1997 grand prix very ruff idle no power changed cps and checked injetors and fuel pressure was 46-50 psi. have great spark to all cylinders

You need to make sure the cylinder is getting fuel and that it doesn't have a vacuum leak at the intake that is leaning it out and causing a misfire, if that checks ok then determine if the #4 cylinder has acceptable compression as compared to the other three, all cylinders should been within 5% of the cylinder with the highest pressure on test.

Check wiring harness around and including plug to the coil pack. Also check fuel pressure with vehicle running. I'm not sure of the specs but, Iit should be around 35 to 40 psi. at idle, and 50 to 75 at higher RPM's. I've seen Fords run with a bad fuel pump and demonstrate these exact symptoms

Someone will need to check fuel pressure at the rail, and see if the injectors are getting power and a ground pulse from the computer.

Definition of Diagnostic Trouble Code P0300 Category: Powertrain Definition: Random/Multiple Cylinder Misfire Detected

Change the crank position sensor

check all fuses for turn signal and brake lights.change fuel filter . first. do a little tune up change spark plugs and wires . if changing fuel filter dont help. have fuel pressure check first before buying a new fuel pump .they run after taxes 400.00 dollars. your fuel pressure should be 41 to 47 psi. replace fuel pump relay also.

if as soon you give gas it dies i would check the gas pressure it should be about 50 psi if it good check the compression on that cylinder thats a start let me no

Heres what you need to do to start with. If you are mechanically inclined, when it stalls, check for spark on the #1 cylinder. If you have no spark there, it is likely the CPS or Crankshaft Position Sensor has gone bad, a common issue, and will need to be replaced.

If you need any further help, there is an online Grand Prix community you can check out at http://www.grandprixforums.net. Sign up there and post up your issue and you will get some more input.

With the 3.1 engine: Ignition on 52-59 psi, at idle 42-56 psi. With the 3.8 engine: Ignition on 48-54, at idle 38-51. Let me know if your's is supercharged the specs maybe different.

have you replaced the fuel filter if you have may have a problem with the exhaust being plugged if you haven't replaced fuel filter try that