The OPS on the china rail is a backup to the ECM turning on the fuel pump relay by bypassing it. When it sees ~4 PSI, it'll turn on the pump too. Anyway, the OPS is directly plumbed in to the oiling system. This drawing is for an 88 but it's good for VIN Z (4.3L) too. Again it's for an 88 but, the 2 years are almost the same other than dash and gauges.I'm SO confused. The fuel pump doesn't pump oil, why would it have a switch for such a thing?
See if the EGR valve is holding vacuum.