My AJ6 engine is dropping power when it warms up. Every time I drive it and while still cold, it reminds me of how “nice” the car’s acceleration feels, but the party’s soon over after it warms up. This is actually “confirmed” by my wide band Air/Fuel Ratio gauge (A-pillar). Just yesterday, at WOT, the gauge read 12.5:1 cold, which is good WOT AFR for a cold engine but 10.3:1 hot, which is insanely rich and which is why power drops so much. But then, if power drops when the engine warms up it means that, somehow, the rise in engine temperature is not being correctly reported to the ECU, therefore the ECU believes that the engine is still cold and it keeps feeding fuel to the cylinders at a “cold-engine” rate, i.e. “rich” and down goes the power. First suspect, the coolant temp sensor? Nah, it reads 260 ohms almost fully warmed up (190 F to 200 F), which is fairly close to the sensor resistance called out by the temp table in the manual. Other than that, I can only think of a possible oxygen sensor lying to the ECU, but the OEM oxygen sensor is not a wide band sensor, so it can't really be "read" the way my gauge sensor can, as it is a wide band sensor feeding the AFR gauge from a 0 to 5 vdc proportional to AFR and a reading on the gauge that I know is good, as it typically reads around 14.7:1 (stoichiometric) during normal driving, so the O2 sensor issue can only be resolved installing a new sensor. It doesn’t occur to me what else to test, or how could the fuel be adjusted in the manner a carburetor can be trimmed, although removing fuel via other methods, and if that was possible, could also affect the cold AFR which is fine now. I know that there's much more to what the ECU does and I do need to read and learn more, but if anybody can think of something I’m overlooking, Id appreciate it? Thank you.
Cheers