1999 Pontiac Grand Prix GTP starts, then stalls. Fuel pressure fades.
See update at bottom for this question previously posted.
The first stall actually occurred while driving on the highway at 110KMH (65MPH) after 20 minutes running with no problems. Had it running about 1.5 hours on highway prior to that, again no problems - no indication that anything was about to go. Restarts ok, then stalls again in a few seconds. Can't get it to stay running any longer than this. Almost like running out of gas, but tank is half full. After towing home, checked fuel pump at trunk access panel and sounds like it is running with key on. Checked fuel pressure release on top of engine on fuel rail, fuel seems pressurized and squirts out. Opened gas cap, no vacuum or pressure build up there. No broken belts, no idiot warning lights on. Gauges and other systems appear OK. Battery new 9 months ago. Fuel filter, plug & wires replaced 12,000 KM (8,000 miles) ago. Using premium gas from same company. Car has 270,000 KM (160k Miles). No recent maintenance other than oil change 2 months ago. Any ideas on what else to check?
ODB 2 scan shows no problems. Would not a bad crankshaft sensor be picked up here?
Fuel pressure is 55 PSI with key on engine off, while pump is on, then slides to 48 when pump shuts off and holds steady there with no further loss of PSI. Start car, PSI gradually drops to 0, engine stalls. Fuel pump comes on again at engine stall and PSI returns to 55 PSI, sliding to 48 and holds. Replaced fuel pump relay as thought this may be cause for fuel pump not on during engine run, no change.
Almost as if fuel pump will not work while engine on...
Comments & suggestions appreciated.