I expect that getting rid of the computer, et. al. would have a negative effect on gas mileage, especially if everything was working properly before. The computer could control timing and fuel mixture based on engine load and other parameters much more accurately. In the very early days of emission controls you could make improvements in performance by removing things, but with the advent of the computers it's not likely. I think that most of the devices and schemes that improve emissions (other than the catalytic converter, air pump and possibly the PCV valve) also also cause fuel to be burned more efficiently in the engine.

 

After I junked the TFI crap,and went to a NON feedback carb,my gas milage went UP by 4 MPG.
And that is before I have done any fine tuning.
Leo

 

Exactly! I was hoping for at least 2, would have settled for 3, and would have been tickled with 4.

 

I currently get 12 MPG with a non-feed back carb that had to change out last year due to the stock feeb-back carb pissing extra gas down the carb throat. Still using TFI ingition but have a new DS2 vac adv dissy to install soon as it get warm out.
With my current setup I get NO advance. It runs at base timing only ~10 deg or so.
I am hoping to get 16 MPG after swaping out the dissy and having VAC ADV again.

I am also a alittle worried about pulling out the computer and what it might effect... like does my tach run off the computer?

I have an 1986 F150 I6 4x4 C-6 auto, 3:50 gears with 235-75-15 tires. Also have AC which will cycle on and off to keep the system pressurized year around, sometimes I unplug the connector on the compressor in the winter. Still have the air pump but might take the belt off to see if it help the MPG.

It seems to me that the guys that get the good MPG have the OD trans and the gears and the patience to go slower... to cruise at 2000 RPM instead of 3000 RPM. I am at ~3000 RPM at 65-70 mph with my setup.

 

That's about where I am at with the 4spd granny low tranny. Except I am only getting 11mpg.

We seem to have several here doing pretty close to the same thing, only we have different trannys. I sincerely hope we keep this thread going, as I am sure I can get more out of mine.

Franklin 2 posted that the dizzy vacuum line needs to be hooked up to a source that has no vacuum at idle. I've got good vacuum to mine all the time. Does anyone think that if I find a source that has none at idle I will notice a difference, in power or mpg?

 

Yeah of your old computer system is shot, you will see an increase of milage. If it was in top working order, you can see a decrease.

You need to find a carb that is calibrated to not give you vacuum at the vacuum advance port at idle. Some calibrations of carb and distributor, require vacuum at the vacuum advance port all the time. 99% OF Those calibrations are feedback carbs. My truck is one of these for instance.

When you do this type of swap, you really need to get the Carb and the distributor at the same time, and choose a calibration, that matches them both, for best performance.

Choose a carb off a 1980 as example, and get the 1980 distributor to match the carb, etc.

 

Yes sir, I learned that after the fact, but I do have another carb to try. I thought I'd check all of the vacuum ports to see if I can find one that is more suitable for right now, and I may try that Carter/Motorcraft when it warms up a little.

Can you run that first part past me one more time? I thought that we were eliminating all of the computer crap when we did the swap, I assumed that this would be a non issue. I was trying to go for a setup like for instance from the mid seventies, tuned well, and getting somewhere around 15.

 

With the carb, and distributor swap, to DSii, there is no need for the computer anymore. Just the Ignition module.

Once the carb, and distributor are matched, 1980 to 1980, 1978 to 1978 etc,,, all that computer stuff is just added weight.

 

This is the statement that confused me.

 

It look to me that it is the same P/N distributor 75-87 for the F150... that is if you trust the parts guy

Cardone Ignition Distributor

Part Number: 302669


For Your Vehicle


Vehicle: 1983 FORD F-150 PICKUP
Engine: L6 4.9 Liter 1BBL

Ignition Distributor: Remanufactured; Without Module; With Vacuum With Single Vacuum

See all vehicles this product fits

 

I would have to disagree. This whole thread is proof. A 75, 6, 7, up to whatever year will have the vac. advance. 87 down to whichever year won't, my 85 did not. UNLESS that vacuum advance part is not a part of the dist., that just doesn't make sense.

 

The Vacuum advance is a part of the distributor.

Although you can fit one type of distributor from 1965-1987 and beyond it does not mean it will be calibrated right for your engine.

There is dual vacuum advance and single. there are distributors that require ported vacuum, and some that require both ported and manifold vacuum. and the centrifical advance may have heavier or lighter springs, etc...



Match the year of the carb with the year of the distributor, and you shouldn't have problems. even if other distributors will fit and may look the same.

I remember in the 1990's I needed a new carb for my truck, and the parts company thought, all 1981 carbs that were feedback would work with all 1981's that needed a feedback carbs. They were wrong. there were two different calibration codes and I kept getting the wrong carb. etc.

 

Is there anything on my distibutor that would give me a clue as to the right carb for calibration purposes?

 

I think you got mixed up. The feedback carb system with the computer does not have a vacuum advance line. I was reading some of the earlier posts, and heard some of the guys where hooking the retro-fitted distributors to the egr vacuum port on the feedback carb. Thinking about it, this is their only option, since that wil be the only ported vacuum source on their computer setup. I would consider this temporary though, till a new carb is found.

I would not get hung up on what carb to get. As long as it's not some weird california calibrated carb, I believe all of them that were made for a 300 six, and had a duraspark II ignition, would work. To be safe, stay with a 1980 or lower year. I don't know when they went to the computer/carb on the six, but it was in the early eighties I believe.

 

1981 to 1983 4.9Ls with the MCU (microcomputer control unit) do have feedback carbs with a vacuum advance port and a slightly modified DSII system. Found in california and some High altitude models.

This is correct. And it won't run right until the carb is swapped.

Nope see the examples above. California, or some High altitude models.
It was in 1981 when Ford first started using feedback carbs and computers, "MCU" with a hybrid DSII ignition, on certain models. And by 1984 it went to the EECIV TFI-IV ignition.

Yes, to be safe, Stick with 1980 or earlier DSII, to be on the safe side. Then you shouldn't have a problem with calibration.