring changes other than the starter. I was thinking if one used the 2.9 cam (if it fits, and the spec's aren't too different) than you might be able to used the distributor. Since the truck came with the distributor set up then the wiring would still work as well. What's the Major difference between the two engines with respect to the cams. I was thinking that the oil drive that sits in place of the distributor might just be a easy swap, but I guess not........



David

 

[twentyover]

It isn't simply a matter of the dizzy gear the 2.8 distributor is designed to rotate in the opposite direction thus the advance would actually work BACKWARDS...

The helical angle on the distributor and 4.0 oil pump drive are mirrored, the distributor for the 2.8 turns clockwise, as does the oil pump drive for the 4.0 oil pump. Another check would be comparing firing orders between the 2.8 and 2.9, which, while having cams rotate oppostite directions, are both clockwise distributors

 

[feellnfroggy]

DOnt convert a 4.0 to carb. Period. Its just my opinion, but one worth listening too. If you want carb that bad, find yourself a factory carbed 302. Otherwise stick with the EFI. Its just common sense.