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  1. #1
    Bobtail Member
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    Detroit 14L Mileage

    Hi Folks!
    My dad drives a 2007 Freightliner Century Detroit 14l (2006 engine) and it is giving him poor mileage, somewhere to the tune of 4 mpgs. I've done the barometric pressure modification, and it did nothing to increase the mileage of the truck (This mod sets egr to low setting by way of telling the ecu it is at a certain elevation). Any input on what could be wrong? We have no air leaks that we can sense and the dash reads 4.70 mpg plus a tenth or two. It is 10 speed also. Also, what are you guys with 14L Detroits getting for mileage? Any tips would greatly be appreciated.


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    I am running around 5.8-6.4 right now.

    Use windex or some kind of a soap spray and spray your intake side from the turbo all the way to the intake manifold. You'll want to set the idle up to 1000 rpm when you do that.

    At what speed is he running at both engine and road speed when he's cruising.

  3. #3
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    I typically get from 5.5 to 5.7 with mine. 2007 14l with a 10 spd. I pull fairly light loads but enough wind resistance to more than make up for less weight.

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    should have mentioned.

    I drive an 07 Century, 14L EGR, 13 spd, 3.42 rears.

    It's also been tuned by Rebel127.
    Attached Files Attached Files

  5. #5
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    I will ask him tomorrow. Right now he is sleeping. I've searched the net for a few months now and a lot of people are experiencing a 4xx mileage problem from this engine. I will check with Windex. If it is leaking, could this cause a 1MPG drop in mileage? Also, how much for your tune and what were your mpg gains?
    Thanks MNdriver.

  6. #6
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    Talk to Rebel about cost. I made a special deal with him and let him do testing with my truck on a dyno.

    I can't really say on the mileage. I did it in Dec and been dealing with winter weather/fuel since then. I am getting about the same in the winter as I was late fall so I am guessing it will likely be 1-1.5 mpg once summer time comes around again.


    Also, when was the overhead ran on that engine last? If it's been over 150-180K miles, get it done.

  7. #7
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    MNdriver is rite about the over head I have seen to many detroits that have not head the overhead in a while, and the intakes are often way to tight. Is there any codes?

  8. #8
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    Yes. 1 code that is intermittent when the gas pedal is applied at highway speed. Had it checked and tech couldn't find nothing. Definitely going to get it checked out by a different dealer this time (Freightliner this time).

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    Do you know what the code was?

  10. #10
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    No I don't. I can check tomorrow. I want to help the Detroit guys on this one. I am gonna spend the money to get this problem fixed.

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