Weird coolant problem and misfire

[GunMetalGT]

I just got a 98 Grand Prix GT 3.8 about a week ago. When I got it home it was overheating and misfiring so I changed the plugs and wires with duralast wires and acdelco plugs and flushed and replaced the dex coolant with green after making sure all the orange was gone and replaced a broken elbow with an aluminum one. Drove it around the backroads for about 20 mins. Didn't overheat but was still misfiring like crazy. Let it sit for an hour to run to town and when I came back all the coolant was gone. No visible leaks around the rad, the water pump, elbow, floorboard, or the ground. So here is where it is now. Coolant is going somewhere unknown to me and it is still missing on cylinders 3 & 5. Any ideas on what it could be? Any advice would be greatly appreciated.

[Fivefingerdeathpunch]

Possible UIM/LIM gasket failure, if the coolant is not on the ground and is missing, the motor is eating it.

[GunMetalGT]

Thanks. Shouldn't be too hard right lol That would also cause the misfire on 3 & 5 right?

[Fivefingerdeathpunch]

Maybe, or a possible coil pack as 3/5 are on the same coil. You could swap them around see if it follows a coil.

[GunMetalGT]

Update: Changed the LIM gaskets and swapped out the radiator which fixed the coolant leak. Changed all the coil packs and still getting a misfire. not near as bad but its still there. Also, my low coolant level light now comes on even though the rad and overflow are full. What could cause me to still have a misfire? It now has new plugs, wires, and coils.

[mguzzo]

did you clean the sensor? and plug it back in?

[GunMetalGT]

that I have not tried. will do that