I have a 2005 chevy cobalt it wont start ive
changed the fule filter, fule pump relay, fule
injectors, spark plugs, ignition control
module and the o2 sensor. Hooked it up to a
diagnostics reader and all it said was that 4
cylinder is misfiring
Is the fuel pump operating? Do you have fuel pressure?
Yes I have fuel pressure
Likely a sensor or a bad electrical connection somewhere but that's just a guess at this point. Before spending more money on random parts and hoping for a miracle I'd spend a few dollars on some professional diagnostics.
I had my mechanic friend do diagnostics test on it and he looked at it and said its the coil pack
That sounds promising. Did he scold you for changing all those parts without finding the problem first?
No everything did need to be changed but the ignition control module
Oh good. I hate seeing people pour hundreds of dollars into an old car "searching" for a fix to a problem before they get around to actually doing some diagnostics. Hopefully you'll be up and running soon.