I have a bad misfire on a 3.0. I've changed the coil and plug twice, cleared the code and there is no change in the rough idling and obvious reduced drivability and my gas mileage is way down and I think it's made my cats go bad p0420? I assume that gas is being dumped which in turn could be giving me the p0420 but why would I have a misfire if I change plug/coil twice and it has a spark? Could It be the fuel injector, values or what? I'm kind of lost at this point.

 

Year and model, and where was the #5 you replaced ?

 

2000 stype 3.0 and i intially replaced them all then #5 one more time when I got the 305 code

 

Well #5 on yours is middle cylinder drivers side, is this the 1 you changed. If so i would swap coils from adjecent cylinder to see if follows, but the connectors after that age break easy and then dont stay snapped onto the coil coming loose, i usually have to rig up tie straps to hold the connectors on. Barring all the previous you may have an injector leaking, but not common, but you can swap injectors too and see if the faults moves with them as well, at least you have a constant msifire, but yes you need to fix before the cats toast. If not already

 

yeah thats the one I changed but i didn't swap it with another coil to see if it followed. If it still misfires on #5 with the coils switched is it safe to assume that is either wiring or fuel injector problem? where are the injectors located?

 

i stuck a nail in the coil to see if it was sparking and it had a spark

 

Brutal may disagree, but I believe you have a faulty injector.. This very same problem happened in my Audi and for months it sounded like it had a lumpy cam and I could never figure out why.. Well turns out that my one of my aftermarket 870cc injectors had gone bad.. I was very pissed because they were $120 each, but I got the manufacture to send me a new one for free.. I would have toasted my cats as well, but my car didn't have any.. lol

 

No str, I agree, the injectors are the next loggical choise to look at. Theyre under the intake, and on their own assembly. You can remove the whole lower injection assemly, injectors and all. But if memory service me, the rails and injectors are installed at an angle very hard to r n r. Thats why we get them as an assembly, with new injecotrs. Someone else is gonna have to offer more aftermarket info, than I have at home right now

 

Great info guys I'll check into that asap and hopefully I'll get my baby back into tip-top shape. I'll let you know how it turns out. Thanks