Having Issues Getting Fuel Rail pressure to stabilize

[guimond47]

Ive been tuning my truck for a few weeks now and ive been really happy with the performance of where ive gotten it. the one concern i am having is trying to stop the Fuel Rail pressure from fluctuating in the logs. It doesnt seem to be effecting performace but it might be. i wont know until i can get it to flat line in the logs.

Its fluctuating about 400 bar up and down.

the truck is a 2010 6.7 cummins with 135% overs, 12mm Pump, and modded fuel rail.

i had tuning from someone else and their tuning was smokier then mine but fuel pressure is not fluctuating. There for there must be a solution to this.

Here are snap shots

fluctuation of FRP.PNG

[abgreenmachine]

Pressure relief valve on the fuel rail would be my first guess
Put a plug in for testing only and go from there

[guimond47]

That would be an option but i dont have a plug. it is also not a mechanical PRV. its electronic. It may cause issues doing so.

[bluessmax]

Ive been tuning my truck for a few weeks now and ive been really happy with the performance of where ive gotten it. the one concern i am having is trying to stop the Fuel Rail pressure from fluctuating in the logs. It doesnt seem to be effecting performace but it might be. i wont know until i can get it to flat line in the logs.

Its fluctuating about 400 bar up and down.

the truck is a 2010 6.7 cummins with 135% overs, 12mm Pump, and modded fuel rail.

i had tuning from someone else and their tuning was smokier then mine but fuel pressure is not fluctuating. There for there must be a solution to this.

Here are snap shots

fluctuation of FRP.PNG

What is happening is the stock curve for the regulator is too aggressive for a larger pump. It is great at metering a stock pump, however, on a larger pump that curve needs some love. Datalog the mA from the regulator during the surge condition and then in that area.. start by increasing it by 10%. Normally, it will only be about the last 4 cells of the curve you need to mess with. Keep it linearized with a few cells above where you made the changes and you will be able to clean it up quickly. I also recommend for running higher pressure to increase the very top cell of that curve by around 250mA to give the reg some headroom during abrupt "Off throttle" conditions so it can bypass excessive pressure and not hurt the injector.

Good luck!
Kory

[NRunkle]

What is happening is the stock curve for the regulator is too aggressive for a larger pump. It is great at metering a stock pump, however, on a larger pump that curve needs some love. Datalog the mA from the regulator during the surge condition and then in that area.. start by increasing it by 10%. Normally, it will only be about the last 4 cells of the curve you need to mess with. Keep it linearized with a few cells above where you made the changes and you will be able to clean it up quickly. I also recommend for running higher pressure to increase the very top cell of that curve by around 250mA to give the reg some headroom during abrupt "Off throttle" conditions so it can bypass excessive pressure and not hurt the injector.

Good luck!
Kory

When/would you adjust the duty cycle on the pump? or is that more for when you are starting to run out of rail and need to increase it?

[bluessmax]

When/would you adjust the duty cycle on the pump? or is that more for when you are starting to run out of rail and need to increase it?

I always try to think of how to simplify things down from a physical standpoint. If I have a pump producing TOO MUCH fuel and that is what is causing it to surge... then I need to limit the fuel to the pump. The only way we can limit fuel to the pump without sacrificing overall volume is by squeezing on the regulator harder to limit the amount of fuel being put into the fuel pump. By increasing the mA to the regulator - we are essentially lowering the amount of fuel entering the pump. Once we get the amount of fuel entering the pump under control by increasing the mA to the regulator - we will then no longer have a overpressure condition.

Just like a garden hose that was shooting too far... You gotta limit the flow. So we do this with the regulator by increasing the mA (Higher numbers) so that way it can meter the fuel in at the appropriate time!