I have a 99 F150 4x4 4.6L that is having some serious issues. My fuel mileage sucks and it has a real bad miss. Yes I get a CEL no I have not had the codes ran. I changed plugs and one plug (passenger side firewall ) was covered in oil from top to bottom. Once the plugs were changed all was fine for 4 days. Now all problems are back. Misses, shudders, sucks fuel, stinks and smokes on start (whitish smoke) The miss and CEL is real bad at 3000 rpms if I backout it gets better but not great. Am I screwed or do I just have a leak ?

 

Take a look at the plug again. Is it oil or old and equally greasy antifreeze? F150s have a problem with hose leaking antifreeze over the back plug on the passenger side and causing problems.

 

The plug was very black could not tell if was anti-freeze or oil. Did not really smell like either. Would the old anti-freeze eventually turn black if sitting a while on a non-sparking plug like that ?