Exactly what does a typical ECM fuel map look like on one of the closed loop Harley-Davidson systems? Here is a chance to take a closer look at a typical emissions controlled fuel map just as HD provides them to their customers. It will give you a lot of insight into the inner working of Harley, EPA requirements and a better idea why Nightrider XiED's are as effective as they are on these bikes. This will show you the critical portions of the ECM fuel, bias and ignition maps for the 103 Stage 2 download and the Stage 1 download. The Stage 2 is the upgrade that includes the SE-255 cams, so it would be considered a mild performance upgrade. The Stage 1 Download is the upgrade Dealers push so hard for riders to get if they upgrade exhaust and air cleaner. Both these upgrades are valid 50-state legal modification.

For Riders with SERT, SEST or TTS, there is nothing new here. For riders that do not have a software tuner, the information can be quite interesting.

Most riders want to start with the Air Fuel Map, so here it is. Notice all the cells in 'red' with the 14.6 AFR in them. This is the indicator to the ECM to run in closed loop mode, looking at the O2 sensor to determine if the engine is running at the desired fuel mixture. You will notice that the engine stay in closed loop to 3750 RPMs and 80kPa. The HD engine used manifold pressure or engine vacuum from the MAP sensor to determine the actual engine load. There is not a one for one correlation between throttle position and the MAP sensor reading, but this range is basically up to around 40% throttle.

The main thing to notice here is that the majority of riding time, the ECM is in closed loop operating mode. The O2 sensor is controlling the fuel mixture 95%+ of the time for most riders. The AFR table for H-D Stage 2 103 and HD Stage 1 for the 96 CID engines are virtually identical. If Harley-Davidson's Stage 1 and Stage 2 AFR tables are identical, you can make a reasonable assumption that the OEM AFR table is going to be the same or very similar.

The closed loop bias table shown below provides the 'centering' voltage that the ECM will try keep the mixture at when operating in closed loop mode. At a value of 500, the AFR is 14.6:1. As the values approach 700, the AFR actually is closer to 14.3:1. This is at least .3 AFR richer than most riders think the fuel mixture of their bike is actually operating at. For these bikes, H-D is richening the mixture as the load on the bike goes up. But the ECM is actually doing this automatically. So while the engine is idling around 14.6:1, the engine spends much of its time running around 14.5-14.4:1 AFR based on the closed loop bias values placed in the tables. This first map is from the H-D Stage 2 download. Notice how HD very definately richens the mixtue by raising the O2 Bias Values as the RPM and Engine Load goes up. This adds a significant amount of fuel when the bike is moving, but keeps the AFR at 14.6:1 when the engine is idleing.

This second bias table below is from the Stage 1 download. Notice that the bias values are considerably lower, keeping the AFR about 0.1 leaner than the Stage 2 fuel map. H-D is still keeping the bias values considerably higher than the 500 millivolt value of 14.6:1, but they definately are not richening the values as much as in the Stage 2 download.

The Ignition Map is probably the least understood table for the engine. There is a series of cell in the map that form a sweet spot that the engine is under load. The ignition map 'under load' follows a different set of rules than when the engine decelerating. It is fairly obvious from the table below were the engine is really under load and where you are 'off throttle'. There are also a lot of concessions to emissions regulations in this ignition map. But as far as a general purpose ignition map that could be used in most street bikes, this map could be used in a wide variety of situations.

The HD Stage 1 Ignition Map is listed below. It is very obvious that this map is more aggressive, with more advance. The exception is in the higher RPM, off throttle situations. The reason for this is generally to help reduce decel popping.

I hope this brief look at some portions of the ECM tables, namely the AFR map, the bias tables and the Ignition Advance map for the Harley-Davidson Stage 1 and Stage 2 bikes will provide some inside into how your own bikes ECM is set up. I am not trying to explain EFI and Dyno tuning here, just show what H-D did or has not done with their downloads.

The specific SERT Maps used to show this information was 200UH001-A1.MT6 (SE Stage 2 103 + SE-255 Cam) and 200TD001-A1.MT6 (SE Stage 1 TC96).