what is auto-tune- how do it know?

The key to this are the o2 sensors-
Other sensors give data to the ECM of what conditions to expect - temperature, speed, rpms, air density [how much oxygen is contained in the air] etc.

the ion sense ( via plugs and wires) can tell the ECM how the mixture is burning in the cylinders


The o2 sensors tell the ECM the result of the combustion- how much oxygen is in the exhaust gasses and whether each of the cylinders is making a complete burn of fuel- this is the auto tune

- the o2 sensors may not always be active- common on many models is to revert to maps ( pre-calculated data points) when the motor is cold ( o2 sensors have to be over 600º to work) or at wide open throttle

the o2 sensors provide voltage based on the gasses flowing by, a complete perfect burn will give a value of .5 of a volt DC.
a too-rich mixture will be higher- to a range of 1 volt
a too-lean mixture will be lower to a range of .1 or even zero- especially in the case of a failure.
Either of those extremes is likely to trigger a code, CEL or limp mode

in real time the ECM is measuring the voltage from the o2 sensors- it knows which cylinder it is getting results from and can/will alter both fuel and spark timing for each cycle based on the results from the previous cycle of the motor --- fractions of a second

and the ECM will attempt to keep each cylinder burning so that it gets the perfect .5 VDC result...if it sees .42 VDC it may add a little fuel ...if it sees .58 VDC it may take a little away compared to the previous combustion cycle

in general a more retarded spark will give more torque, but use more fuel and burn dirtier- a more advanced spark will maintain a cruise and burn cleaner with better economy- to a point.
so when we cruise the spark advances as much as possible and the ECM looks for problems such as a misfire or pinging.
misfire can be a physical problem such as valve not opening or closing at the right time or it can be a engine management problem both too much fuel or too little fuel can cause a misfire

pinging is pre-ignition where the mixture does not burn evenly and controlled in the combustion chamber but part of the mixture explodes- this can be cause by heat- even a sharp surface in the head or carbon deposits acting as a glow plug or by a too lean mixture or by too-advanced spark timing- the plug fires before the mixture is properly compressed.

the ECM looks for these and will try to solve by changing spark timing or fuel delivery.



The pre-2007 H-D models did not have o2 sensors- the ECM relied completely on maps in which calculations were entered by engineers that if
at x rpm at y speed at z air density if we add fuel and spark in a specific way then we "hope" the cylinder burn is correct.
users settings in aftermarket "tuners" or a bad sensor could cause the motor to run poorly ( and some of those guys were running soot out the back- too rich, hoping for the best...but too rich doesn;t make best power either).
Even HD corporate was using o2 sensors on other bikes- like the Buell...and o2 sensors had been available on cars since the late 70's

so post 2007 we have a system where the ECM can sense the result in the cylinder of it's calculations and make adjustments.


so we all have bikes (post 2007) which "autotune".

of the aftermarket "tuners" there are a couple of ways to alter what the ECM is doing.

The simplest is a device like the nightrider.com xied/vied - I used these for over 5 years on my bike.
these are a resistor which plugs in between the o2 sensor and the ECM, they reduce the amount of voltage from the sensor slightly...the ECM reacts by slightly adding more fuel to get the expected .5 VDC that it wants to see- these fool the ECM taking advantage of the autotune
- the rev limit remains the same- and the bike uses maps when cold or WOT- these work best at part-throttle and cruising on motors which are not internally modified.

these are other devices which are more complex and will plug in between the bike wiring harness and the ECM- these can take input from the sensors and skew or alter sensor input by adding or reducing voltages so that the ECM reacts in a calculated way- similar to the xieds/ vieds we are fooling the ECM into delivering an expected result.
This requires that the person determining the settings be pretty smart and understand how each of these works and the possible knock-on effect.
With a double handful of smarts these can be set up to take advantage of internal modifications, cams, heads, compression, displacement etc etc- and probably better results will be gained by those which do use the o2 sensors and use the auto-tune principals.
A "download" or "flash" to the ECM ( usually by a dealer) will load in a different kind of map which will interpret the sensor data in a different way that the maps on a stock bike- these are calculated ( somewhere by someone) to make better use of internal ( cams, heads, compression, displacement) or external changes ( intake/exhaust)
There are also complete replacement aftermarket ECM's which may be more flexible or allow for wider variations in motor mods



o2 sensors are invaluable for determining what is happening in a motor and I have used these to tune my old Cadillacs, Panheads, Evos and even my Honda Trail 90...I get an o2 sensor into the exhaust and use a voltmeter ( sometimes taped to the bars) to see if how I am burning and adjust mixture and timing to get the best result I can given the constraints of carbs and points


fueled by coffee- Mike

 

very cool....thanks

 

Good info - keep that coffee pot on, man