Fuel rail pressure relief or botched setting?

[computerjlt]

First off i'm pretty new to tuning diesels but not so much to tuning. I've been tuning gas cars for about 10 years now but since I have a dyno and a shop i'm branching out lol.

Anyway I'm working on a 07 6.7 cummins and I got it to around 350/720 tq (not near the dyno pc to look at the exact numbers) but it seems when i try to up rail pressure any more it falls out. I'm taking my sweet ass time making baby changes and logging everything.

Rail pressure will hold 180Mpa no problem it seems but you ask for 190 then it drops to about 82-85mpa. When it does this FCADCA creeps to 90% (i'm assuming the pid loop is doing its thing) but no response from rail pressure.

My question is, is this the popoff doing its duty or did i forget to set something somewhere? i tried playing with the base duty table but it did the same thing

also whats a "safe" or nominal figure to run rail pressure at at WOT? This guy doesn't do any towing, couldn't care less about fuel milleage and just wants to max out the stock turbo. It has no aftermarket lift pump on it at the moment so i'm not ruling that out as a cause but since the truck runs great at 180mpa rail pressure i dont think its the lift pump (yet). He is getting a real EGT gauge, lift pump and probably head studs/gaskets before his next dyno session.

here is a screen shot of the log showing what i'm talking about. if anyone wants the cal/log i can email it to you

lastly if anyone in south texas (victoria) wants or needs some dyno time hit me up, i'd gladly trade dyno time for some more diesel tuning insight or hands on experience.

[2007 5.9]

3200uS@27,000psi is far too much for a stock fuel system.

Most 100hp tunes are in the 160MPa@2400uS

[computerjlt]

I think duration shot up since pressure plummited

The fuel pulse before when rail pressure held was around 2250us at peak torque

[2007 5.9]

Right....as FPA drops, pulse goes up.

You need to adjust the tune to keep FPD/FPA within 10% to keep the rail happy.

Also I can almost guarantee that the egts are sky high with 3200uS@3* of main timing....

[2007 5.9]

And if I'm looking correctly, your commanding over 1000uS at 1200rpm...the pulse graph isint scaled to see the actual pulse at xxxxRpm.

[computerjlt]

Right....as FPA drops, pulse goes up.

You need to adjust the tune to keep FPD/FPA within 10% to keep the rail happy.

Also I can almost guarantee that the egts are sky high with 3200uS@3* of main timing....

i have no doubt, this is NOT how the truck is right now, this was on the first pull where rail pressure dropped. 3.2ms is way too long of a pulse as far as i know.

i reverted back and truck now keeps a happy 2.2ms of duration at 165ish mpa (did a run on the dyno to make sure rail pressrue held).

[anarchydiesel]

If you have the factory pressure relief valve you will blow it open at anything over 26,000 psi rail. You are commanding 27,500 and blowing the valve. shim it or put a race plug in it and the rail will hold.

[computerjlt]

If you have the factory pressure relief valve you will blow it open at anything over 26,000 psi rail. You are commanding 27,500 and blowing the valve. shim it or put a race plug in it and the rail will hold.

awesome thank you, thats what i was figuring. What rail pressure shuold i shoot for or stay under once he gets a lift pump (still on stock high pressure pump and injectors)


and "2007 5.9" the rpm in the log on the screen shot there never drops below about 1600, i can mail you the calibration and log file if you'd like

[anarchydiesel]

If you are just starting out, I would stick with stock max pressure of 26,110psi. Then you can start working your way up to whatever you want. Remember that while pressure makes power it also can be hard on components.