My Jimmy (99 SLT 4x4 165k miles) randomly looses engine power while driving and resets to a state as if I had turned the key on but never started the car. In the last 2 years trying to figure this problem out ive replaced the fuel pump and inline fuel filter(3 of these) including the recall for the fuel pump pigtail, intake pressure regulator, cap and rotor, plugs and wires, ecm computer, spark control module, oil pressure sensor, radiator water pump and thermostat, battery and cables ground line and cruise control blinker module. The car was just in a shop for a week the drove it around and were easily able to duplicate the problem but the scanner registered nothing other than the engine was off there are no codes or pending codes. This problem happens on smooth roads rough roads or waiting on the light to change but not sitting at an idle. Fuel rail pressure is oem spec cat is good timing is good jigling the key cylinder does not make it happen and no one can figure this out please i need help

 

Did You check the column electric ignition switch? It seems to be a common problem...

 

Are you talking about something differnt than the key cylinder?

 

Do a good long alternator test? A momentary hiccup in power output could cause it to lose spark

 

Nop, I mean this one. If the connection is lost there, it will not throw any codes (same as it doesn't when You switch the ignition off by using a key).