This problem has bugged me for several days already and still the check engine light stays on. The vehicle is a 1999 Cadillac Escalade 5.7 with code P0306. P0306 is a cylinder #6 misfire code. This is what I have done so far: New spark plugs, new plug wires, new cap and rotor, new fuel injector, new air and fuel filter. The compression test shows 150 psi which is very good still, especially for a vehicle with 185 k miles. I have cleaned the air mass sensor, the throttle body, and the connector points for all other sensors as well. Thinking that I may have installed faulty new plugs or wires, I then tested them and moved them around, no difference. Any suggestions anyone? Thanks

I think the 5.7 has individual ignition coils for each cylinder. Switch the ignition coil for cylinder 6 with another cylinder and see if the misfire follows the coil. If the misfire follows the coil, replace the coil.

When you pulled the plug, did it look any different from the other plugs? I've seen twice now a broken valve spring cause misfire, and still pass every test we threw at it until we removed the valve cover and actually looked at it.

Great idea, but I forgot to mention that this engine has only one ignition coil. Well what else??? Thank you.

Here'* what can cause a misfire, most of them you checked.

Bad coil, but you have one so not likely.
Bad dist cap, and or rotor, you swapped them
Bad plug wire, but you swapped them
Bad plug, you tried new ones.
Bad injector, you swapped them.
Bad injector plug, need to test that.
Bad valve spring, need to check that
Damage, such as chipped piston, need a bore scope to check that.

When I did the compression test, I did it whith the valve cover off to check the lift of the rockers and inspecting the springs. They look fine but I do not know if they could be weak. The engine runs fine in higher rpms but idles a little rough. Thank you

Look around for vacuum leaks, like the EGR tube. That can cause problems as well. A bad spring of chipped piston tends to show up more at higher RPMs.

I have checked for vacuum leaks everywhere and cleaned and checked the egr valve. I'm not sure if an o2 sensor could cause this. I guess I'll check the o2. I do not think a bad o2 would affect only one cylinder but I would'nt be surprised. Thanks again...Mike

he should have vortec 350 which has an injector spider setup, it does not have indiviudual injectors to replace. it does have a kit you can buy to upgrade to individual injectors because the setup is problematic. the kits are expensive though so you want to be sure you know thats it before you lay out the cash.
http://www.amazon.com/Delphi-FJ10566...2622365&sr=8-1