roger 04 rt
New member
I have avoided working with Alpha-N, seems to ignore so much of what is taking place on an engine. With "Speed Density" actual conditions are being utilized plus for a turbo'ed condition it is much superior, as loading and boost can be all over the map so to speak, even with a throttle setting that is constant. Some squirters have adopted the blended "Alpha-N/ S.D." tables which can help with engines having poor "map" characteristics but are boosted. Our boxer engines having two cylinders might qualify for that concern but I have found stability even at ultra low idle states such that I have no concerns.
Each item you provide here seems to help paint a picture of what the Motronic is striving to do, and how under certain conditions the unwanted oscillation might take place.
Really appreciate your informative approach.
Lorne
From what I've read, using speed-densitiy (manifold absolute pressure) on a single cylinder engine (we have two on the same crank from a fueling perspective) doesn't result in a reliable signal from the MAP whose signal can bounce all over the place at low RPMs. Are you saying that's not the case from your experience?
--At low RPMs and small throttle angles a 3% change in throttle angle requires a 34% change in the amount of fuel injected to maintain a constant AFR. That means that a small TPS sensor error, or small change in air flow through the throttle body could result in a significant mixture error, leading to the conclusion that precise Mixture Adaptation is a necessity for accurate fueling at light loads.
RB
Hello Roger,
I think the above quote from your last post pretty well sums up the reason why many of these oilheads exhibit the annoying tendency to surge at slow speeds and why the narrow band O2 sensor with its characteristic slow response time does not much to alleviate the problem. This also leads me to think that the LC-1 controller with the fast response wideband O2 sensor is the best option for use with these machines.
Hi Jim, I hear you and see your point. Bosch says the Motronic concentrates a large number of the LCF cells and Fuel Map in the lower RPM, lower TPS area--as usual we don't know exactly what that means but the chart is giving their rationale for that decision.
Even though the stock O2 sensor is slow, and it takes a bit of time to compute the LCFs initially, once computed they are available to the fueling calculation without any delay, same it true of the Mixture Adaptations.
WallyG and I each have a small amount of LC-1 data taken at light throttle during a "surge" event. It is not at all conclusive that the Motronic is modulating the fuel causing surging. The data is not conclusive that it's AFR variation causing surging. The best way for me to test that is to program the AFR on my bike to 16:1 to 17:1 and see whether I get consistent surging, and then see what the LC-1 reports. It's hard to get surging when you want to measure it.