I know this is a truck forum but a 4.6L is the same.
On my 99 Crown Vic P71 4.6L I took a 1000 mile trip. On the way back I got awful gas mileage. I filled up at a Fast Strip station in Arizona I have never got bad gas there before but have heard a few stories of bad gas there over the last year. Well I got gas just before the tanker dropped a load. My mileage went from normal 17.9-18.2 mpg to 15.95 mpg. First thought was bad gas. So next fill up was at Union 76 & a can of Seafoam. NOTE (we made this same trip every month or so.) Well just before the we made the second fill up 180 miles later the CEL came on. I read it, a PO302 but mileage was improved a little below normal. So filled it up again with Union 76. drove home 103 miles home, looked like everything was OK on Thursday. Today Sunday 150 miles on fuel I get another PO302 code.
I put in new Autolite plugs, & wires, or boots about 10,000 miles ago. I have had a lean bank codes on the same side & it turned out to be an exhaust leak at the manifold. The top bolt likes to back out.
Where should I look for this random PO302 problem???? Note: normally if I get a misfire I feel it,but not with this condition.
Tomorrow I was going to change fuel filter it is over due, last changed about 25,000 miles ago & check the manifold bolts.
Sorry about the long post would appreciate any ideas or help.

 

That code is: "cylinder #2 misfire" which I'm assuming you already know. If its a persistent problem even after changing the plug, boot and COP then look to the wiring harness connector into the COP. Those have been known to lose contact due a broken locking tab and cause your sort of issue.

 

Thanks for your input.

Last night in the middle of the night the thought of a bad connection or a coil going bad came to me. So far it has come on twice in about 400 miles. But the last time I lost a coil I felt the miss fire. Last night I took it out & put my foot into it ran it WOT through the gears no miss felt no CEL. So I'll check the harness. Checked the connection it was solid so I put some Di-electric grease on the connector, so we will see. Thanks

 

Code PO302 is still haunting me. I changed the plug, new PCV valve. I'm running AP104 Autolites. Which are a platinum plug. It is a direct crossover from the OEM Motorcraft. Motorcraft's are hard to find. Anyway started it up after plug change & still showing a misfire #2 cylinder. So I decided to swap #2 & #3 coils. So far the jury is still out.
Any ideas from here. I checked connections on coils & injectors.

 

If P0302 continues coming up you know there's a problem with that circuit somewhere along its path back to the ECM.

If P0303 comes up you'll know its in the COP or its boot.

 

The PO302 keeps coming it it appears. It hasn't thrown the CEL but my reader keeps detecting it. The funny thing is I can't feel a miss so it is something that appears to happen even at idle but I can't feel even a slight miss. Every miss before has been a noticeable miss.
So where do I start? It sounds like it could be in the ECM? It happened all of a sudden. It ran great up to the point of the CEL.
Thanks for your response. I'm about to give up on this car. I bought it cheap $450 & put a few thousand in it, but it seems like it wants to start nickel & dime me to death. I have put 30K on it in less than a year & a half. Once my friends estate comes out of probate I have spoken for his 01 Crown Vic P71. Maybe I'll just take the new tires & stuff off this one & put it on the 01 which has less miles (155,000) & runs much better mainly because it was taken much better care of by the County that owned it than the County that owned mine.

 

On another forum it was suggested to check FI connection & if loose to replace. Well the #2 connector had a broken lock clip. So since I had to order new connector I thought I would use a plastic tie to hold it on tight. Well it appears to of stop throwing codes. So I will drive it and see if the CEL comes on again. If this fixes it I might plastic tie them all.
Thanks for the help so far.

 

Smart move. Those little plastic latches get brittle on about all our connectors > 10 years old and it only takes a momentary loss of connection for the ECU to detect it / set a code. And they charge insane prices for them.


Sounds like your new connector will solve the problem.

 

Unfortunately it didn't fix it as I had hoped. So I checked the air filter & it was dirty 30K on it & high desert dust & dirt.
Then I added 8 ozs. of 91% rubbing alcohol to the gas tank. Yesterday we drove 170 miles on the road & in town & No CEL. So maybe that was it. I do know my 99 Crown Vic P71 will set off the CEL without much effort. A slightly loose exh. manifold to pipe bolt caused a lean bank code & O2 sensor code. The bolt only would turn about a turn.
Oh the gas mileage was back up to 22 mpg.

 

Wrong thread.