1996 tahoe wont start

There should be a 2 second prime by the fuel pump. This prime by the fuel pump is standard for GM vehicles, and if it is not present a hard start is encountered. Turn the ignition to the run position and listen for the fuel pump operation. You may have to have an assistant listen at the fuel filler by installing a long slender funnel into the fuel inlet to the tank, remove the gas cap and insert the funnel, listen at the large end of the funnel to see if the pump can be heard running. Using the funnel acts like a megaphone and makes it easier to hear the pump. If the pump runs for 2 seconds after you turn the key to the run position (DO NOT attempt to start the engine during this test) and the engine doesn't start due to lack of fuel, check for an obstructed fuel filter. (Just change it, it's probably overdue for service anyway since everyone thinks it get changed during oil changes, but never really does.) If the pump doesn't run during prime interval, the computer may not be turning on the fuel pump relay, or the relay is defective. To check the relay, use another of the relays in the power distribution box to substitute for the suspect fuel pump relay and retest. Be sure to wait at least 30 seconds between key cycles since some systems have a delay timer built in to keep the pump from over running. Be sure the relay you sub into the fuel pump socket is identical to the one you remove and properly oriented in the socket. The engine will run following your manual prime because an additional set of contacts in the oil pressure switch will power up the fuel pump relay once proper oil pressure is achieved by an idling engine. If you find that the relay is not defective, but doesn't provide a priming impulse, the engine computer may have failed. DO NOT use a conventional test light with a filament type bulb to check any of the computer circuits that drive the fuel pump relay, or any other computer controlled circuits on an automobile ( or pickup) The driver circuits in a vehicle computer can be blow-out by over-current when using a conventional test light. You can use a high-impedance DVOM for testing safely.