It's not just fuel trim. There are timing maps that also change ignition timing based on temperature or other parameters. Super annoying, and terrible for getting a consistent "good tune"
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Originally Posted by DannoXYZ
That's fuel-trims causing shift. ECU has pre-programmed maps and target AFR. Using a piggyback to "fool" the ECU by modifying MAP/TPS values tricks it into injecting more or less fuel only temporarily. That's because ECU will analyse O2-sensor feedback to see how mixture is burning. If measured AFR doesn't match what's programmed, ECU will adjust injector duty cycle up or down until it does match.
So it's best to re-program the actual ECU maps themselves.
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