Well, today I checked the timing for the first time on my '86 4.9L with stock EEC-IV and feedback carburetor. With Spout disconnected, ignition was right at 10 degrees BTDC. With Spout connected, timing advanced to ~ 16 degrees BTDC at idle. Increasing engine speed up to 2000RPM advanced the timing off the scale. Overall the timing advance was completely responsive to engine speed, and always returned to the same spot at idle.

So my system appears to be fully functional, and my computer codes are all "System Pass". Knock on wood, I seem have a complete and working stock EEC-IV feedback carbureted truck! Last of the Thick-Film Interceptors . I'm getting right around 20 miles per gallon (4 speed overdrive, 3.08 rear, and size 235 tires).

 

That is very impressive I must say! I have a 5 speed with 245 tires, and I believe 3.25 rear and I get 13 or less in my 4x2 1995 dodge. Super jealous!

 

Well I drive like a grandma and coast whenever possible. That probably has more influence on mpg than just about anything else.

 

I have always stated that a properly functioning feedback system on the 300 will give the best MPG, especially when combined with the 4 OD trans and around 3.00 rear axle ratio. Even the best tuned DS2/non-feedback carb combo will fall a little shy of matching the feedback system in proper working order.

 

Hey Galendor,
20MPG is great for a 25 year old full size 4X4 pickup. As you know our trucks are similar (aside from mine being 2WD) and I am getting about 15-16.
I did finally get mine up to 70MPH for the first time since I bought it. I had to take my daughter to a birthday party and got to take her on a paved rural highway. It really surprised me, I looked down at the speedo and I was doing 70. Not being on gravel or in town was probably a shock to the old girl.
Sorry to highjack your thread.
Congrats on the mileage I am jealous.

 

Hi Erik,

Our trucks are even more similar than you thought - since mine is also a 2WD. 2WD, short wheel base. So that probably contributes to my good gas mileage, as does new motorcraft plugs, wires, battery, air filter, etc. Also I don't carry a bunch of junk around in the truck, just a minimal tool set. Good job getting up to 70 - one good thing about the highway gearing is that in OD, my engine is only doing 1500 rpm at 70mph!

I also replaced my wheel bearings, replaced all my engine belts, adjusted their tension very carefully, and waxed my cooling fan blades! All these little things probably contribute to good gas mileage.

 

I could have sworn your truck was a 4X4. Obviously I was up in the night on that one. I have to admit I do not do a very good job of keeping the bed as empty as I should. It typically has something or other in it.
Your truck is in a much better state of tune than mine is and with the EEC-IV system properly working I will never catch you in terms of mileage. I do not drive fast but probably never really get the truck in a position where it is cruising at the most economical speed.
Just out of curiosity how many miles do you have on your truck?

 

94,000 miles, one owner before me. I do kind of wish she was a 4X4, but frankly I wouldn't find much occasion to use it. My other vehicle is AWD for the rare snows here.

 

Galendor,
Our trucks sound like they are practically identical. My truck had 215 tires on it stock, which were promptly replaced with 255/60's once the originals were worn out. Now I have 31x10.5x15's on it, which I really like. Like you, I am getting about 20mpg/hwy. I am going camping this weekend and will check the gas mileage again. If you maintain the EEC-IV system they are very reliable and will get decent gas mileage, for what they are. Good luck with your truck.

 

Keep in mind this feedback system, along with the 4 speed OD and tall-ish rear gears were responsible for the EPA rated 30 MPG advertised back in the 84-86 time frame.
Real world MPG was closer to 20-25 MPG. A number that still hasn't been matched by "modern" EFI and fully computerized engine controls.
The 300 was not dropped from the lineup due to poor MPG or reliability, it was dropped due to not fitting under the hood (and firewall) of the 97+ F150. That, and the fact they lasted too long. Hard to sell a man a new truck, when his older truck is still running perfect even with well over 200K miles on it.......
The switch to EFI on the 300 in 87 didn't really help the MPG compared to the feedback carb and computer ignition, but it did make the engine last even longer. Of course, there were also internal engine changes which improved the power/torque output, and they were partly the reason for the loss in the MPG with EFI. When you improve the airflow capability of an engine, the MPG tends to take a hit.
When the 4 speed OD was dropped in favor of the 5 speed, it also dropped the hiway MPG due to a lower OD ratio. The tallest rear gear ratio *I* have seen behind a 5 speed is 2.73. On the other hand, I've seen many 4 speed OD's backed by a 2.47 rear gear.

 

My hats off to you for getting feedback carb/TFI to run as intended!..........never been able to do it on 83-85 Ranger V-6s...........Great work!

The most "Awesome" thing I have ever been able to get about EEC feedback, was the distance I could toss the parts into the woods behind the house after durasparking it.

 

Good info Rogue, but how do I get that elusive 30mpg in my truck?

 

Same way the EPA did. Put it on rollers inside a building. The 30 MPG rating was done back when NOTHING was capable of actually hitting the EPA hyw estimate.
The revised EPA numbers are more in line with what you are currently getting. The EEC/FFS 4.9L with 4OD can get real MPG in the 20-25 range, depending on terrain and rear gearing, when it's all working correctly.

 

I believe my mileage sticker said 17-21 mpg when new.

 

Take a look at this ad from 1984. After watching it, pause at 0:19 and read the fine print. It says "Optional 4 speed shift" and goes on to add "Actual hyw mileage and california ratings lower"......

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