Do you have to lift the motor on a Pontiac grand prix 6 cyl. to get to the back freeze plug that is leaking oil?

This could be a freeze plug or the water pump has failed,

2002 Grand prix expansion plug

might be cylinder head gasket leaking to combustion chamber,small leak that it can sip into combustion chamber and burn but the coolant will not burn completely so will stick to spark plug and cause miss fire.

Bad coil pack possibly.thats the three square things near back of motor .plug wires go into it.

I believe that both 2 and 6 cylinder show up as cyl 2 on the diagnostics tester. so you will need to check the wire and plug for both cylinders.

Check the rear head, head gasket.I think that this may be your problem. I`ve experienced this before in my shop..
You can also take your car to your repair centre for a visual check. Most shops will charge about $50.00 for this service/inspection..

Do you see the coolant leaking on the motor? From the drivers side, you can inspect the intake manifold...unfortunately as good as this motor usually is...it is known for leaking at the intake manifold...and requires a new intake gasket...DO NOT USE dexcool after the replacement...many teams believe the dexcool is part of the problem...use the coolant that "For All Coolant Systems" is still the green anti-freeze...Hope this helps.

spark plug gaps are very critical on computerised cars!! [some wont even start!]
distributor module may be breeaking down as temp rises they fail!
otherwise do compression check as it may have valve problems
also check plug leads & injectors aswell as the fuel pump pressure [ could bestarving for fuel]

the fan motor could just be bad, you can test this by removing the fan and connecting a wire to each terminal and to a battery. the wires hooked up one way will spin the fan and the other way will spin the fan backwards so you cant hook it up wrong. I hope that helps you out!

Try some motor honey. It can be bought at most part stores, advanced auto, autozone, ect. It worked for my 95 Grand Am when I had a leak in my oil pan gasket. Hope this helps