The same old coil issue, I think?

I have a 2004 v6 Lincoln LS with 54k. I got the error code P0303 which indicated misfiring on cylinder 3. Having read many of the posts on this board, my immediate assumption was that oil leaked into coil 3. But I have a couple of questions.

On the report Autozone gave me, it says that this problem could also be caused by fuel injector or fuel pressure issues. As it turns out, I just replaced the fuel filter 4 weeks ago. The gas that came out of the filter was nasty brown. Could the gas prior to me changing the filter have caused this problem by clogging the fuel injector? Could something I did when I changed the filter caused this problem? Let your thoughts. How do I check for this?

Also, my guess is that coil 3 is on the left hand side (looking at the engine) under the manifold. Alot of people have commented on changing the coils and cover on a v8. Any comments on the difficulty of taking off the manifold and doing this on a v6.

Thanks in advance!

The printout from Autozone is correct, it could also be due to an injector/fuel issue. And you are correct, #3 is under the intake near the firewall. It's not an easy one to get to, but you'd have to get the intake off to get to the fuel injector as well. The first time I took the intake off of a V6 took me a bit over an hour being cautious. This was on a 2002 with the mechanical throttle body. I believe your 2004 has the electronic throttle body (throttle by wire) so that will reduce some of the hardware. The EVR is probably still mounted on the backside of the intake though, and that's not an easy one to get to. I ended up loosening up everything so I could get the intake a bit forward as that was the only way I could see to get the connections loose from the EVR without breaking something.

If you have a scan tool with datastream capabilities, and are able to duplicate the misfire (power braking the car, etc.) under load conditions, you could monitor the bank 1 air/fuel ratio. If immediately after a misfire the ratio goes lean, then you probably have a fuel issue. If it goes rich, then you probably have an ignition system (coil misfire) issue. If your datastream doesn't offer the Rich/Lean discrete, you can monitor the Bank 1, Sensor 1 (B1S1) oxygen sensor voltage for rich/lean as well.

If you end up pulling the intake to fix the misfire, consider replacing the plugs while you're there as well as the PCV elbow which is below the lower intake manifold and not much fun to get to. I was fortunate that the dealer I went to was able to find a similar elbow that worked from a different application rather than expecting me to order the more expensive PCV tubing assembly that shows up in the books. I think I still have the Motorcraft part number of what they sold me if you're interested.

-Rod