my '03 Mazda6 (Duratec V6) set some Random Misfire codes over the last few weeks, and may have also set a Lean Bank code (I didn’t write them down and am too old to remember). So I put a set of OE Motorcraft plugs in it, which required removal of the upper intake due to the packaging of the COP ignition. Now, it is setting P0303 Misfire Cyl 3 and P0171 Lean Bank 1 -- but not the Random Misfire. I am confident that I didn't screw up the intake gaskets (I actually used new ones!), so I'm wondering if I've got a weak injector or a weak coil on cyl 3. I can pull the intake pretty quickly to check gasket integrity, but will do the spray test first to see if idle quality changes before I do that.
Does this combo of DTCs make you look in one particular direction? Especially knowing the recent service? Do these cars have a history of killing coils?
One last thing: I got some misinformation and gapped the plugs at 0.044". Since then, I have read that they should be at 0.052". I do not suspect this because all six are gapped the same, but I will probably pull the intake and set them all to the proper gap because that's how I am.
