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the ECU reads the MAS voltage, then divides it by 0.08. The 'number' it gets is the number it references the VQ_Table with, which is a table that accounts for the non-linearity of the signal from the MAS. Then here's the forumla it pumps the information into. ((VQ_Data * Injector Size) / (RPM / 50 * 256)) / 6 the value given at this point is called the TP, or theoretical pulsewidth. The ECU is calculating the volumetric efficiency with this forumla. The TP value it gets is the engine load. From this point, the ignition timing subroutine plugs the current TP and RPM into the ignition timing map and the point on the map that those two values intersect is the ignition timing in degrees BTDC. The same thing is done with the fuel maps, but the data point represents enrichment above stoichiometric. Remember, since the ECU knows how much air has entered the cylinder via the forumla I just showed you, it knows exactly how much fuel to inject to make the mixture a perfect 14.7:1. The map is simply a revision map that allows you to specify enrichments from this point. The ignition timing map states specifically what the ignition timing is for every point. The ECU does not calculate a theoretical ignition point. There is a knock zone in the ignition maps, but that doesn't make the ECU guess or calculate what the ignition should be, it only tells it to refer to another map if it detects knock. So when you say that timing is calculated from the MAS, you are correct, but probably not in the manner that you were thinking. The MAS is the primary sensor used with our ECU's to handle these functions.
: among other things. My turbos pull the extra air to register the timing.
[ ashleypowers.com ]
[ agpowers@bellsouth.net ] When pigs dance, you better get it on video...
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