Tunes, parts and Mpg

DISTURBED

DISTURBED

YEA WE RIDE THE SHORT BUS
So I have this 07.5 that I've been fight a rail pressure code issue. I have changed almost every thing in the fuel system for different parts and it still sets the low rail pressure and low lift pump codes daily. Something I have noticed was when the truck had the original 400k mile parts on it, I would get 18-19 mpg on the highway just the truck by itself. So as I've switched the injectors, cp3, rail plug, ect. I'm now down to 13-14 mpg highway. I've not changed the tune and fuel pressure is 14-15 psi which FASS says is fine. Anyone else ever had this drastic of a drop by swapping stock parts for stock parts?
 
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Yes,rail plug is leaking under higher pressures. Sand the rail plug flat and install a copper washer under it then crank it down
 
Have you checked the FCA harness? Mine was setting high rail pressure, and was commanding 100% due to an internal wire problem. Might be worth the $17 for the replacement piece.
 
06 DIESEL said:
Have you checked the FCA harness? Mine was setting high rail pressure, and was commanding 100% due to an internal wire problem. Might be worth the $17 for the replacement piece.
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I've got a gauge for the rail and it builds 21-22k cold and as soon as it warms up it will start setting the low supply pump and low rail code. It will drop to 19k and under a hard pull 16-17k. I can live with the low rail code but finding the issue would be nice. I'm more curious about the loss of mpg. Truck has way more power after swapping parts but the economy has gone down.
 
I’m curious about the plug and/or connecting tubes.


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I've had that happen it's several things. Old injectors were worn and injecting more or less fuel than stock. PRV may be malfunctioning letting pressure by. and then Fuel pressure sensor has been found to cause havoc! Is the truck defueling when the CEL comes on?
 
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dangerous06 said:
I've had that happen it's several things. Old injectors were worn and injecting more or less fuel than stock. PRV may be malfunctioning letting pressure by. and then Fuel pressure sensor has been found to cause havoc! Is the truck defueling when the CEL comes on?
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No it doesn't defuel. All I've noticed is a little power loss and the rail guage shows less psi then it did before it set the code.
 
This sounds like aerated fuel to me. Does it always start like it should?



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I assume new CP3. And the return banjo on the back of the head? But like Biggy said if it's sucking air that would cause it but I'm sure your gonna say it has a sump! So maybe do a bucket test on the returnsee if it's aerated.
 
dangerous06 said:
I assume new CP3. And the return banjo on the back of the head? But like Biggy said if it's sucking air that would cause it but I'm sure your gonna say it has a sump! So maybe do a bucket test on the returnsee if it's aerated.
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You have to be careful looking at the return side for aeration. Beer Head = OK

Big bubbles not ok

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