'98 Bonneville cylinder misfire

[troxartes]

The computer scanner showed the code for #6 cylinder misfire. The car sounds great up until 4000 RPM, at which time it starts to miss badly. It won't go past 4000 RPM and the boost gauge stops at 0. I changed all the spark plugs, and the problem persisted. I changed the 3-6 coil, problem still there. I changed out the ICM, the problem is still there. I've made sure the 6 wire is nowhere near the O2 wire. I've had a couple of guys tell me about coolant leaks from faulty LIM gaskets, but it's the opinion of myself and my father and brother, both mechanics, after observation, that the LIM gaskets are not the issue. My brother seems to think it has something to do with the fuel injection system. My father thinks it might be an issue involving the computer itself.
Also, we tested the 3 and 6 wire to see if that was the problem, but it proved not to be. Using a timing light, BOTH the 3 and the 6 cylinders showed misfiring, with the 6 barely firing on idle.

Any help will be appreciated big time....I need to go back to school in a few days and I need this problem fixed!

[auto trainy]

Try changing the wires with new Delco wires.