Managing EGR for MPG

[DRW]

Thanks to the inspiration I get from this site, I dug into the ECU disassembly for my car and found an interesting section. The problem is, I'm not sure what to do with it? Here's a copy/paste, have a look:

;************************************************* *******
;
; EGR solenoid duty cycle
; as a function of rpm(column) and airVolume(row)
;Value of $00 to $80 will produce 0 to 100% duty cycle
;************************************************* *******
t_egrDutyFact
#ifdef E931
RPM 500 1000 1500 2000 2500 3000 3500 4000
Load
1. $10 .byte $00, $00, $00, $00, $00, $00, $00, $00
2. $20 .byte $00, $00, $00, $5b, $56, $4c, $4d, $00
3. $30 .byte $00, $00, $00, $5b, $56, $4c, $4d, $00
4. $40 .byte $00, $00, $00, $5b, $56, $60, $5c, $00
5. $50 .byte $00, $00, $60, $76, $6c, $5f, $5b, $00
6. $60 .byte $80, $80, $80, $7d, $6e, $5f, $60, $00
7. $70 .byte $80, $80, $80, $80, $76, $68, $61, $00
8. $80 .byte $80, $80, $80, $80, $80, $60, $61, $00
9. $90 .byte $00, $80, $80, $80, $80, $78, $6e, $00



;************************************************* ********
;
; EGR solenoid duty cycle as a function of ECT
;
; Value of $00 to $80 will produce
; 0 to 100% duty cycle
;
;
;************************************************* ********
t_egrDuty .byte $80, $80, $5b, $4f, $00, $00, $00, $00

ECT degreesF- 186 176 125 95 69 46 19 3 ->
************************************************** ********

As you can see, this is where EGR is handled. I know where this section is located in the code, so I can change any of the bytes to adjust the duty cycle.

I've searched for good articles about EGR, but mostly I seem to find basic info about what it does. As you might have guessed from the disassembly, I'm looking for reasons why EGR might be useful or harmful to FE when increased/decreased as the engine sees different loads and different temperatures. If needed I can also make adjustments to the fuel and/or ignition timing maps to optimize the EGR effect. But like I said, where do I start? If anyone out there has run across some detailed tech info about EGR, let me know. I'll keep searching too. If the code isn't clear, just ask.
Thanks!

Dave W.

[rh77]

This is all just a guess...

Since ECT regulates the EGR as a function of emissions/warmup, that part should probably be left alone.

I'd reccommend "baby-steps" in introducing small amounts of EGR in low-RPM, low-load situations and see how driveability and FE react.

For example, in the $40 column of load, at 2000 RPM, add a $4f (from the engine temp byte); see how that works, and do the same for $30 and $20. Since it's an experiment, document your findings at each change, and see what happens.

I would then keep adding a small amount of EGR at lower load and RPM, if it works, and maybe until it's no longer running properly or efficiently.

I couldn't tell from the data, but is there a smaller amount than $4f for EGR duty (such as $3x)? You may look into that and add even smaller amounts if the larger one is too much. Good luck!

RH77

[cfg83]

DRW -

No intelligent statements, but here is what the data looks like in 3D :



CarloSW2