Hello everybody,

I got a 2001 f 150 with a 4.2L V6 with 32,574 miles on the motor. it seem to misfire when you put a load on the motor , it idles great. I replaced the plugs and wires and it didn't solve the problem it seems to get worst when it rainning or lots of moisture outside it hesitate a lot more. can anybody help.I was thinking of changing the coil pack..

 

These are kind of the symptoms that my 98 e150 with the 4.2 L is doing currently. Does it misfire at all rpm's..or just at a certain rpm? My van is only misfiring at low rpm. The dealer says the egr ports need to be cleaned.

 

hey guys, i've got a 4.2 in my '99 f150 w/ a five speed and alas, only a 4x2...but anyway, i've also had that problem with the misfiring, i'd say that it's not a problem w/ the coils b/c if it were, u wouldn't idle good like everyone says theirs will, as does mine. The egr ports sounds like a very possible problem, but would that happen to throw an engine code? i have no idea, but i'd assume that it would mess w/ the exhaust gasses and throw off the O2 sensors, but i'm not for sure, that's more wishful thinking then anything....but the way it was described to me was that for some reason, these engines (and the 4.6) are prone to carbon build up on the cylinder crowns. when this happens, the carbon heats up and pre-ignites the gases in the camber, thus causing misfire...this seems to make sence in my case b/c it never misses when the engine is cold, but i've never really noticed a difference when it rain or there's high humidity in the air, i'm going to run a can of seafoam thru it next time i fill up and see if it breaks up any of that carbon

...also, does anyone have firing problems when you run E10 gas in ur engine? i kno mine does and i think may be a contributing factor to this carbon build up problem

 

Clogged egr ports caused my 4.2L to through a code. I believe it was p406.
I had them cleaned out and the van is running very good now. It was having misfiring issues at low rpm's. The carbon build-up definetely thru the code. You could try seafoam, but on a engine that old your probably going to have to clean them out with a brush.

 

that's still a very real possibility, but my truck isn't throwing any codes...i'm not going to rule out the egr ports yet but i'm gonna start w/ the easiest fix first...hopefully a 7 dollar can of seafoam can keep me from tearing into this engine, i kno how to do it, i just hate working on newer pickups...i'll let u all kno how it turns out!

 

my truck is missing also (2002 4.2 4x4) threw a code bad crankshaft position sensor...missed at low rpm and high reduced power bad gas mileage n all, changed the sensor but when i took the old one off there was alot of metal shavings and the sensor war all f'ed up on the inside? put the new one on, helped a little bit but at high rpm has reduced power then missfires? buddy thats a ford mechanic says its probobly the sensors syncronyser inside of the timing cover...hope that helps