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Discussion Starter #1 (Edited)
I've been fighting the crappy gas mileage demon with my 460 powered '89 F-350 for a while now, but today was the last straw. I had already done a ton of tune-up type work plus a few things that shouldn't make any difference. The list includes: fixed exhaust leak (new manifold gaskets), new muffler, new O2 sensor, new fluids for everything that uses fluid, new EGR valve (check engine light code indicated problem there), new filters everywhere, new plugs/wires/cap/rotor, cleaned injectors (sea foam), and a few other things I'm having a hard time remembering. Oh yeah, compression readings were 125, 124, 125, 125, 122, 124, 118, 122. I finally gave up and took it to a real mechanic today and paid them to tell me that there is absolutely nothing wrong. He scanned the computer, checked the fuel pressure, tested the O2, measured backpressure, looked for vacuum leaks, and whatever else he could think of. The end result is that the truck still gets 3.6 MPG! This is in a dually cab-n-chassis with a dump bed so I don't expect great mileage, but 3.6 when driven like a granny is just rediculous!

So, why am I going to hell? I'm considering dumping the Ford motor entirely and dropping in the TBI Chevy 350 that's currently powering my buggy. It makes more power than the 460 and couldn't possibly burn as much gas. Anybody ever done this? Am I just asking for more problems than I'll solve? Any comments or suggestions are welcome.
 

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Debauchery Wizard
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by the time you get all that done, you will be into the project a few hundred bucks(likely more),still getting relatively crappy gas mileage AND out a buggy. go on craigslist and buy a 4 cylinder beater to putt around in.
 

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4mpg?

you have no overdrive and 5.13 gears on stock tires?
 

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The end result is that the truck still gets 3.6 MPG!
You are doing something way wrong. I get 4-6mpg and thats with a stroked out 600hp+ 460, 44" tires, 950cfm doublepumper race carb, one tone parasitic axles and a retard with a heavy foot.
 

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when your actually driving 60 your speedo must be reading 45-50...do you get pulled over alot?


i would swap in a cummins first, or a good 6.9 7.3 idi or a 6.2/6.5 with a banks turbo if you cant find a cummins cheap.

honestly the 350 is an easy swap as you already have it and the 460 should be fun in the buggy.

i see it as cost effective to run what you got...swap em out. i know what it would take for me to do that and it would pay for itself in a month or two easily...i assume you need the truck to work out of naturally or would not be driving it.
 

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Discussion Starter #6 (Edited)
Assumptions above are correct. I need this truck as a work truck hauling gravel and concrete blocks for building retaining walls. I also haul a lot of trash to the landfill. The truck only moves when it's making money; my '94 geo Prism does all the non-loaded miles. The truck has no overdrive with the C-6 tranny and the gears are 4:10. Stock 31 inch tires. I don't think I've ever got up to 60 MPH. I usually piss a few people off doing 45 in a 55 zone trying to stretch my MPGs, for what little good it's doing.
 

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Every newer 460 I've been around has picked up mileage with a better exhaust, a "high flow" cat and a 3" single pipe with a good low restriction muffler should help a bit. FWIW my old work van(94 e-350 w/460 and 16' box) got 4-5 mpg, my new van(03 e-450 w/v-10 and 15' box) gets 7-8mpg, if the truck is a work truck just pass the cost down to the customer.

Brewchief:D
 

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You say that you replaced the cap, rotor and wires right? Did you check your timing and check to see if the advance was coming on at the right time?
 

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for a heavy truck i can see that. your rig must be over 7k unloaded - with no overdrive ( its the lock up converter that helps - no slip ) and is under load all the time. i had a 89 f250 with a 7.5-c6 - 3.55 and it got 7-8 unloaded - with a best of 10 - add a few thousand pounds, heavy loads and presto - its gallons per mile, not the other way


i have worked on a few 7.5 motor homes that average 5-6 mpg - and they dont pull the load like you are - if you want better go oil burner

- but dont expect huge # there eather - our 02-04 f650 with a 5.9, allison, 4.88 and 34" tires ( lo pro 22.5) unloaded could bearly muster 7 mpg -
 

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As mentioned above look for an exhaust restriction. My 78 F250 (RIP) w/460 went from 9 mpg with my welding rig (about 1800 lbs) to 13 mpg when I installed headers and 2 1/2" exhaust all the way back. This included cats as I had to pass emissions at the time.

I realize you are much heavier than I was.

This past March I used my current truck, 93 f350 4x 7.3 IDI NA E4OD 3.55 gears and 34" tires to pull my gooseneck which weighs about 4k plus 9k in equipment from Houston Tx to Lynchburg Va. Total weight with truck was over 20k. I averaged 10 mpg. I could not pull it in OD so with the exception of the lockup converter I was essentially in the same boat gear wise as a c6 would be. Same truck empty gets 20 mpg if I am easy on it. 18 if not.

Is your tranny slipping possibly?
 

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Instead of swapping engines, swap trannys. I think a ZF would help things out a lot. 3.6mpg is horrid, our 2-ton trucks with gassers don't even get that bad fully loaded.

FWIW, my '88 f-250 ex cab long bed 460/ZF/1356 (w/ good intake and exhaust) 3.55 gears, 33" tires gets 13mpg empty on the highway and around 9mpg towing 10,000lbs. I think you have something major going on other than the engine.
 

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Gees, I got 7.5 towing 9000 lbs on my 95 F250, 7.5, E4OD, 4WD, ext cab, long bed. Best I got highway was 12.5. I'm not sure what I could have done to it to get 4 MPG??????? It was 6345 curb weight BTW.............
 

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How much does it weigh loaded? Also if you think that a TBI 350 in a buggy that weighs little to nothing has more power than that 460 and will get better gas milage pulling that heavy truck around go ahead and do the swap and report back to us. I think you will be suprised to find that if the 460 is right and I mean no codes and running the way its suposed to that it might get better milage depending on the weight your pulling and I know the 460 will have more grunt. Like mentioned before the cats on the older EFI 460s were bad about pluging up, also the ECMS on the early EFIs had some tunning isues that lead to poor milage. Ford had an updated ECM that helped alot. I have a friend that had a 89 crewcab dully that he changed the ECM on for just this reason and he clamed his milage doubbled. He said he went from 4mpg to 8mpg.:D
Leadmic
 

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Your compression is a little low, and I would venture a guess that you have a slipped timing chain to warrant such atrocious mileage. My dad's old '86 F-350 got 8 mpg loaded or not, and my buddy's '93 4x4 F-350 gets around 10 unloaded. I'm inclined to go towards some major valvetrain issues to cause anemic performance like that.

When the chain slips a tooth it retards the cam timing by something like 6* IIRC which can play hell with your cruising RPM mileage. Unfortunately, the only way to really be certain is to degree wheel the thing, and by the time you get it apart you'd be better off pulling the motor and rebuilding it.

Oh yeah the TBI Chevy is going get even worse mileage in that application. Plus Chevy engines in Fords = gay.
 

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4MPG on a dump truck, with I'd guess 8-10k in it (if your hauling cete' ) sounds normal to me........
 

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4MPG on a dump truck, with I'd guess 8-10k in it (if your hauling cete' ) sounds normal to me........
Our 1975 C60 loaded to 28,000lbs gross gets 5mpg, there's definitely something wrong here. I'm still betting on the tranny.
 
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