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Old 08-29-2012, 05:00 AM   #11
roger 04 rt OP
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Joined: Nov 2011
Location: Massachusetts
Oddometer: 2,150
Someone asked me the other day to take a test ride with fuel pressure set to 52 psi, Motronic reset and in Open Loop mode (Wideband O2 sensor unplugged). I got out yesterday and made the run.

My report is simple, the bike runs great--smooth, good power, very responsive to throttle from 2000 RPM or so on up, even in 4th gear. A lot like the Closed Loop test rides at 52 psi and Wideband O2 set to 13.8:1. It's not really a surprise to me that it ran well in Open Loop. But I want to point out one thing: because I had the Wideband O2 installed, I knew that my setting of the fuel pressure was producing the enrichment I was looking for. Without the Wideband O2, you can crank up the fuel pressure, but you can't say for sure where you are with the enrichment.

If you go back earlier in this thread to here: Open vs Closed Loop, notice how much flatter the Closed Loop curve looks and how much tighter the histogram distribution of AFRs is in the smaller plots.

The same thing happened yesterday when I rode at 52 psi, reset Motronic, Open Loop. The range of AFRs, rather than being tightly centered on 13.8:1 where mostly around 14.3:1 and 13.3:1 (the two horizontal dashed lines in the plot below). My educated guess is that this is how the Motronic tries keep the Catalytic converter running even if the O2 sensor is dead. Normally in Closed Loop, with a stock sensor, the Motronic runs fueling a few percent above and below 14.7:1. (Snooze alert: The reason for going to the lean side of 14.7 is to allow Oxygen to recharge the Cerium in the three way converter.) So now, Open Loop the Motronic makes big moves in the fueling, still hoping to create a lean-of-14.7/rich-of-14.7 scenario. This way too rich/way to lean is a sort of limp-home-mode. (It's noteworthy that this will be how many PowerCommander and Techlusion curves would look if anyone plotted them.) I think it is very likely that this causes more fuel consumption than the Closed Loop case.

So here is the Open Loop 52 psi plot with all its "wildness".




My favorite configuration remains:
LC-1 set to 13.8:1 with Fuel Pressure boosted to 52 psi (for E10 fuel).
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