need help, 4AGE started to run really rich, need to know why

[blownmiata91]

Quick recap of the engine
Toyota 4AGE 16 valve DOHC big port red top
264 degree cams
Haltech Elite 550 ecu
Denso coil on plugs
Miata 1.8 injectors (tan) 230cc cleaned and bench tested 3000 km ago
BMW TPS

The car was running great. Plugs were tan colored. The only issue was a high rpm misfire (only on the track)
All of a sudden, it started running really rich, struggling to run at part throttle between 1500 and 2500 rpm in first and second gear. Clears up at 3000 rpm and pulls like a freight train.
I am reluctant to remap the fuel until I find out the cause of the problem. Plus, the soot has clogged up the O2 sensor and I don't want to waste money replacing it until the problem is rectified.
The ecu says there are no trigger issues with the cam angle sensor in the distributor or the hall effect sensor on the crank trigger wheel.
fuel pressure is normal. I replaced the fuel filter.
Suggestions????
thanks
Doug

[jondee86]

Vacuum hose to the FPR fell off or split ?

Cheers... jondee86