I've had this issue for a year now, where the ECU would go into open loop and then dumps fuel (AFR <11) on partial throttle acceleration or intermittently when cruising above 80mph. It will continue to stay in this rich condition indefinitely until I ease off the throttle. This can occur under stock atmospheric conditions (intercooler pipes disconnected, all MAP voltage clamping devices removed, basically a stock setup as far as the ECU is concerned).

Car drives fine otherwise. No hickups/stumbling. New MAP, O2 front sensor, TPS, coolant sensor, VSS.

I have been logging via the OBDII port. My logger states that the car goes into open loop because of "engine load/deceleration." This is not the same open loop state as when I start the car ("warm up" open loop).

I've logged the engine load parameters and the engine is not even over 40% load when the switch to open loop occurs. The vehicle never did this before even at much higher engine loads. I checked the contributors to engine load calculations (RPM and MAP readings) and they are not showing any noise. I checked the OBDII speed output and it says the VSS is constant when the switch to open loop occurs (I wanted to make sure noise in the VSS signal was not causing the switch to open loop).

In short, I cannot find a single parameter that changes when the ECU decides it's time to go into open loop. I have no idea what could be precipitating this. The only sensors I have not replaced are the cam, crank, and ping sensors. But I see no evidence that they are at fault.

It's REALLY annoying. Any ideas?

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO