How much is to much fuel pressure for hwy driving/mileage?

[Dozerboy]

I don't know how long it's been but my mileage has been in the crapper on my LBZ. 15 years ago when I would daily drive my truck with my tuning I could get 19mpg at 65mph and 17mpg at 75-80mph. Now days I might get 16mph at 65mph, 15mpg at 75mph, and 14 at 80mph. Not sure what's all the cause from the modified VVT, head gaskets, 100overs, or a 12mm stroker. I don't really care, because it's only a weekend truck. I'm usually out to enjoy myself when I'm driving it, but it irritates me on long trips a little bit. I feel like when I did head gaskets/injectors I lost the most MPG. That was in 2020 and the injectors where from LDS. For sure since I did 100overs my truck runs dirtier at hwy speeds, so my thoughts are I'm getting poor combustion and maybe more fuel pressure would help.

While cruising I'm currently running as much timing as I can I feel like can at 12-12.5*. My fuel pressure at 65mph is 102MPa with a 650us pluse width. At 80mph its 124MPa with a 605us.

I feel like I've read before that it's hard on injectors/CP3 to be running too much fuel pressure. I'd love to try and squeeze some more mileage out of it, but not at the cost of wearing out my fuel system. Before I went back and looked at where I got injectors from I called Exergy about it and they said as long as I'm not over 200KPa it was fine for the injectors. I forgot to ask if thay was the case for the 12mm too.

Thoughts?

 

[2004LB7]

12+ degrees seems like too much for 100 overs, we run around that woth stick aticks. . I would guess closer to 8° would be closer to optimal for 100's. But you are running only around 14k psi. May try bumping up to 125 mpa and drop timing a few degrees to see if it helps. Too much timing and your fighting the upwards travel of the piston

 

[PureHybrid]

Too much pressure can hurt mpg as well, fuel makes it too far into the bowl before ignition begins under low cylinder pressure / temp. I'm with Jason though, I'd try to drop timing low and start working back up again

 

[Ridin'GMC]

You guys need to take consideration that timing plays a role with fuel pressure. Too much timing and too much fuel pressure will most definitely hurt fuel mileage and cause a pinging sound. Best way is lower fuel pressure with moderate timing, i.e. 10-12k psi in the cruising range with at least 8-11⁰ of timing seems to work. On my lbz with stock injectors, stock fuel pressure or slightly lower with about 8-9 degrees of timing is where I got the best fuel mileage. Right now my mileage is shit with worn out injectors and it dropped 2 mpg when I deleted the air intake heater and went compound. Deleting air intake heater does cause more fuel consumption during warm up which causes to lose fuel mileage initially, Idaho Rob said this part about the intake heater.

 

[Chevy1925]

Large injectors are fun to tune mpg back in

P to h clearance plays a roll too

Me tightening up p to h from
.035 to .025 got me 1mpg gain even with going from standard bowl to fingers.

I still have more to play with on my tune but pilot injection and pilot timing makes a difference for mpg too. I cant remember which way i went but i think i decreased injection amount slightly and timing.

You have to realize that adjusting rail then affects all pre/post injection and how optimized timing is. That then plays apart for every other table you change. You cant just change one and expect it to not affect the other. Could go positive or negative. My struggle has always been “which do i mess with first and how does it affect the next table”

 

[slidinDuramax]

I have a set of bd 43% injectors and got close the first time around was getting around 21mpg with 9 deg and right around 11kpsi still datalogging and making changes as I drive it more. Is there anyway make the transmission survive better running a dsp switch or how long does it take to adapt to tune change. The trans is stock and I know I'm on borrowed time.

 

[Dozerboy]

Large injectors are fun to tune mpg back in

P to h clearance plays a roll too

Me tightening up p to h from
.035 to .025 got me 1mpg gain even with going from standard bowl to fingers.

I still have more to play with on my tune but pilot injection and pilot timing makes a difference for mpg too. I cant remember which way i went but i think i decreased injection amount slightly and timing.

You have to realize that adjusting rail then affects all pre/post injection and how optimized timing is. That then plays apart for every other table you change. You cant just change one and expect it to not affect the other. Could go positive or negative. My struggle has always been “which do i mess with first and how does it affect the next table”

I remembered you talking about that and kept that in mind when I did my HGs. I don't remember what I was at for sure. I think used Bs and had 0.030 on one side and more on the other because I didn't want to buy 2 sets of HGs.