I have a Pontiac Grand Prix 2001 model it starts up and runs good for about three or four seconds and then dies as if I turn the ignition off why is it doing that

possible your fuel pump is going, need to have it pressure tested, i would also look at the throttle body, it may need to be cleaned.

The fuel pump was on my mind I took the Jon Jones dealership yesterday they hooked it up and done a diagnostic test on it they thought I had the wrong key for the car so they sold me a key that has a chip in it it didn't work so now they're going to give me a free diagnostic test in the morning but I think it's the fuel pump because it starts up three four seconds runs idles great then just dies

The Ignition has a Resistance wire in your Steering Column. Look under dash for wires going to square block connector. Look for 2 wires inside a ORANGE loose covering. Take that Key they sold you cut the Orange- 2wires going to column strip wires and put a wire on each side of that resistance chip and Start your car. The resistance chip in that key makes your fuel pump stay on if you got Tilt wheel that wire broke. Or gm can tell you the resistance frequency & go buy a resistor wire it in. It will start