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Thread: Fuel mileage questions

  1. Top Of Page | #1
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    Fuel mileage questions

    Hey everybody this is my first post here. I am looking for some knowledge.
    I recently swapped a 92 12 valve into my 2001 f350 6 speed 4x4. Prior to pulling the 12 valve out of the dodge (auto, 2wd) it was getting a respectable 26 mpg. This was in November so the temps weren't super low yet and I am pretty sure the fuel at the pump was winterized already. As far as I know the engine was a 1 owner older gentleman and is bone stock. It had 330000 KILOMETERS on it
    Now the swap is completed and fummins is now on the road but getting only about 15 mpg. The temps are wicked cold right now. Truck fires up Instantly and runs pretty good. For the first few minutes it will fart a bit when I rev it. But it always seems to have some blue smoke. My thought is injectors. If they are original they could be getting tired and leaking a bit? Anyway I have ordered new injectors to install and just wondering if maybe there is something else I should be looking at as well. I plan on keeping the engine stock I don't give a rats @$$ about stop light racing or pumping black smoke everywhere.
    any advice is much appreciated.


  2. Top Of Page | #2
    WE WILL STAND! IGOTACUMMINS's Avatar

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    Sounds like the injectors are leaking a bit and with it being so cold out that doesn't really help fuel mileage that's for sure.

    Also welcome.

    "The grass is greener where you water it"


  3. Top Of Page | #3
    Old & Grumpy! Polaraco's Avatar

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    As soon as anyone says MPG they think of me. I'm the MPG hound and agree with you.

    I assume your complaint is you lost 10 Mpg. Yeah I'd be complaining too. What's the difference in the rear ratios and did you go from a 2WD to a 4WD?

    At 330K Kil, they may just need a good cleaning. Try throwing a couple of cans of Sea Foam in the tank and see if it improves. I have a similar prob on my 03 and tried a fuel additive made by Archoil. (There's a thread on it running) Cleared up everything instantly. People are skeptical, don't blame them. But I have to say my problem just disappeared in like 10 minutes. Like a magic wand.

    Injectors are cheap for those old 12 valves and allot less problematic. But for the price, the sea foam is a cheap try and the archoil might work for you, and it might not. I was impressed with it


    2003- 3500 RWD Automatic.
    S & B intake, BD Intercooler, Pusher Air Horn, MM3 Double R Tuning, Turbo Timer, electric Flex-a-lite fans, FASS 95,
    50 HP tips, upgrade to 351 turbo, 3.42 gears, Twin air compressors, air bags, Remote dual oil filters, Hellwig sway bar, Front Winch. Home made Fuel Heater, BD Exhaust brake with Torque Lock. Tons of TLC

  4. Top Of Page | #4
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    The dodge was a 2wd auto the ford is a 4x4 manual. The extra 1500 lbs or whatever it is shouldn't make that big of a mpg difference to an engine that is factory rated for 66000 I would think. I revs at about 1800 rpm at 105 kph which is a bit lower at highway speed than when the engine was in the dodge.


  5. Top Of Page | #5
    Old & Grumpy! Polaraco's Avatar

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    Which is lower. The Speed or RPM


    2003- 3500 RWD Automatic.
    S & B intake, BD Intercooler, Pusher Air Horn, MM3 Double R Tuning, Turbo Timer, electric Flex-a-lite fans, FASS 95,
    50 HP tips, upgrade to 351 turbo, 3.42 gears, Twin air compressors, air bags, Remote dual oil filters, Hellwig sway bar, Front Winch. Home made Fuel Heater, BD Exhaust brake with Torque Lock. Tons of TLC

  6. Top Of Page | #6
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    Quote Originally Posted by Polaraco View Post
    Which is lower. The Speed or RPM
    The rpms are a slight bit lower on the highway. I figure 1800 rpms is good for highway travel


  7. Top Of Page | #7
    Old & Grumpy! Polaraco's Avatar

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    I dunno man. clean the injectors with the sea foam and see if there was an imporvement


    2003- 3500 RWD Automatic.
    S & B intake, BD Intercooler, Pusher Air Horn, MM3 Double R Tuning, Turbo Timer, electric Flex-a-lite fans, FASS 95,
    50 HP tips, upgrade to 351 turbo, 3.42 gears, Twin air compressors, air bags, Remote dual oil filters, Hellwig sway bar, Front Winch. Home made Fuel Heater, BD Exhaust brake with Torque Lock. Tons of TLC

  8. Top Of Page | #8
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    With it being 4x4 that's were your milage went. You have to rember that even though your not in 4wd that you are turning a extra axle transfer case and drive shaft. Are the hubs locked in that will cause low milage also. What gears are in the axles that could cause some milage loss as well. The popping at cold start could be that its not getting enough fuel till it warms up a bit. Diesel is oil and it takes a couple minutes to thin out. Is your grid heater working it could be that the air is just too cold to complete the cumbustion cycle.


  9. Top Of Page | #9
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    Um aside from the extra weight of the 4x4 system there are no extra moving parts when I am in 2 wd. The front axle is manual hubs which are set to free spin when not needed and the transfer case is disengaged when in 2 wd. Grid heater is wired to a push button for start up. So it does not automatically come on when the air temp is cold such as it would in the factory set up. So yes that could have some effect when the air is really cold, but 10 mpg? I am proactively going to change the injectors this truck goes to the yukon and back so the last thing I need is for a breakdown up in the middle of nowhere.


  10. Top Of Page | #10
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    And I am pretty sure I have the 3:73 axles. My tires are 285's and they turn 1800 rpm at highway speed. If they were 4:10'a it would be much higher I assume


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