Tuneboy fuel and A/F tables

The "look-up"base tables are just that. The narrow band stock O2 sensor only works at low rpm and low throttle settings (possibly in cruise conditions, but I haven't been able to confirm it yet), becaust the sampling rate cannot keep up with acceleration rate of the engine. As a result, the ECU checks rpm and throttle setting and "looks up" the amount of fuel and spark timing to use for this RPM/throttle setting.

Getting the table correct is termed mapping. Mapping can be done for best power, emmisions, economy, or a mixture of all of the above.

The A/F table is an alteration from the basic tables. This allows the base tables to be corrected for changes in altitude and atmospheric conditions. A wideband sensor would be better than the stock one, but would still need accurate basic tables under hard acceleration.

The A/F table really is only used when A/F values in the map are above 14.5 - I believe. I am still trying to get a good grip on how the Keihin and Sagem ECUs work and differ.

But, I hope this helps.

I believe that the stock O2 sensor works over a broader range than many give it credit for using. Either way, mapping the base tables accurately will always work best. The less alterations the ECU makes to these tables, the better.

Either way, even with a wide band O2 - or even a good true Lambda - sensor, the readings follow the actual power curve by several hunded rpm. In drag racing, the wideband is used for quick mapping, and then the tables are corrected to best power and response based on actual load. A Dynojet does NOT load the bike (or anything else) the same as in real life. More load requires more fuel for best power.

An engine that is correctly loaded and mapped, will out perform one that is simply mapped to an AFR based on a dynojet. THIS I know to be fact, but take it as you will.

My Tuneboy has the PC map I got from Zard with the exhaust. It ran well with the PC and it runs well on the Tuneboy. I've bumped up the ignition trim a little and the bike really runs well. If I was smart I wouldn't mess it but.......... Here's what the Tuneboy documentation says about the A/F:

'The A/F table is used to calculate the ratio of fuel to be added to the air in the cylinder. This has nothing to do with oxygen sensors in the exhaust and applies even if your motor does not have a sensor. The way the A/F 1 table works is simple. If the ECU calculates from the fuel table that the motor has 300 milligrams of air and the target A/F ratio is 13/1, then the ECU needs to add 23 milligrams of fuel...............'

This function sounds identical to the fuel map. Like it determines the amount of air going into the cylinder at each stroke then uses the lookup table for the amount of fuel required. No feedback from the O2 sensor. What would this do if the amount of fuel based on the above was not the same as the amount specified in the fuel map?

I've read the Tuneboy literature, and I still don't fully understand the ECU and the effect the A/F tables have over the standard look-up tables. The Tuneboy documentation is good, but not detailed enough to answer all my questions.

I am no newcomer to EFI, and have used many different software packages and aftermarket engine management systems over the years. I have had a very good working relationship with JGM (Motec USA) and Motec AUS - I've been their guinie pig for several products from the CDI8 to the GPS units. But I cannot get a clear picture in my head of exactly how the Keihin ECU manages fuel. I'm sure it is simple, but info from Tuneboy and from Keihin are not clear enough.

I guess it is time to fire off another detailed list of questions to Wayne Macdonald at Tuneboy. He HAS to be getting tired of my harassment by now.