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monroe74 · 05-13-2008, 01:14 AM

whoops: "if you can keep it in leaner burn mode and you can keep your rpm down, you are going to get better mileage"

Thanks for jumping in.

Actually, I think I'm finding that I do better if I sacrifice lean burn in order to minimize pumping losses. Although the situation could shift at highway speeds, as metro astutely noticed.

"What I found was that on my car it would stay in closed loop, monitoring the oxygen sensor, until about 80-85% throttle. At that point, it would go into open loop and the oxygen level would decrease substantially."

As you pointed out, a fundamental difference between my car and yours is that I have a wideband sensor. I tend to believe that this means I don't suffer from the same kind of non-linear response that you just described. In other words, WOT doesn't trigger open-loop, or if it does, the ECU is still managing things in a moderate way, so there is no threshold where suddenly an extra penalty kicks in.

I'm more convinced of this as I monitor my injectors. As I move the throttle from 50% to 100%, the injectors respond linearly. In other words, there seems to be no threshold where they suddenly decide I need lots of extra fuel.

The injector duty cycle seems to be a direct function of throttle position and RPM (i.e., vehicle speed and other factors seem irrelevant). In any gear, WOT at very low RPM (say, 1000) yields a quite modest duty cycle of roughly 10%, which is only about 10 times greater than idling. WOT at 2000 rpm means a duty cycle of about 20% (the numbers are conveniently consistent, that way).

I have the idea that idling costs about 0.2 gph. So my rough calculation is that WOT at 1000 rpm is costing me 2 gph. In my overall P&G routine, WOT is only a portion of total elapsed time. Anyway, these rough numbers give me a framework to try to assess how I'm doing.

05-13-2008, 01:14 AM	#39 (permalink)
monroe74 EcoModding Lurker Join Date: May 2008 Location: USA Posts: 59 Thanks: 0 Thanked 0 Times in 0 Posts	whoops: "if you can keep it in leaner burn mode and you can keep your rpm down, you are going to get better mileage" Thanks for jumping in. Actually, I think I'm finding that I do better if I sacrifice lean burn in order to minimize pumping losses. Although the situation could shift at highway speeds, as metro astutely noticed. "What I found was that on my car it would stay in closed loop, monitoring the oxygen sensor, until about 80-85% throttle. At that point, it would go into open loop and the oxygen level would decrease substantially." As you pointed out, a fundamental difference between my car and yours is that I have a wideband sensor. I tend to believe that this means I don't suffer from the same kind of non-linear response that you just described. In other words, WOT doesn't trigger open-loop, or if it does, the ECU is still managing things in a moderate way, so there is no threshold where suddenly an extra penalty kicks in. I'm more convinced of this as I monitor my injectors. As I move the throttle from 50% to 100%, the injectors respond linearly. In other words, there seems to be no threshold where they suddenly decide I need lots of extra fuel. The injector duty cycle seems to be a direct function of throttle position and RPM (i.e., vehicle speed and other factors seem irrelevant). In any gear, WOT at very low RPM (say, 1000) yields a quite modest duty cycle of roughly 10%, which is only about 10 times greater than idling. WOT at 2000 rpm means a duty cycle of about 20% (the numbers are conveniently consistent, that way). I have the idea that idling costs about 0.2 gph. So my rough calculation is that WOT at 1000 rpm is costing me 2 gph. In my overall P&G routine, WOT is only a portion of total elapsed time. Anyway, these rough numbers give me a framework to try to assess how I'm doing.