3800 misfire HELP???

[Derty2009]

I bought a 1997 Grand Prx gt and it blew up the next day. I put a new engine in it and now there is a problem. It runs like a champ when it is cold. It pulls hard and everything but then when it warms up it misfires and chuggs like crazy when its under load. It is reading out 2 codes. One is misfire in one or more cylinders and the other is a bad o2 sensor. The sensor was bad when my old engine was in and that one ran fine. Please help. I hope its something easy. Also my gas guage is screwing up. I dont know if that is due to the problem or not.

[Liquifire]

which o2 sensor? the front one is far more crucial.........if that one is bad, replace it ASAP. I believe the gas gauge info is being sent from the gas tank sending unit IIRC?

[Derty2009]

It is the o2 sensor on the manifold. I also have one more question. When I was hooking up the main harness to the tranny there was i think 3 plugs. 2 of them were big and hooked up into the solenoids on the tranny but the last one is small and I dont know what it is or where it goes. Any ideas?

[Liquifire]

if your front o2 sensor is not working correctly, it is critical that you replace this ASAP......not sure on the wiring issue...can you get a pic of the wiring harness that you are referring to? it would help a lot.

[blueguy]

Replace the sensor...get new plugs/wires and check the coil packs/ICM.