Help me identify why my mileage sucks....

Discussion in 'General Tech' started by Mace, Feb 18, 2009.

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  1. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    1984 FJ60 with a 89 5.0 mustang HO motor that is mildly massaged (69 351heads and a fairly fat cam)/C6/203/Stock tcase.

    4.11's 35's

    I get about 11 mpg with this setup.

    doesn't really matter what I do, I get about 11 mpg, highway, in town, pussyfooting it, enjoying the motor, etc..

    It passes smog with flying colors. No codes thrown, almost everything is brand new in this motor including the O2 sensors. Timing is set to ~13 IIRC (or whatever stock is supposed to be)

    These motors in a car got up to 28 mpg (verified) while out on the highway.. I would love to see 16 or 18..

    All of the smog stuff is intact. And will remain there. the actual air pump was supposed to route into the heads. I have it set up to inject into the exhaust. upstream of the PS O2 sensor. I am wondering if this is one of the problems. Perhaps the O2 sensor is getting too much air and making the engine run overly fat (does not really seem to be but). I just have a hard time thinking it is the problem because the motor is designed to run this way....


    Is the C6 that much of a gas hog? No overdrive or lockup could be the issue I guess. I could swap it out to a AOD. That would not be too tough to find. But I would hate to swap out a fairly bulletproof tranny for one that will need a lot of love to be anywhere close to as strong..

    :bang:
     
  2. Gumby

    Gumby Supamod Staff Member s-Moderator

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    I have no problem seeing a 60 with a massaged 5.0 with a non OD trans getting low teens. It's a heavy brick. I doubt any one is getting in the 20s with the axle gearing the 60 has. Are you pushing heavy tires or expedition equipment like racks, and a lot of extra weight?

    An AOD would help, but it's a crap trans.


    Can you get block learn numbers or even O2 numbers out of that EFI?
     
  3. cruiser88

    cruiser88 SILVER Star

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    Yep. You mean the metric tranny? Freak he would have to change everything.:eek:
     
  4. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    35" BFG AT's so the tires are not huge heavy. Not small by any means but they are not 35" swampers..

    The massaged portion I would expect in stop and go traffic, but there is no reason it sould be hitting so hard on the highway, at least I would not expect it.

    bob is pretty lean all things considered. A small thule rack on the top is about it, Front bumper is a skeleton and the rear bumper is non existant right now..

    AOD is the Ford non computer controled automatic tranny..

    To be truly odd I could just do a 700r4 ;)

    Bout the best I could do for a computer hookup is put one of the summit gauges directly off the O2 sensors..
    Perhaps compare the two

    Only one has the air pump to it..
    the differences in readings could be significant.
     
  5. Gumby

    Gumby Supamod Staff Member s-Moderator

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    I could be way off here 'cause I'm talking out of my ass with Fords, but...

    5.8 heads on a 5.0 would mean bigger valves and bigger ports which would translate into lower volumetric efficiency at lower engine speeds.
     
  6. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    Perhaps, but doing almost 50 mph in first gear is fun ;)
     
  7. Gumby

    Gumby Supamod Staff Member s-Moderator

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    I suspect that's true, but both would contribute to bad fuel mileage.:)


    You could do what I do and just try to not pay attention to fuel mileage on my toys.
     
  8. splitshot

    splitshot Head cook, Bottle washer, and Peace keeper. SILVER Star

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  9. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    hey, anyone happen to know what the spline count of a 4x4 AOD is?

    4r70W??
     
  10. Gumby

    Gumby Supamod Staff Member s-Moderator

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    I've got an AOD on the floor of the shop, but it's 2wd. Want me to check anyway.

    No 4th gear. Really common with those.
     
  11. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    AOD stood for Automatic OverDrive..

    And it is a three speed?

    I found a 2003 Excursion tranny and Tcase at the Junkyard for $100 today. It was surprisingly small..

    I need to figure out if that tranny would bolt to my 302 and what it would take to work..
     
  12. lingo

    lingo

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    Excursion probably had a 4r100 in it. It wouldn't bolt to a 302. You could get an EOD (early 4r70) and your ECU should be able to run it with a reflash. I don't know that you are going to get much more than 11 mpg out of that truck though.
     
  13. Gumby

    Gumby Supamod Staff Member s-Moderator

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    no, no. 4th gear is out of it. Any AOD is a four speed, but they had a number of problems with the 4th gear actuation. Most common was the 4th gear band blowing out. When I took this one apart the 4th gear band was good, but it just shifted into nothing when it hit 4th, so something was bad. They also were notorious for the rubber check balls to break down.

    An E4OD is a better trans. I don't know what would need to be done to run it, though. Still ain't a great trans.

    I think I'd sacrifice mileage for reliability. In fact, I do. I run a TH400. One of the biggest power sucking transmissions out there.
     
  14. John Smith

    John Smith In the garage

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    I think it is a combo of the 35s and your gears, along with a higher rig height making it more of a aerodynamic brick than it was. I noticed a big mileage decrease when I went from 33s SUA on my 40 to 36s SOA in my 40.
     
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