As the mystery of the new EFI bikes become unraveled and performance opportunities explored, few subjects of discussion are as debated if not misunderstood as air Injection as it relates to electronic fuel injection (EFI). The carb boys have a lot of experience with removing it on their bikes and know that it has no affect on A/F ratio. Some believe removing AI upsets the temperature of the O2 sensors on EFI. It doesn’t. EFI changes things but not as much as some believe. AI and EFI are almost independent entities made to work together but not dependent on each other. EFI doesn’t want or need AI to operate effectively.
AI in fact needlessly complicates things and hence for a hotrodder, many of us being card carrying members, AI simply must go and what this thread is about.
There are two types of air injection widely used. On automobiles, a compressor is used which has different functionality than pulse air injection widely used on new closed loop EFI motorcycles. Pulse AI gets its name from the engine firing and exhaust pulses. When pistons go up in unison on a vertical twin for the exhaust stroke, this creates an air percussive pulse (wave) out of the combustion exhaust ports with velocity and momentum based upon no. of pulses per minute i.e. one half of engine RPM e.g. 4 cycle. In a closed volume, if an open orifice is upstream of this exhaust wave or pulse e.g. air injection tube….with a fresh air source available e.g. airbox, this draws...due to vacuum ...not injects (which would be positive pressure) air into the injection tubes which then is drawn into the headers to join the flow of pulsing exhaust air being emitted from the exhaust ports. So air is really drawn by vacuum into the air injection tubes, not injected under positive pressure per se…hence air injection is really a misnomer. This additional cooler air supplemented to expulsion of fuel from the exhaust ports into the headers when the throttle is closed in combination with hot headers due to combustion creates a more complete burning of fuel for reduced emissions.
The ECM only energies the solenoid to allow air into the exhaust ports at small throttle openings but also senses its presence by virtue of it solenoid resistance. The solenoid registers 20 ohms of resistance when measured with a multimeter. Without a complete circuit with resistance, the ECM will throw a code and initiate a check engine light (CEL). Both an open circuit and shorted circuit have been tried and each result in a CEL on the new EFI bonnie.
Some inquiring minds may want to know how substituting a resistor satisfies an ECM. Pretty much all interfacing components with the ECM are either fixed or variable resistors. This is how the ECM processes its information. A solenoid is a linear motor with an electromagnet comprised of a helix of wire...in effect, a resistor not unlike the ceramic covered wound wire resistor used for this DIY to replace it. Difference is is how the energy is dissipated. Basically an ECM is a microprocessor with a number of integrated MOSFET’s. MOSFET’s are semiconductor transistors used for voltage comparator circuits. ECM’s contain thousands of these decision making devices. The way AI works is…the the TPS tells the ECM the rider has let the throttle return to idle. O2 sensors go into open loop and don’t talk to the ECM which defaults the A/F mixture to a baseline map based upon information from the air temp sensor. The TPS in idle position causes the the ECM to send current to the solenoid...about .6 amps…to engage the valve and draw air from the intake into the exhaust ports. During this time the ECM evaluates the voltage due to change in current and compares it to a programmed upper and lower limit based upon MOSFET selection. If the voltage is too great or too small, it will gate the current to deploy a CEL and reset the A/F map to limp mode or open loop. That is how a circuit can both operate a solenoid and also simultaneously detect proper amount of voltage for upper and lower limit. By substituting a resistor, the circuit when activated by the ECM will still compare voltage however will no longer effect any mechanical change i.e open a valve…as the ECM interprets the resistor as a solenoid. A simple calculation suggests that a 50 ohm resistor will reduce current to .24 amps = 2.88 watts of power which will be dissipated in terms of heat versus work done to move an electromagnet opening the valve. Choosing a 10 watt 50 ohm resistor, not only reduces current still acceptable to the ECM, but also emits a modest amount of heat energy easily contained by the relatively large heat sink based upon its intentionally oversized 10 watt thermal mass capability.
OK…how to remove AI from EFI bonnies:
To begin…Richard and Dick need to be credited with a DIY to remove the gas tank on EFI bikes seen here:
Further, Dick is to be credited with the first to my knowledge to both remove AI and add a Power Commander III to a new EFI bike…Dick has two new EFI bikes in this configuration in fact. So Dick really started the ball rolling with removing AI initially. One of the things we have learned since then is…you don’t need a Power Commander to remove AI. Many owners started taking the AI’s off EFI bikes either with the base map or one of the optional maps. Some got CEL’s because they went a step further and removed all the plumbing associated with AI including the solenoid. I like clean so that means all the plumbing must go.
Let’s get started.
First remove the tank…how it looks with the tank off and AI plumbing in place
Most of the stuff shown in the picture will be removed:
Next unplug the large hose that draws air from the air box.