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Fuel Pressure not as desired - 2014 6.7 Cummins

Practical Diesel Tuning

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I am currently working on a 2014 6.7 Cummins with a 10mm CP3, 30% over Injectors, Fleece 63mm Turbo, Banks Air Horn, Upgraded Intercooler and an Injen intake. A FASS lift pump is also installed. For test purposes I replaced the FPRV with a Plug.

My problem is that the truck doesn’t go over 170 MPA Fuel Pressure once is demanding it and even drops slightly under 170. This is at the pulsewidth provided by the flow sheet from the manufacturer of the injectors. If I run higher pulsewidth I can’t even go over 170 MPA when commanded is 180-190 MPA. How does the fuel pressure react to longer injector on time? Should it still hold it’s commanded 180 MPA and even more since this is a pretty solid pump? Truck is obviously smoking crazy before the turbo spools since injection duration is longer with less fuel pressure. Maybe i am lacking some knowledge here. Could that also be not the real fuel pressure in the rail? Also i havent touched the fuel pressure regulator map yet, maybe it needs some tweaking at the bottom? I have attached a log file with the higher tune and longer pulsewidth.

Injectors run 207mm3 @ 1800 Bar or 180 MPA at 1700 us.



For some reason your fuel system is unable to keep up at the ~2900us Pulsewidth command. There are a variety of reasons this could happen ranging from inadequate low side pressure, to regulator tuning, to return fuel rates. Short answer is that you'll want to either solve for the pressure differential or back off pulsewidth off until the system can keep up. Try targeting 2500us instead and see what happens.

For the info supplied, the 10mm pump should be able to deliver full pressure if all of the mechanicals are solid.

Hopefully this is useful info,


Thanks nick, i think the opening time was just to much for the injectors. They should deliver the 30% over at 1700 us opening time and it was way above what was commanded. Truck runs fine now. I have now another issue with my CSP5 Tune. Each Slot has different Pedal to Torque commanded but each tune commands the same Torque (1900 NM). Why would that be the case? Also even though 1900 is commanded i cant get full fuelling, though all limiters are already up.

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