linksys42
20+ Year Contributor
- 412
- 30
- Jan 8, 2003
-
Union,
Missouri
Taboo said:Reset the ECU to start with (in order to get rid of your messed-up trims and load fresh timing maps), reset the ISC servo, pressure-test the intake, make sure the TB plate is all the way closed at idle and all the way open at WOT, adjust the TPS, and set the BISS 2.5 turns out. Set the S-AFC to 0 or slightly bellow across the entire board and use NOTHING but the AFPR to get within the ECU adjustment range (= do not touch the S-AFC AT ALL. Just pretend it's not even there). The trims do NOT have to be exactly 0%. Adjust the idle with the BISS. All there's to it. Use just and only the AFPR to establish the rough fuel curve and the S-AFC to supply the ECU with the correct airflow. Because of the hacked MAS (or different turbo response - in case of someone with an aftermarket turbo) the "correct" airflow the ECU expects to see is not going to form a straight line on the S-AFC and does not really mater where the curve on the S-AFC is located as long as the ECU is supplied with the "correct" airflow values. One can and will use the S-AFC to fine tune the fuel curve (once it's established with the AFPR), but there's going to be never ending compromise between manipulating the actual AFR and affecting the timing in the process by feeding the ECU by "incorrect" airflow values. There are just two simple things you have to do: 1) establish the correct airflow values with the S-AFC and 2) establish the fuel curve with the A-FPR while staying within the adjustment range of the ECU. If you do that, your car is roughly tuned and you can continue fine-tuning it with the AFPR and the S-AFC in order to improve the throttle response, get rid of knock caused by incorrect AFR or timing at particular RPM range and airflow, etc. Don't be obssessed with 0% trims and 0 knock. Lean the bi*** out (with the AFPR) as much as you can at WOT 'til she starts dropping timing, then go a notch back up with the fuel pressure. However, you can do that only after the LTFT is established.
I was wondering if this approach to tuning would be fine with 650s? Because to get the O2s to cycle I would think you would be pretty low in the fuel pressure with the AFC zeroed out with the 650s. What I am wondering is how low of fuel pressure is to low? At what pressure will injectors still atomize fuel well? Because at 30 psi of base fuel pressure you should be able to flow the 650s at about 448cc. And at 37psi of base pressure I should be able to run the injectors at 552cc. Correct me if Im wrong. Just wondering how low of fuel pressure is safe when tuning with an AFPR. Thanks

I only have a shallow knowledge of how these things interact...I don't want to tell you the wrong thing!
so I settle for 4 "counts" of knock. Technically though, no knock is safe, since any knock has a really violent effect on what goes on within your cylinders.