Missing above 4000 rpm——help please

[mykonos]

I ran through and read posts I could on misfires, but couldn’t find anything. I’ve got a 2008 gt with 48,000 miles. The car runs great at low rpms, but when you get on it then it’ll miss above 4000 rpms. Throws misfire codes for both random and cylinder 6. I have replaced fuel filter, plugs, coil packs and injectors. Still is doing it…. Anyone have this before?
The car also smells like urine after so could it all be the cats being bad? It has had a catylitic insufficiency code that I have cleared. Could clogged cats cause the misfires? Or could this be a timing issue and need new cam phasers? I am at a loss.

thank you guys/gals for the help. It’s appreciated.

 

[mykonos]

K....i had a similar prob with my '08 Bullitt....the IMRC wouldn't open sometimes.....the controller is mounted on the back of the engine, not far from the firewall. Theres an arm that connects to it on top. From drivers side, pull the arm toward u, to see if it moves freely. I used a piece of #14 wire....tied it to the top arm
of the contrller, then pulled it as far as it would go....and tied it off to whatever is handy. (I wrapped it around the a/c freon suction stub on the suction accumulator (with black cap on it.). Go for a drive...see if it runs normally. I left mine connected for a couple of weeks....then removed the wire. That was about 2 months ago. Still running as it should. No probs.