How to verify your Megasquirt tune is homing in.


New Member
Mar 22, 2011
Las Vegas, Nevada, United States
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*Author - John Whittle

At the most basic level, an engine management system tries to control the injection of fuel and the timing of spark to allow for proper functioning of the engine. For the fuel injection component, the EMS uses various sensor inputs and applies an algorithm, or a series of mathematical processes, to estimate when and for how long to hold an injector open. It does not directly "know" how much fuel is released, only how long it held the injector open (assuming there are no electrical or mechanical faults, this directly translates to an amount of fuel).

The job of the Electronic Management System (EMS) is to guess how much air (and by extension, oxygen) is getting into the engine and then hold the injector open for the correct duration to release an appropriately timed and correct amount of fuel for the desired combustion characteristics (economy, power, detonation resistance, etc...). The EMS has to guess because it is (currently) practically impossible to measure the amount of air that actually makes it into a cylinder under all conditions. The goal is to get the VE table to generate and AFR out the exhaust as close to the target AFR as possible. Se the following two screen shots. The are essentually the Fuel VE table and the results as measured by the wideband sensor.

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