There was a recent thread where fuel injection and specifically the function of O2 sensors was discussed. Rather than continue a useless argument in that thread, I decided to provide a little tutorial. A little tutorial from the MoCo.
In a nutshell, there are two types of fuel injection used on Harley's. Way back when, it was a Magneti-Marelli Alph-N system. And they had a lot of issues. Poor parts quality, limited processing power and most of all, poor tech training. This system was used to try to satisfy the EPA's demands for cleaner running motorcycles. And it did, within its abilities, and when it was in proper working order and properly adjusted.
A while later the EPA demanded that the scooters run even cleaner, so much cleaner as to include catalytic converters. The MoCo knew that the MM system was not up to that task, so they adopted a Delphi built Speed Density system.
Here is a power point presentation on the Harley fuel injection system and the tuners that were used to tune it. It predates the epa clampdown, so it includes a little info on the ways to tamper with the oem system
Electronic Fuel Injection for Harley
OK so here are some points from the presentation.
But first, I've added a couple of fuel table representations. Take note of the number in the individual cells. That's what is important.
The system uses pre installed fuel maps to determine how much fuel to provide under any given condition. Many of us have seen visualizations of these. There are many ways of presenting them to the human eye. What's important is the numbers in the cells. 14.6 is the target for closed loop fuel trim. 14.6 is the ratio of air to fuel. 14.6 grams of air per gram of fuel. A lower number calls for a richer mix (more fuel), and a higher number is a leaner mix (less fuel)
Notice how the table avoids 14.6, more on that later.
The MoCo has no choice but to attempt to target the fuel mix at 14.7 to 1. Its the law.
To do this, harley build the fuel tables and then uses a narrow band O2 sensor (Oxygen Sensor) to maintain the fuel trim. This is called closed loop operation. This is only available during idle and light load cruise conditions. The rest of the time the ecm just uses the apropreate setting from the fuel tables. This is called Open Loop. In open loop the O2 sensor has no function. And this is because of the limitations of narrow band sensors. They can only function at fuel settings of 14.3:1 to 15:1 to one or there abouts.
So how does that work?
In closed loop the ecm trims the fuel based on O2 input. In open loop the ecm uses the stored fuel tables (maps).
OK so how does the ecm know when its in closed loop or open loop? If 14.6 is the entry in the look up table for the applicable cell, it tries to operate in closed loop. This is call the Air Fuel Ratio Switch. And its the reason why trying to trick the ecm with resistors in the O2 sensor circuit don't always work well.
OK enough of that.
Some of us don't like the way these scooters run as delivered from the factory, so we make changes. And most of that involves replacing the oem fuel map with one written to make better power.
So Harley says that the fuel targets should look more like this. 12.8:1 to 13.6:1
But wait, remember that narrow band O2 sensor, it can only function at 14.3:1 and leaner. How does this work. The way it works is that the ecm is reprogrammed to ignore the O2 sensor, and no longer trims fuel based on it. No cells in the fuel map will have 14.6 entered. So there is no closed loop operation.
Or, a devise is added to the system that allows for the use of Wide Band O2 sensors.
So what is a Wide Band 02 sensor.
Wow, it works sooty rich, 10:1 all the way to piston burning lean 18:1. So why the hell doesn't Harley uses these? Its simple, they cost more, and are not needed to keep the fuel at 14.7 to one. The $9.95 narrow band sensor can do this. But Harley will sell you what you need to install these sensors. Fact is, these very sensors can be used during the dyno tuning process.
So how does this tuning thing work? And why do I need it. You don't need it. Your scooter will run well enough as delivered. But if you want it to run better or change parts, you might need to have it tuned. There are three main ways it works. You can load an new map into the ecm, or flash it. This is what Harley does when you do a stage one. You can add a device to the system, or you can replace the system (ecm) Add on devices run the range of allowing you to load new maps (flash), build new maps on a dyno, or build new maps on the fly.
And there are two types of tuning. Using legal EPA approved maps that are within the 14.7 limits and still use closed loop function, or Race only maps that are not approved for street use by the EPA. Harley dealers are only allowed to install EPA approved maps. And that's all I'll say on that.
So now you have the basics.
In a nutshell, there are two types of fuel injection used on Harley's. Way back when, it was a Magneti-Marelli Alph-N system. And they had a lot of issues. Poor parts quality, limited processing power and most of all, poor tech training. This system was used to try to satisfy the EPA's demands for cleaner running motorcycles. And it did, within its abilities, and when it was in proper working order and properly adjusted.
A while later the EPA demanded that the scooters run even cleaner, so much cleaner as to include catalytic converters. The MoCo knew that the MM system was not up to that task, so they adopted a Delphi built Speed Density system.
Here is a power point presentation on the Harley fuel injection system and the tuners that were used to tune it. It predates the epa clampdown, so it includes a little info on the ways to tamper with the oem system
Electronic Fuel Injection for Harley
OK so here are some points from the presentation.
But first, I've added a couple of fuel table representations. Take note of the number in the individual cells. That's what is important.
The system uses pre installed fuel maps to determine how much fuel to provide under any given condition. Many of us have seen visualizations of these. There are many ways of presenting them to the human eye. What's important is the numbers in the cells. 14.6 is the target for closed loop fuel trim. 14.6 is the ratio of air to fuel. 14.6 grams of air per gram of fuel. A lower number calls for a richer mix (more fuel), and a higher number is a leaner mix (less fuel)
Notice how the table avoids 14.6, more on that later.
The MoCo has no choice but to attempt to target the fuel mix at 14.7 to 1. Its the law.
To do this, harley build the fuel tables and then uses a narrow band O2 sensor (Oxygen Sensor) to maintain the fuel trim. This is called closed loop operation. This is only available during idle and light load cruise conditions. The rest of the time the ecm just uses the apropreate setting from the fuel tables. This is called Open Loop. In open loop the O2 sensor has no function. And this is because of the limitations of narrow band sensors. They can only function at fuel settings of 14.3:1 to 15:1 to one or there abouts.
So how does that work?
In closed loop the ecm trims the fuel based on O2 input. In open loop the ecm uses the stored fuel tables (maps).
OK so how does the ecm know when its in closed loop or open loop? If 14.6 is the entry in the look up table for the applicable cell, it tries to operate in closed loop. This is call the Air Fuel Ratio Switch. And its the reason why trying to trick the ecm with resistors in the O2 sensor circuit don't always work well.
OK enough of that.
Some of us don't like the way these scooters run as delivered from the factory, so we make changes. And most of that involves replacing the oem fuel map with one written to make better power.
So Harley says that the fuel targets should look more like this. 12.8:1 to 13.6:1
But wait, remember that narrow band O2 sensor, it can only function at 14.3:1 and leaner. How does this work. The way it works is that the ecm is reprogrammed to ignore the O2 sensor, and no longer trims fuel based on it. No cells in the fuel map will have 14.6 entered. So there is no closed loop operation.
Or, a devise is added to the system that allows for the use of Wide Band O2 sensors.
So what is a Wide Band 02 sensor.
Wow, it works sooty rich, 10:1 all the way to piston burning lean 18:1. So why the hell doesn't Harley uses these? Its simple, they cost more, and are not needed to keep the fuel at 14.7 to one. The $9.95 narrow band sensor can do this. But Harley will sell you what you need to install these sensors. Fact is, these very sensors can be used during the dyno tuning process.
So how does this tuning thing work? And why do I need it. You don't need it. Your scooter will run well enough as delivered. But if you want it to run better or change parts, you might need to have it tuned. There are three main ways it works. You can load an new map into the ecm, or flash it. This is what Harley does when you do a stage one. You can add a device to the system, or you can replace the system (ecm) Add on devices run the range of allowing you to load new maps (flash), build new maps on a dyno, or build new maps on the fly.
And there are two types of tuning. Using legal EPA approved maps that are within the 14.7 limits and still use closed loop function, or Race only maps that are not approved for street use by the EPA. Harley dealers are only allowed to install EPA approved maps. And that's all I'll say on that.
So now you have the basics.