| ""For example, one location on the VQ table is 2 volts. The next higher location is 2.08 volts. So there is a margin of .07 volts to work with. In other words, the MAF voltage output can be between 2 and 2.07 volts and it's still going to put you in the same table location. You can have an inaccuracy of .01 to .07 volts and it doesn't matter. "" I'd have to disagree with that. From what I've seen in the ECU code, it reads the two adjacent VQ table values and linearly interpolates between them. An inaccuracy of 0.01V definitely matters in this case and results in a significant error in the interpolation. the interpolation is calculated as follows: VQ = VQ1 + (VQ2 - VQ1) * (MAFVolts - V1) / (V2 - V1) where:
VQ is the interpolated airflow value
MAFVolts is the MAF sensor voltage
VQ1 & VQ2 are the adjacent VQ table cell values
V1 & V2 are the corresponding MAF voltages for those cells
plugging in the actual VQ table values for a MAF voltage of 2.01v:
3514 + (3968 - 3514) * (2.01 - 2.0) / (2.08 - 2.0)
3514 + 454 * 0.01 / 0.08
3514 + 454 * 0.125
3514 + 56.75
VQ = 3570.75 and for 2.07v:
3514 + (3968 - 3514) * (2.07 - 2.0) / (2.08 - 2.0)
3514 + 454 * 0.07 / 0.08
3514 + 454 * 0.875
3514 + 397.25
VQ = 3911.25
Since the VQ value is then used to calculate TP (engine load), any error in the MAF voltage is going throw off how the fuel and timing maps are indexed (among a lot of other things). This results in the wrong ignition timing and target a/f ratio being used for the actual engine load.
- Sam |
23:11:06 06/28/16
