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I have recently become the proud owner of a Ford F150 1977 Custom Truck.
I love this truck and will be restoring it as a rolling restoration in the next few years.
My first problem: A very high fuel consumption (about 7-8 mpg) at 80% city driving (unloaded).
This is how the truck(ROY) is built:
- 400 cid engine
- 2 barrel Ford 2150 carburetor
- Automatic transmission (PJA BT1B7 D7TP ATA0 3345)
- Differential (WDM-BR 7BA 2.75 9 385A)
- Wheels Cooper Adventure A/T (31x10.50R15LT)
- Total weight: 4409 lbs
I have installed an AFR sensor. The AFR value at idle is 12.5, during various driving conditions between 13.5 and 15
All 8 spark plugs look good. I don't think the engine is running too rich.
What could be the reason for the high fuel consumption?
How high would you estimate the fuel consumption with this setup?
Assuming that your engine is in good shape and it's tuned up, 8-10 mpg is the norm for these trucks. There's not much you can do to improve it.
And welcome to the forums here on FTE. There are many good guys around with a ton of info and experience. This is THE place to find out any and everything about 73-79 Ford trucks. (At least I think so.) I've been a member here since 2004...and a dentside owner since 1987.
Welcome! Always great to see our overseas friends here.
Agreed with what was said above. You’re driving the wrong vehicle if you’re looking for good fuel economy. Have you put a vacuum gauge and a timing light on it to properly adjust the carburetor? It won’t get you much more in terms of fuel economy, but it can’t hurt.
Welcome to FTE! Boy, you guys in Germany with old Ford Trucks are growing in #'s! @patpat has a 79 F250 4x4 he bought from me, ya'll need to get a Ford truck meet going!
X3 on everything they said about mileage, 8-10 with a V8, my 77 F150/SB/4x4/351Measly/NP435/3.50's and 33's gets about 10-ish, my 77 F250/4x4/351Measly/NP435/4.10's w/33's gets about 8 maybe.. now if you go with a 300 6-cylinder you can get 18 mpg on the freeway, and usual town runnin around is 14-ish, my 79 F250, same specs as my 77 except the 300 avg. 18mpg over 1800 miles driving to MO when I sold it to my BIL.
I am the guy Pickupmanx2 is talking about. But I noticed that my name is not linked right. Probably my fault. Didn't think of the lack of letters you got over there and seems as there is another user with "patpat". I registered with which obviously turns also in patpat for you guys.. Damn!
X2 that those guys here in the FTE are an enormous help!
Where do you come from Whity_71? Do you know if your truck comes from California ?
Yes it does come from CA... I thought it looked familiar!! It was on the trailer with your truck the Green Monster Pat!! So it has the same amount of "sea miles" as yours!
What are the chances of that! Both trucks on the same car hauler heading to Germany. Nice looking truck.
I have a 400 in my 78 bronco, I get 7-8mpg. I will be rebuilding the carb trying to lean it out a little, and possible getting a little more mechanical advance from my distributor. But ya--these trucks don't do very well. The 460 in my 79 F250 gives slightly better at about 8-9mpg.
BTW - for a 2wd c/6 1/2 ton truck with a 400 i would expect more like 10-12...if not a touch better with a proper tune-up on a healthy engine.
X2...the 400 in my 79 consistently got 10mpg. I kept it tuned and it was mildly built, nothing crazy. Had an RV cam, headers, Edelbrock Performer intake topped with a Carter 625. Ran like a Swiss watch. I did run a Eddie 750 for a short time and didn't notice any improvement in giddy up n go or a change in fuel consumption so I kept the 625.
The AFR at idle is a little rich, so might just need a slight adjustment on mixture screws, that's assuming the AFR of 12.5 is engine fully warmed up and choke completely open. Your AFR while driving looks good though considering 14.7 is "perfect" stociometric ratio so I wouldn't mess with carb too much.
Might check base and total timing, mine seems to run best around 12 degrees advanced at the base with a nice mechanical advance curve up to about 34 degrees advanced around 2500 RPM. I would make certain your vacuum advance is functioning to. That can help low load efficiency by adding a bunch of advance when cruising and throttle plates are barely open/manifold vacuum is high.
I noticed you mentioned you have 31 x 10.50 tires, stock tires were 235/75-15 which are around 28" tall, those extra few inches of tire height combined with 2.75:1 rear gears your engine may be struggling to get that weight moving. Those taller tires effectively changes your gear ratio to 2.48:1, great for highway speeds and keeping RPM down, but makes it more difficult to get truck moving thus using more fuel to do so.
Dropping down to a 28" tall tire or replacing rear gears with 3.00:1 might help.
Also, if the speedometer gear wasn't changed to account for change in tire size you might not be calculating your fuel consumption correctly since the speedometer is off and how many miles you actually traveled won't match what the odometer says you traveled.
All that said, 10 mpg give or take a couple points is the norm for these trucks in my experience.
Another thought popped into my head, with current setup of tires and gears, at 65 mph you'll be sitting around 2000 RPM which is nice on engine wear, but the factory mechanical advance curve with stiff spring on the advance weight often keeps full mechanical advance from occurring until 3000 RPM or so. Since you'll be sitting around 2000 RPM at highway speed, you might not be getting much mechanical advance at all. Going to a lighter spring on the advance weight inside distributor will help reduce the RPM required to get full advance. It would be a good idea to check what RPM you have to hit to get full advance and make adjustments as needed. You can get lighter springs to "tune" the advance curve.
I don't have the website handy but @KubotaOrange76 I think is who provided me with a website that has pictures and instructions how to recurve your dizzy. Unless you want to shell some money and buy a custom curved dizzy. I have more time than money so I prefer DIY solutions whenever possible.
mterickson brought up one thing I was thinking while reading your story. With the tall tires and the 2.75 gears you may be struggling to get the truck moving if you're primarily doing city stop and go driving. In doing so you may be pressing on the gas pedal too hard which is gobbling fuel. It may sound counterintuitive, but a lower gear (say a 3.25 or so) may actually give you better economy.
Also, as mentioned, if your speedo is reading low because of the big tires, it may not be recording all the miles you're driving and you're thinking 8 when you really might be getting 10, which is still in the range of normal for a 400.
So it has the same amount of "sea miles" as yours!
But I noticed that my name is not linked right. Probably my fault. Didn't think of the lack of letters you got over there and seems as there is another user with "patpat". I registered with
