96 bonneville - random misfire

I first noticed problem while driving on a freeway at 75mph. When I tried to accelerate the engine stumbled. if I let off accelorator and then press peddle half way to floor it would accelorate. The obdII code said cylinder six misfire. Also engine was running cold, and had cooling fluid on back side of engine--not good.

Here is what I have done so far.

replaced cooling thermistat and temp sens. Still was not reaching operating temp. Did a pressure check of the cooling system and that reveiled a plenum gasket leak. So, I replaced the plenum and intake gaskets. Now the engine is running at operating temp consistently.

BUT, I the engine misfire migrated to cylinder 2. The only thing I didn't do when reassembling the fuel rail was to keep the injectors in the order, I mixed them up. So when the misfire migrated to cylinder 2 I replaced that injector. Problem still exists. Have also done a complete tune up. plugs, wires, pcv, fuel filter etc. I also switched coil paks around the misfire did not migrate to a different cyliner.

Did a fuel pressure check. when key was turned on pressure was between 42 and 47 psi. Also fixed any vacuum leaks found.

any suggestions would be greatly appreciated.

Repost this in the Pontiac forum, more help there.