Compression Ignition Addict
Join Date: Jul 2010
Location: Falls Chruch
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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.
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.