Got a crazy one here for you that has me at my wits end. Mazda engine, 2.2L F2 with the non common fuel system with the trim injector and the ECM upside down mounted on the side of the truck frame under the intake. have been through everything in the last 3 months and have run completely out of ideas. I know with the main fuel port off, the unit should run off the trim injector, this one will not. when running if you partially cover the intake horn with your hand, the O2 sensor climbs as it should. we have used a calibrated exhaust analyzer to confirm, as well as a good plug reading that the engine is in fact running lean. the original technician swapped put the LPG converter, and disassembly of the original and replacement converter show no issues or concerns as output vapor fuel pressure is 4 PSI.. The intake plenum is free from obstructions, and no intake leaks as pressurizing the intake manifold to 15 PSI. with all the valves closed, have checked and adjusted all valve clearances, removed the head and had a few valves replaced due to soft sealing from carbon build up. compression is a good 180PSI across all 4 cylinders, and 5% leak down. the exhaust is free from any obstructions, cam and crank timing quadruple checked as well as making sure the crank gear has not walked on the crank shaft and is at TDC 0 degrees. ignition timing and sequence is correct as well. We also threw a hail mary at the electronic governor believing maybe it was open farther than it should be. its as though the engine is drawing too much air in the intake, the injector is unable to supply enough fuel even when bypassing the ECM pulse control and giving 100% open fuel, its running off the main fuel that is only supposed to feed when applying throttle, creating a vacuum draw to open the main fuel flow, the fact that this is supplying the fuel to run the engine tells me that there is too much air moving by the upper throttle body to activate the line. Map sensor reading 14 engine off, 6 running (normal) Yes, we also swapped out O2 sensor, and trim injector with no effect. the last attempt was to soak the cylinders with TOP fuel engine cleaner for possible stuck rings (automotive days with GM). Can throttle up, but stumbles off of idle as its already drawing fuel from the main line. We are at the end of the line where our only thought is to swap out the entire system with a regular system, yes, the ECM, engine harness, intake manifold, everything. anyone have any ideas?