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[lonewolf55]

"The INTAKE AIR TEMP sensor tells the ECM the quality of the air."

You sure about that Doc1??
If the intake air temp sensor could modify the map for o2 content, why have o2 sensors?? How does a temp sensor measure the O2 levels at any given elevation when it is essentially a "thermometer"?
Not trying to be a wise a$$, just want to know?

There is a difference between quality and quantity.

[Doc 1]

The intake air temperature is one parameter used to fine tune the mixture.  Higher temperature air is less dense and thus there is less oxygen in the combustion chamber.  To maintain the AFR the map calls for, the ECM reduces the amount of fuel as the intake air temps go up, and adds fuel when the intake air temp goes down.  This along with adjustments for actual engine temperature, manifold absolute pressure (air pressure and load), etc. make up the basic ECM automatic adjustments to the mixture.  All of these are dependent on the accuracy of the various sensors used to collect the data for the ECM, as well as the capabilities of the persons doing the ECM programming.  This stuff is one big reason why EFI bikes don't need to be retuned for major changes in altitude and temperatures like the old carb bikes did.  But it isn't precise enough on it's own to assure compliance with emission standards, since sensors can drift and things like fuel pressure can change over time and air filters can become restricted, etc.  So the feedback loop (O₂ sensors) adds another adjustment to the mix, measuring the result of actual combustion and fine tuning the mixture again.  In more sophisticated systems, there is another sensor after the catalytic converter to make sure the converter is working.  Your Harley doesn't have that yet, but I imagine it's only a matter of time before the EPA and CARB start requiring that as well.


Jerry

Very well said Jerry.....I could of sworn I said the same thing twice in this thread.....lol...lol
Doc

[SIX38]

I love this site. What better experts to answer my question but the combined talents of Doc & Jerry. Great information. Simply put, air at higher elevations is less dense and therefore carries away less heat. Engines will then run hotter. I got it.
 Being in the HVAC business I should have known this, but having spent my entire working career at less than 1500 feet, the issue never came up. But as they say, one is never to old to learn.
Thanks again,
Tom P.