91 Lumina won't start after fully warmed up

[Electric_mouse]

Starts and idles good cold. Idles a bit rough after running several minutes, drives ok and will restart but if left for 15-20 minutes refuses to start. After parked for few hours it's starts fine again.


Replaced ICM and coils with bone yard ICM/coils. Spark tester connected to 6th cylinder (easy to access) indicates spark at all times. Didn't check other wires but did reroute the rear bank. Doesn't appear problems there.


CPS next step? (8th digit in VIN is T) Where is crankshaft sensor on this engine?


TIA

[maxwedge]

Tough diagnosis, leaking injectors, poor crank or cam sensor signal, skewed coolant temp sensor. No one answer here. Also, when you know the start problem is imminent, hold the gas pedal to the floor while cranking, this is the " clear flood" mode.

[Electric_mouse]

wave form of crankshaft sensor, cold with no spark plugs installed. Not the clearest. Will try for a better pic. It's been a year or more since I fired up the scope so bit rusty getting a capture.


Timing pulse followed by five more for remaining cylinders.


Next step will try to capture the pulses when engine is warmed up and fails to start. It takes about 15 minutes after shut down and will fail to start. Then it's 3-4 hours for the engine to start again.


BTW I built a noid light and #1 cylinder is receiving pulses.


If anyone is interested the noid light is very easy to build. There are YouTubes but my design doesn't require polarity.

[Electric_mouse]

BTW yes fuel pump is 40 lbs