This is random going down the interstate, at first i thought plugs and boots but I replaced them 2 years ago with no troubles. Could this be a plugged cat. It has done this at idle.

 

Mine had the same problem, i changed spark plugs, coil, clean injectors, fuel filter and the problem haven't gone, change the catalytic converter and everything come to normality

 

I am now getting p0304 and p0307. I am thinking the same. Is there a sure fire way to find out.

 

i had visited the muffler store and they had to remove the cats..

 

Well first I am going to try the fuel filter. It has the most in common with 3,4,5 & 7 cyls.

 

Now I'm thinking its not the fuel filter. It goes into fault mostly when decelerating like going down hill or at an idle. Any thoughts???? Vacuum leak????

 

Two of the offending cyl 3,4 ??

 

New Motorcraft platinum plugs,boots air filter and fuel filter. 200 mile no more check engine light.

 

So what was it?
The plugs?
The boots?
The air filter?
Or the fuel filter?

 

I think there was some restriction in the fuel filter but it faulted going downhill, makes no sense but it could be. It appears I am getting better gas mileage so maybe those iridium autolites aren't to good they were a little black on one side maybe fouling occasionally which could have been the problem. The boots were swollen a little and not from oil or water so maybe they could have had something to do with it. The air filter was dirty but I doubt it was the problem. There ya go that's what I think. Oh I did spray the mass air sensor down with cleaner but I don't think it did anything as it was clean.

 

I went 2 months and its back and not everyday seem every couple weeks it will do it several times during my 40 mile commute. I'd like to figure it out. 300,304,307 now.

 

my daughters 2005 4.6 motor had a couple random miss fires.. I put several coils on over a 2 year period... Seemed to work temporary... no long term....... Finally I bought new injectors and installed... I had CLEANED the original, but still had problems.

 

NOTE: Melted cats are the END results of misfires not the ORIGINAL cause.
Misfires allow unburnt gas to burn in the cats raising their temperature to over 900 degrees.
They are not designed to run at those temperatures. Only just hot enough to treat the exhaust gas at about 600 degrees.
Letting multiple misfires go too long becomes very expensive..
Good luck.

 

Chasing them down can be too.