BlkGTjax

I am completely stumped. The car is a 2003 GT with about 106000 miles on it. It has a p0304 code on it. I checked the coil packs (which were replaced about 1-2K miles ago) and replaced all 8 plugs with bosch platinums gapped at .054. I've checked the fuel injectors even though I replaced them about 6K miles ago. Everything checked out good. I didn't really have time to mess with it because of work and school, so I took it to the shop.

The shop said that the intake manifold was cracked and that cylinder #4 coil pack was bad. I decided to do it myself for less than 300 vs paying them 1000. I got everything back together, and cleared all codes. It drove fine for about 50 miles, and then I got a code for cylinder 4 again. I took propane and checked for vacuum leaks, didn't check fuel pressure before I changed the fuel filter, but afterwards it was at 45psi. Hooked up a vacuum gauge, and it stayed steady at 20. Switched the coil pack from 4 onto cyl 5, cleared codes and drove it around the block. Comes up with p0304 again.

I've replaced the intake manifold gaskets before on a couple different cars, and I was very thorough in cleaning and torquing everything, so I doubt there's a problem there. I pulled the spark plug on #4 and it has an oily residue on it. I'm guessing it's from fuel not being ignited, but that may be because I don't want it to be worn valve guides or piston rings.

The car isn't smoking, and cylinder 4 seems to be completely dead. I plan on doing a compression test tomorrow. Does anyone have any suggestions? I read on another mustang forum that a bad fuel rail sensor will cause cyl 4 to misfire, but that doesn't make any sense to me. I'm also guessing that a bad IAC wouldn't cause it to misfire on the highway nor on just one cyl consistenly.

Any advice would be much appreciated. This engine is driving me crazy right now.

cliffyk

Here is a description of how the misfire detection monitor works. A damaged or dirty crankshaft position sensor (CKP), or damaged crank position wheel, could make a single cylinder be reported as misfiring when in fact it is not.

Here's the RnR for the CKP...

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BTW--is that "jax" as in JAXonville, FL?

BlkGTjax

Didn't get to the compression test the other day, i got called in to work. Plan on doing it tomorrow hopefully. I went ahead and replaced the ckp sensor today since it was only $15 and took about 10 min to replace. Kept the battery disconnected for about 15min before starting the car. Also ran the code reader prior to startup and it didn't show any codes.

I guess I'll do the compression test and go from there.

The name is from jacksonville,FL I lived there for about 4 years when I was in the navy, I've since moved to Kansas. I've been to Saint Augustine before it's a pretty nice place. I definitely miss florida especially during the winter months.