Checked the fuel pressure this morning on start, idle, revving the engine above 3500 RPM, and then took it for a test drive to produce the rough running problem (which only happens when the engine is under load - I cannot produce the problem by just revving the engine while parked). Once I was able to generate the problem where Inj 1 is shutdown by the ECU, I checked fuel pressure again. In all scenarios described above, fuel pressure sits at 50 psi, so, I do not think my issue is fuel pump, or fuel filter related. As mentioned both fuel pump and filter are not that old.

One thing I DID note using my Torque app; while the rough running/injector 1 shutoff occurs, the voltages from all O2 sensors is 0 (i.e no up/down oscillating the way they do normally), so whatever is going on, it appears the ECU not only turns off injector 1, but the feedback loop from the O2 sensors is also disabled by the ECU (?). When I erase the ODB codes the injector is turned back on by the ECU, the O2 sensors are also back online. I am curious to know which came first, the injector shutting down, or the sensors being turned off (assuming there is some relevance between those two elements).

Compression test is next in the queue.....