1990 Chevy Lumina Cuts Out

Starts and idles for a few seconds and the cuts out. Can’t step on the gas cause that cuts it out immediately. Mechanic replaced the fuel pump, fuel filter, and computer. He told me the electrical signal to the fule injectors starts and is strong and then the pulses just die down.

This can be caused from a faulty crankshaft position sensor. Have him check the resistance for the sensor to see if it’s within specs.

Tester

The mechanic you have knows how to change parts; but, does he know how to troubleshoot? Does he know how to use basic tools, such as: a vacuum gauge, compression gauge, electrical multimeter, etc?
If Mr. Mechanic can use a digital multimeter, let him check the sensors, and control valves (idle air control valve, etc.) with it. The instructions, and desired values (ohms, volts, freqs) of the sensors and valves are in the repair manual. One, or more, of these components has incorrect values.