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Old 04-29-2009, 12:07   #1 (permalink)
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Bad gas mileage

hello. i just got my 302 all rebuilt and dropped it in my 1984 f-250. the motor is a 1980 and it was removed from my old truck which was a 73 f100. the motor got great gas mileage when it was in the f100 but now that it is in the 250 it is gettin real bad gas mileage. i put new pistons rings bearings and timing chain in it with all new gaskets and it seriously took half a tank of gas with the driving i have done within the past two days which is not alot approximetly 30 miles. the truck has a 20 gallon tank. so thats coming out to 3 miles per gallon i can seriously watch the gauge go down. i had better gas mileage with the 351w. is there any explanation for this. the gear ratio in the 250 is 3.50 and the f-100 is 3.50 so it cant be that. also the tranny in the f100 was a toploaded 3 speed and i have a t-18 in the 250, so they are simliar except first low in the t-18. i have the motor timed 8 degrees before top dead center and it runs good. could it possibly be that because i rebuilt the motor it will take awhile for everything to work to together and maybe ill get better gas mileage say 500 miles from now? do motors use more gas during the break in period?
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Old 04-29-2009, 16:40   #2 (permalink)
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Re: Bad gas mileage

I'd get the engine properly tuned in with the computer. It'll run you around $500 for RWD and a basic, custom tune but it'll save you ten times that amount in fuel at 3mpg!

Search around in your area for a specialty shop with a dyno, most dyno shops will be able to tune your vehicle. I suspect this would be a good place to start, if not the last place you'll need!
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Old 04-29-2009, 17:20   #3 (permalink)
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Re: Bad gas mileage

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Originally Posted by 360ci View Post
I'd get the engine properly tuned in with the computer. It'll run you around $500 for RWD and a basic, custom tune but it'll save you ten times that amount in fuel at 3mpg!

Search around in your area for a specialty shop with a dyno, most dyno shops will be able to tune your vehicle. I suspect this would be a good place to start, if not the last place you'll need!
That would be alright on a late model, but a 84? Not much to tune.
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Old 04-29-2009, 17:37   #4 (permalink)
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Re: Bad gas mileage

True.

Perhaps plugs aren't gaped correctly, or they're worn? I forgot how hard it is to diagnose engine problems without have the idiot light!
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Old 04-29-2009, 21:17   #5 (permalink)
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Re: Bad gas mileage

i bought new plugs for it and gapped them at .035. yeah on this there is not much to hook to a computer. i have a points distributor on it that came off of a 78 granada. the thing that gets me is how it ran great in the old truck before i had to rebuild it and now that it is rebuilt it is getting bad gas mileage. another thing i noticed. maybe it could be my ignition curve perhaps. because off idle it has good acceleration but from about 55 on up it feels like you have to mash on it to get it to go. is there any way i can change the curve on a stock ford distributor? any advice is greatly appreciated.
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Old 05-01-2009, 20:30   #6 (permalink)
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Re: Bad gas mileage

i knew there was a problem at 3 miles per gallon jeeze i could be running a top fuel dragster and get better mileage. i was not familiar with this carb but right under neath were the accelerator pump there is a small vacuum port. needless to say this hole was not plugged or hooked up. so far with about 30 miles on a full tank it has not moved yet, thank god. looks asthought i should have examined the carb a tad more before throwing it on.
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Old 05-02-2009, 14:53   #7 (permalink)
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Re: Bad gas mileage

You should also consider how you're measuring miles. That old odometer may not be quite as accurate as it was when it rolled off the assembly line. Do you have a GPS you can test it against? If nothing else, you can use the mile markers on the highway.
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