Terrible Fuel Mileage: 7-8 MPG No Matter What! - Ford Powerstroke Diesel Forum

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post #1 of 12 Old 07-18-2013, 11:55 AM Thread Starter
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Terrible Fuel Mileage: 7-8 MPG No Matter What!

Hello everyone,
First post here, after scouring forums I can't solve my problem so I hope I can find some help here! I drive my Dad's/Boss's 02 7.3 f250 4x4 single rear wheel auto w/ 130000 km(80000 miles). It has no mods and we have never owned a diesel truck prior to this one which we bought in spring 2012. Whether I'm towing my 13000 pound trailer or I'm driving empty I have never gotten better mpg than 8.9 per US gallon and have gotten as low as 6.7(can't even do more than 8 anymore) so, seriously wondering why we spent all that dough... It also doesn't seem to pull that thing very easily at all.
We brought it to a diesel shop last year. A few codes popped up(forget which ones) so they burned out the ebps tube and cleared the codes and ran it hard on the highway(unloaded) and no codes reappeared.
So, a list of info, problems and repair attempts:
Starts fine, Runs fine
No smoke, white or black
Power seems low... Idk. Haven't driven another one
Boost tested at 28 psi unloaded (high?) also tested at 12.5 psi max boost before ebps tube but the tests were done differently by different people and no change in power or fuel economy happened so I'm suspicious that one or both were done incorrectly
Losing oil but haven't noticed any leaks ever under the truck
4 times has lurched violently on slowing down (different problem?)
Changed fuel and air filter
Cleaned ebps tube
Tire pressure is good
No check engine light

Also, I have a very light foot, although I have to push it hard to get up to speed. I cruise at 100 km/h (60 mph) and I don't use fuel additive. Fuel economy doesn't change whether its -20C or plus 30C, empty or loaded.

We don't drive it like crazy so putting money into finding a problem nobody has any idea about is very hard. But, if we find the problem and fix it, I know it will soon pay for itself.
Help and suggestions would be very much appreciated!
Thanks, Jon

Last edited by JonSiemens; 07-18-2013 at 12:00 PM. Reason: Added info
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post #2 of 12 Old 07-23-2013, 04:54 PM Thread Starter
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Does anyone have any ideas?
Could it possibly be a fuel leak? I know I should be getting better fuel mileage, especially empty!
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post #3 of 12 Old 07-23-2013, 06:20 PM
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do a compresssion test, just had a guy come in and said his fuel milage was horrible and we did a test and one cylinder was low on compression and pulled the head and the piston was all chipped and cylinder walls were scored.
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post #4 of 12 Old 07-23-2013, 09:13 PM Thread Starter
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Thanks, will do! I'll post back here with the results
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post #5 of 12 Old 08-01-2013, 09:40 AM
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Try changing out your CPS with a motorcraft one, A failing CPS can cause a boatloat of weird erratic problems in the 7.3. Usually having to do with poor MPGs and bucking and or/dying
Theres several different "colored" CPSs but this is the one you want Genuine Ford 7.3L Diesel Cam Position Sensor (CPS) - Blue

Its a cheap alternative that may solve your problem before you start tearing it apart and throwing parts at it. Its such a common problem that 7.3 guys keep and extra spare in the glovebox to change on the side of the road

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post #6 of 12 Old 08-02-2013, 12:47 PM Thread Starter
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Thanks a lot, I'll try that! I hope it's something that simple!
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post #7 of 12 Old 08-02-2013, 02:38 PM
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How are you checking your mileage? Since you are showing Kilometers are you sure you are doing the conversion correct? Seems like boost that high, no smoke, normal power, that maybe everything is fine. Have you checked your odometer and made sure it is correct?

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You will get some axle wrap with a heavy trailer, I can feel it when towing my gooseneck with some heavy equipment. My Deavers will wrap enough to make the tires rub the front of the rear fender well if I give it too much throttle on aceleration.
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post #8 of 12 Old 08-02-2013, 07:50 PM Thread Starter
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I am confident that my calculations and conversions are correct. I haven't done an odometer check though, that's a good call, but judging by the speed of traffic my speedo is really close at least.
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post #9 of 12 Old 08-02-2013, 07:57 PM Thread Starter
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Oh, and I'm plugging in kilometres drivin and fuel filled into a mileage app which converts it into US mpg
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post #10 of 12 Old 08-02-2013, 08:53 PM
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Does it have a catalytic converter. It may be plugged. Also maybe your EBPV is stuck. Its the butterfly in the turbo outlet flange.

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