Ok guys...

I got the gauges here now they have been working flawless for about 2 months now.

But I want to verify my idea with you all...

My fuel presures are..

15.5-16.0 PSI Starter Bump (no change)
14.5-15.0 PSI Idling (no change)
10.0-12.5 PSI Cruising (65 MPH) - Used to be 12.5 -13.5 PSI
8.0 - 9.0 PSI WOT (no change here)

According to my maintenance logs I've still got 5K to go for the fuel filter to be replaced... But I'm starting to wonder if the gauge is show the filter plugging up. What do you guys think just change it to see? Or what next...??

Also the FP gauge is POST filter setup... I've got a isolator needle valve!

 

Hmm....that is a tough call......it is strange that your FP is only different at cruise. Are you able to measure pre filter FP? I have a gauge mounted on the filter head that measures pre filter and the gauge in the cab measures post filter. I would lean more towards the LP as the problem because it is inconsistent......I would think a plugged filter would cause a pressure drop across the board. I guess the easy thing to do would be to change the filter and see if the problem goes away.....if it doesn't, then I would suspect the LP as the problem.

 

Strange huh... Nope... no pre filter setup (Mechincal gauge - DiPricol)

I'm starting to lean on the filter being dirty... But the LP was replaced no long ago about 3K miles. The starter bump PSI is still nice and high. I'll do a volme check of the LP...

So my theory is that being the guage is POST filter and the filter is start to become a restriction to flow. The pump is consuming a fairly steady amount of fuel (cruise mode) and less is being returned (PSI Drop). As I decelerate to a slower speeds the FP comes back up to 12.5-13.0 PSI the slower I get. (Less consumtion) But as the RPM's go up and the skinny pedal go down FP will drop down... (More consumtion) But the VP can only consume so much fuel (stock configuration) at WOT which I assume is the 8.0-9.0 PSI

I'm kinda of look at the FP guage like a flow meter in a way...

High Pressures - Low Flow of Fuel
Low Pressure - High Flow of Fuel

My FP has never drop below 7.5 PSI yet.

I'm going to find me a fuel filter then...