How to read logs (rail pressure) now with PI injection


Apr 18, 2020
bmw 335is DCT
Gforce boost controller
Doc race 6266
Stage 3 LPFP e85
PI /AIC controller

Hello everyone, I am installing PI soon and this is new to me and I am trying to understand how this works and how I can read logs to make sure I am getting properly fueling like I normally do.

so I understand Rail pressure HPFP should be above 1500 and LPFP should be above 50 consider values for healthy fueling.

so now with PI in my understanding that doesn’t effect the Railpressure so would rail pressure keep decreasing as I turn up my boost as the dme thinks it needs more fuel as PI is spraying??

Rail pressure won’t increase with PI so how do I know if I am getting enough fuel or so I only monitor AFRs now?
how does rail pressure get affected when running 25+ psi I don’t understand how I can read logs now and know my fueling is healthy as there is no way to monitor PI spraying?


Jan 9, 2018
Just North of Detroit
BMW 335is
Your post is a bit confusing but I will give it a shot.

I think you are asking, how does the DME know how much fuel to spray?
The port injection will have a controller like the AIC-6, which has fuel tables and communicates with the DME. Your tuner can adjust the tables depending on requirements.

FYI, I have a port injection rail with injectors and controller I might be selling, if you are interested, PM me.


Platinum Vendor
Jan 23, 2017
Your questions are part of the reason the JB4 with integrated PI controller is so vastly superior to your two separate stand alone piggybacks. :)

The JB4 lets you map out PI flow on various engine criteria including the very important low fuel pressure (which when combined with boost impacts effective injection pressure), monitors injector flow so you know it's working, auto adjusts PI volume based on various criteria, monitors fuel trims in both banks to flag an imbalance on the fly before something melts down, biases fuel trims under PI flow to keep them level, etc, etc.

The basic formula though for PI tuning is:

Set PI volume to the lowest level such that fuel pressure is maintaining at target, zero out fuel trims so they are more or less level at all boost targets run.
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