Are they necessary? I now have a multiple cyl missfire issue (P0300) and i never did reinstall those heat shields after the heads and cam swap, just wondering if they can cause spark plug issues if not installed. As far as the missfire issue goes, i thought it was my o2 sensors so i disconnected the harness so it could run open loop and the missfire is nowhere near as bad but still very noticeable, what do you guys think? I hate that damn code it could be anything, i could shoot a video if needed.

Update: Missfire seems to decrease at WOT but drives like crap below 3000rpm.

 

Are the boots melted at all? I didn't put mine on when I put my MSD wires on and I have no problems. What cylinders are misfiring? Have you tried to move the coil packs around to see if the problems follow the coils?

 

Check your coolant temp sensor.

 

I got owned by that sensor

I forgot to check this thread, i ended up changing all the plugs and wires, and o2 sensors before realizing that the coolant temp sensor somehow came off Oh well it needed a good tune up anyway missfire is gone.