Does higher fuel pressure = less MPGs? - Ford Powerstroke Diesel Forum
 
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post #1 of 9 Old 01-25-2012, 11:03 AM Thread Starter
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Does higher fuel pressure = less MPGs?

So far all of my logic points to yes as well as my fuel gauge!

We all understand that the stock system needs at least ~55 psi of fuel pressure to function properly. Fuel pressure is maintained via the FPR spring. My brand new rebuilt FPR is currently at 72 psi. Whatever fuel is not returned through the FPR flows through the injectors at the given duty cycle.

So if the truck will run like its supposed to at 55psi of fuel pressure and I'm providing it 72psi of fuel pressure, that means that i'm forcing more fuel through the injector each duty cycle. I'm not exactly sure how much fuel the additional 17 psi equates to, but its more. That much im certain of. That more actually equates to less fuel mileage!

So we may feel a bit more power from the increased amount of fuel going through the injector but isnt it going to jut hit fuel mileage? Wouldnt we want the least amount of fuel pressure needed for proper performance to maintain highest fuel mileage?

I just ordered the regulated return from RiffRaff. i plan on starting with the lowest fuel pressure spring for a tank and swapping to the highest. It should be pretty easy to see a significant mpg drop.

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My three rules for 7.3l troubleshooting: 1) Replace CPS and keep a spare. 2) Replace FPR and know your fuel pressure. 3) Hook it to a scanner and check for codes.
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post #2 of 9 Old 01-25-2012, 12:09 PM
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No, absolutely not...

The extra pressure would only come into play in the fuel available to the entire system. That is, it could conceivably be an advantage as 6 & 8 fire one after the other, that having a Tiny bit more fuel pressure in the rail could help offset some of the starvation there (if it took place at all...)

On the injector side, you're just filling a cavity (before the HP oil starts to work on it) and, because you can't compress a liquid much, the "CC's" held in that cavity isn't going to change because of a 10% increase in pressure. You're not getting 10% more fuel in there at each cycle.
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post #3 of 9 Old 01-25-2012, 12:51 PM Thread Starter
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ahhh, that is the piece i wasnt aware of. So there is a finite space within the injector that is filled and controlled before being "fired". Thanks for that.

Nonconformist. Functionality over bling.

My three rules for 7.3l troubleshooting: 1) Replace CPS and keep a spare. 2) Replace FPR and know your fuel pressure. 3) Hook it to a scanner and check for codes.
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post #4 of 9 Old 01-25-2012, 07:46 PM
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Higher fuel pressure = More atomization of the fuel spray. Atleast that was what I was told.
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post #5 of 9 Old 01-30-2012, 06:57 AM Thread Starter
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Now that contradicts what Ralph says

Nonconformist. Functionality over bling.

My three rules for 7.3l troubleshooting: 1) Replace CPS and keep a spare. 2) Replace FPR and know your fuel pressure. 3) Hook it to a scanner and check for codes.
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post #6 of 9 Old 01-30-2012, 08:20 AM
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No, no, no, that might be what's happening in a Gas motor, where the fuel pump determines what the injector injects, but Our injection system is driven by the HiPres oil In each injector. So, yes, increasing the Hi-Pres oil pressure might get better atomization but our Fuel Pumps job is merely to deliver sufficient fuel to those injectors so it can be "worked" on by the HPOPs oil.
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post #7 of 9 Old 01-30-2012, 08:23 AM Thread Starter
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Any reason not to go for the highest pressure (70 psi)? I have a dead rail elimination kit that allows me to select from 1 of 3 springs to modify fuel pressure. 70 being the highest. As long as i have no leaks from 70 PSI, continue with it?

Nonconformist. Functionality over bling.

My three rules for 7.3l troubleshooting: 1) Replace CPS and keep a spare. 2) Replace FPR and know your fuel pressure. 3) Hook it to a scanner and check for codes.
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post #8 of 9 Old 01-30-2012, 08:42 AM
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Sure, it won't hurt anything. I'm not positive it's really going to help, not sure if any of us actually needs higher pressure for any reason. But, when I did my FXR I too put the heaviest spring in it
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post #9 of 9 Old 01-30-2012, 08:44 AM Thread Starter
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All i can hope for is higher fuel pressure may help when desired fuel volume becomes very high (high rpms). Thanks

Nonconformist. Functionality over bling.

My three rules for 7.3l troubleshooting: 1) Replace CPS and keep a spare. 2) Replace FPR and know your fuel pressure. 3) Hook it to a scanner and check for codes.
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