Gen3+ fuel pump control tuning

[engineermike]

I've been digging deep in the fuel pump control logic lately and wanted to share what I've learned.

The "lift" pump control actually works similar to lambda control, in that there is a feed-forward voltage as a function of desired pressure and flow (similar to MAF or injector constant tuning), a fast-acting PID feedback loop (similar to STFT), and a long-term "KAM" learning component (similar to LTFT). Similar to fuel trims, you want your feed-forward to be as accurate as possible so the PID feedback loop and KAM learning are minimized.

ECM numbers are HPT tables, and auF numbers are PCMTec tables.

• The feed forward table is auF30958 or ECM43002.
• The P, I, and D gains are auF41737, 41735, 32777 and 23005, 23002, and 23001, respectively. The P term is the fast acting one while the I gain is slower and more stable. D is not generally used or significant.
• The KAM learning component can be turned off using auF41729 or ECM45694.

My Roush truck has a stock pump but I had added an 18v constant BAP and decided to correct the feed-forward table to account for the BAP. To tune the feed forward table, you have to allow it to have error so you can correct it. This means setting the P, I, and D gains to 0 and turning off the adaptive voltage. As such, the following shows the stock table, and the final table after accounting for the 18v BAP:

Stock:

BAP:

Note that the 6 lb/min column isn't the result of this process. I wasn't able to hit the top right of the table, and the bottom right I wanted max voltage since that is the WOT region. Also of note is that I started out making .5 volt changes and they were really too big. .25 volt increments worked better and would change the fuel pressure by about 3 psi.

Also, it's a good idea to raise the max voltage using auF61353 or ECM43003. Otherwise, it will cap the voltage to the pump even with a BAP. Furthermore, I lowered the min voltage (auF28073) to 3 volts and min duty cycle (auF32736 or ECM6961) to allow it to control at idle without hitting the min limits.

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[mejohn50]

A while back you posted some changes for tuning a fuel pump booster on another forum. Your changes included altering the slope (ECM 6980) and offset (ECM6981) to account for the fuel pump booster.

Does doing what you described in this post remove the need to make the slope and offset adjustments?

 

[engineermike]

@mejohn50 youre correct. Some time back I noticed that my idle fuel pressure was high with a bap and figured out how to manipulate the “slope and offset” constants to get idle pressure into the span of control. I’ve since learned more about how the control works and gained access to more parameters. The issue was that a min voltage or min duty cycle clip was preventing low enough output when the extra 50% voltage was added by the bap, so changing slope and offset was a workaround. I’m now running stock slope and offset and lower the min voltage and duty cycle instead. By the way, slope and offset are used to convert 0-100% duty cycle to 0-50% output to the fpdm.

 

[Pistol_91]

This is how mine is set up. Runs like a champ. The max injector PW i see is between 4-5 with e85.

The DW400/BAP combo would satisfy 90% of people I'd say that want to run e85.

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