I have been dealing with the same #4 misfire on my 2000 bonneville after blowing 1/2" of head gasket between #4 and #6. I replaced the gasket and now have a #4 misfire. I installed a new head with new valves and springs, still there. I notice it idles good until a few seconds later then it misfires. When I pulled the old head, The exhaust valve on # 4 was black, the others were white. I am still fighting this mess. I had compression checked at the dealer and came out to 90. No burning oil, so I am guessing the rings are good.

I just joined this site, and cannot see how to post a new thread.

This is a new thread..Did you check your coil packs.plugs.wires.fuel injector..Also is your CEL on

yep plugs could be fouled from coolant

Ok, back to the beginning.
Before replacing the head gasket, I poured a bottle of Bars Leaks head gasket repair into the radiator, 33oz. I could not keep the car running long enough per directions. The coolant was disappearing as fast as I filled it.
I then started the tear down and when I got to the head gasket, there was about 1/2" of material missing between #4 and #6. I put this all together and started the car. It had a very rough idle. I then went through the troubleshooting process of checking the coil pack, injectors, replaced PCV, plugs wires, used noid light on injector, MAP, MAF, Idle control needle, EGR, found no vaccuum leaks.
I assumed it was either a warped head or valve issue. I installed a new head, gasket, and bolts yesterday. It started great and no misfire until a minute or so later. It started sounding slightly random, then became very steady on the misfire.
When the head was off, I inspected the cylinder and appears fine. The old head has very black exhaust valve on #4, but the other 2 are white.
The other issue that started right after replacing the head gasket was really low oil pressure. It does not register over 40.
When I accelerate, the misfire disappears and while driving, I do not notice any power loss or misfire at all, until it drops back to an idle.
I had this at the dealer prior to swapping out the head for diagnostics, and they informed me that #4 was at 90 on a compression check.
What am I overlooking?

Did you coat your headbolts with thread sealer? They do go into the water jacket.

Your oil may be contanimated with coolant, thus the low oil pressure. Have you done an oil change since the last time you pulled the heads?

The bolts came with sealant pre-applied, and I drained and flushed the oil.

I replaced the oil filter also.

I am not sure if it is normal or not, but I am getting quite a bit of water from the tail pipes when running. A steady build up and dripping. I do not smell any oil there, or sweet coolant smell either, just water.

Hmmm, how are the lower intake gaskets? I have had something similar to what your experiencing. Misfire, eating coolant, etc. It pretty much went away the last time I swapped the heads and applied thread sealer to the headbolts. Along with some kicking and screaming at it.