Ok here goes. I had a CEL for misfire under 1000rpms with no specific cylinder misfire code. The car was idling rough but drove fine with the exception of a hicup here and there while accelerating. Decided I would Easter egg the COPs by buying one new one and replacing till the CEL went away. On my way back from the parts shop CEL started flashing so I imediatly turned around hoping to get it scanned and find a specific misfire code. Got code for #8 Misfire so I went home replaced it and test drove it (BTW replaced the drivers side rear COP #8 so you guys know i got the right one) and it ran smooth as silk and idled great. Even seemed to feel more spunky. Shut it off and went inside. BTW I had the infamous water in the COP galley problem. After reading about this problem and where the water comes from I decided to go back out and look at Cylinders 5, 6, and 7 since they were all exposed to water. When I started it up after examining all of them the friking CEL came on again. Ran to autozone and now its throwing Misfire #3. Grabbed another new COP and went home to replace it (3rd COP from the front of engine on passenger side). Cleared the code and fired it up. Still random misfires at low RPM and CEL is on again saying same thing Misfire #3. That's when I noticed a slight whistle sound emanating from what seems to be the center of the upper intake plenum. It only does it around 700rpm-just a hare over 1000rpm. My thoughts are a vacuum leak from the between the upper plenum (plastic) and lower intake (aluminum) manifold. Has anyone ever heard of such a thing on the LS8? I bought what was SUPPOSED to be an upper and lower intake manifold gasket set online but when it came it was only the metal gaskets for the lower intake manifold where it mates to the cyl heads. Any way I am screwed as no parts store local has the gasket for the upper plenum. Any part #s and ideas would be much appreciated.
Oh and yes there is oil in 3 of my COP well i used a syringe to suck it out then cleaned the walls thorough before reinstalling my new COPs. I intend on replacing the valve cover gaskets ASAP if I can find some lol. I ordered some felpros on the internet but got V6 set so i cant for the life of me find the part # for the v8 set.
Ford wants $90 per side for them and they have to order them. sigh.....
Any way now that I wrote a novel here lol any suggestions are welcome as well as part numbers. I have been reading forums till my eyes are bleeding and really could use help.