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Differential Fuel Pressure

Howard Coleman

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i have 2 issues. one is my issue ( i am losing static pressure under boost. from 41.2 at static to 39.2 at 18 psi.)

the other issue is why i write:

my Differential fuel pressure appears to be going the opposite (rising) direction. if the pump, regulator, lines and filter are O K DFP should remain constant. rising DFP under boost points to, often, a restriction in the return line.

yet if i just do the math using my boost and fuel pressure i appear to be losing pressure under boost.



using AN Volt 4 w Honeywell pressure sensor for fuel pressure

i attach a log.// no log, too large... can send a smaller one if necessary

at 4:06.667

MGP Psi + 2 tenths of one psi

AN V 4 fuel pressure reads 41.4 psi

static is 41.2

Fuel Pressure KPA  420


Differential Fuel Pressure reads 410 (doesn't quite match up but that is what it says.... close anyway)


at 4:18.134

MGP PSI 18.2

AN V 4 fuel pressure reads 57.4 psi

static is 39.2

Fuel Pressure KPA is 574

MGP 125

Diff Fuel Pressure 445


DFP  moved from 420 to 445?  while calculated using AN V 4 and my map sensor DFP dropped

any ideas welcomed.


thanks and still love my V88!



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I think I will need to see a log and map (share them using google drive/onedrive/dropbox etc) to confirm but from your detail above I suspect your problem is the mix of units.  The fuel pressure sensor will need to be calibrated in Kpa units for the ECU to be able to calculate diff fuel pressure correctly.  There was no internal unit conversion in the V series so any parameters that are used in ECU calculations need to be in native (metric) units.

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had this issue on a v44, it was the fuel pressure sensor's CAL table being in psi instead of KPA as Adam stated above.  Switched the CAL to KPA and all was fixed.  In the troubleshooting process we did find a poor power feed to the fuel pump though :)

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sure... thanks  Adam and JMP. 

i have five pressure sensors working... fuel, oil, Auxiliary Injection system pressure, exhaust backpressure and boost. since backpressure compares against boost and the majority of people i share my info with think

in PSI i will just calculate Diff F P manually.

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