Hey, I bought a 03 f150 5.4 a while back (120xxx miles) about 6 months ago I got a check from engine light for cylinder 2 misfire. Pulled the plug out and coolant was on the plug. Took it to a mechanic and they told me I needed a new intake manifold. They called me back after they had started working on it, and told me I needed a new timing kit put on and valve cover gaskets. I got the truck with new valve cover gaskets, I take manifold, and timing set. ( note that the problems I’m about to describe DID NOT occur before my initial misfire before I took it to the mechanic). Not even 5 minutes after picking the truck up from the shop, I noticed hard vibration at idle and some power loss. I took it back to the shop, and they said my cat on the passenger side was around 600 degrees and needed to be replaced or cut off. I had the cats cut off at a local muffler shop and replaced with pipe. Needless to say, the issues were still occurring. I took the truck back to the shop, and they told me the aftermarket intake that they put on was basically a dud and that they were going to replace it with a new ford intake. I got the truck back with the new intake on it and the issues are still the same. It’s been about 4 months or so since then, and I have barely driven the truck. The past week, I have replaced the fuel filter, put new plugs in cylinders 1, 2, and 3, and replaced the plug boots for those cylinders ( i did use dielectric grease). I have unplugged and plugged back in each fuel injector and each coil pack 1 by 1 while the engine was running to see if each was functioning properly. When I unplugged the injectors and coils on bank 2 they bogged the engine down far more than when I unplugged and plugged them back in on the passenger side ( it almost seems like bank 1 is running with half power). I have cleaned out the throttle body, visually and audibly checked for vacuum leaks, and unplugged and plugged back in basically every sensor at the top of the engine that pertains to the engine. No check engine lights have came on except for when I unplugged and plugged back in the MAF and IAC. No other codes appear. The exhaust also smells a little like gas. I’ve also noticed that when the engine is cold, it seems to run normal, but when the engine starts to warm up, it starts missing. I am at a loss and don’t know what else to do. Can anyone give some guidance ?

 

I don't know about good guidance, but I would strongly suggest we start with a compression test . That should at least let us know the mechanical parts are working.

Before going any further, let's see what the results of the compression test show.