Bad Fuel Mileage has developed - Ford Powerstroke Diesel Forum
 
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post #1 of 8 Old 08-24-2019, 08:09 AM Thread Starter
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Bad Fuel Mileage has developed

Will give a small introduction to what truck is before asking questions.

Early 99 model 7.3l
Has 5" exhaust to rear axle. Then narrows down to 4"over rear end.
Banks waste gate
Edge evolution programmer
Wicked2 turbo wheel
Cold air intake


Truck used to run around 18mpg no matter what. Pulling a heavy gooseneck trailer I would see 17 still.
Truck had a transmission rebuild and in that time truck set for a couple weeks.

Got truck back and mpg has been terrible. Around 300 miles to a tank.(8-9 mpg)

Not getting any codes that mean much. Getting one for back pressure valve. But it was removed so I know why it pulls that.

Truck went to shop and was told gasket on turbo pipes need replaced. Did that and still getting terrible mileage. Hate to throw dollars at it in a shop and hoping to get lucky.

Synotom that has started without any warning or pattern. I can pull up to a stop light. The check engine light kick on. Light turn green and try to accelerate. Truck will sit and idle no matter how much pedal input given. Can last a couple seconds to say around 10 seconds. Which might as well be an eternity when cars behind you. Check engine light goes and then the lightest input to throttle will launch truck like I am coming off the line at a dragstrip. It will keep going like a runaway. Let of pedal and return to same input and truck goes back to normal. Once CEL goes out there is no code left to scan.
I don't know if that has anything to do with MPG drop but it has developed around same time mileage has went down the drain.

I know it is likely many things but maybe some ideas or input from more knowledgeable people will help diagnose or give me same input shop is doing right now and throwing ideas at it.

Being told ICP Sensor should be looked at or have a possible bad turbo. Again trying to keep from throwing money.
Thanks for any help.
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post #2 of 8 Old 08-24-2019, 09:33 AM
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Check for a dragging caliper maybe?
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post #3 of 8 Old 08-24-2019, 11:00 AM
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Just asking - could it be the trans needs to break-in? Just going by you saying MPG was good before, not so after.


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post #4 of 8 Old 08-24-2019, 01:10 PM Thread Starter
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I have checked over little things for drag or anything of that nature.

I also don't think transmission would be needing break in time but I could be wrong.
Transmission rebuild was a bit of a fiasco as I had a person who swore they could do it mess things up. Trans went out guy messed trans mission up and ruined the case. He plugged into computer with a fancier scanner and was watching truck call for gear and of course trans wasn't shifting. Took truck to someone I could trust to rebuild trans. Found out he twisted case and ruined parts of the internals. I found a core in salvage and had it rebuilt by reputable trans builder and installed. One thing in back of my mind is possibly different internal gears in transmissions? Truck has been out of shop since winter after rebuild. Mpg has been done since then. Just was hoping something would fail so I knew what to fix then. No luck just terrible mpg since then.
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post #5 of 8 Old 08-24-2019, 01:47 PM
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Are those hand calculated numbers or going off of the display? 17 mpg pulling a heavy gooseneck is unheard of, unless your going off of the digital display which is not accurate.

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post #6 of 8 Old 08-24-2019, 06:23 PM
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Bad Fuel Mileage has developed

Yeah thereís no way you were getting 17 mpg pulling a gooseneck, 14-16 unloaded is what is obtainable around town generally.
You can clean your exhaust back pressure sensor tube to see if that helps


Your other problem could be a couple things, first check your wiring over the drivers side valve cover to make sure it hasnít worn through anywhere. Probably not the problem but just make sure

I bet itís either your ICP sensor or IPR valve. The valve could be sticking and then freeing up, thus allowing you to move suddenly. It could also be your pedal position sensor, though ICP and IPR are far more common.

What would be best is to have a CTS monitor on your truck to watch these things as they happen to diagnose, but I would bet itís your IPR based upon your symptoms


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post #7 of 8 Old 08-25-2019, 05:45 AM
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dead pedal and check engine light indicates the TPS or IVS is faulty. You can take apart the pedal assembly to clean and re-calibrate. Being able to monitor while this is occurring would help. You want the IVS to close at around 0.8v and full throttle is anything above 3.8v. Sounds like your IVS is sticking and the TPS is out of calibration.
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post #8 of 8 Old 08-25-2019, 08:51 AM Thread Starter
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My old truck doesn't have fancy digital readings. It is all hand calculated. And I assure you I was getting 16.8-17.2 mpg pulling my enclosed gooseneck trailer. Maybe I had a unicorn truck that got awesome mileage. Regardless I have been spoiled by it and now it hurts filling truck up twice as often.
I pulled connector off ICP Sensor and there wasn't any oil on connector.(was told that was a tell tell sign it was bad)
Going to check all pipes for leaks or cracks in tubes. Gonna check over simple stuff and guess take it in to another diesel shop that will have to scanners needed to diagnose.
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