The injector leak down response has slight credibility based on some reading I've done, though I've never seen injector leakdown keep a Honda from starting.
I'd suggest doing
a injector leak down test and swapping the two upstream sensors to see if the negative trim follows the sensors.
Not exact matches
I suspect I have an EFI common rail
injector that fails to hold pressure and slowly
leaks petrol into the manifold when the engine is shut
down (and possibly while running).
I had no idea what OBD1.5 was until I bought my 95 Explorer Conversion Van but I guess I lucked out because it has saved me countless hours of diagnostic time tracking
down weird problems like a
leaking injector hose (inside the bread loaf upper intake manifold).