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i have been having a problem with my 06 f250 5.4 running lean (p0174). took it to the dealer yesterday and they did a smoke test, checked fuel injectors, fuel pressure, and hooked a laptop to it and did a road test. everything checked out good. at wot it hesitates, kinda jerks, and bucks, but normal highway driving it does fine. the idling is pretty good, but fluctuates a little when shifting from forward to reverse. they said at wot cylinder number 5 was dropping out (whatever that means). the mechanic told me he would start by changing the plugs. the truck has 75000 miles on it, with the original plugs. does anyone think it could be the plugs? or could it be something else. i dont think the tested the coils, they didnt say anything about them. i would appreciate any help i can get thanks.
A catalytic converter problem is very possible. If you have a partial clogged cat, you won't be able to flow enough exhaust at high engine speed, but at normal engine speed your engine runs fine.
I believe that catalytic converters are covered under a 8 year / 80K emissions warranty... Considering that your F250 has 75K miles, you need to get the dealership to fix them asap.
it could possibly be the cats failing, because i used to hear a real bad rattling noise from the exhaust if i was coasting around a curve and then when i would get back on the gas a little it would rattle bad. i always just assumed it was just a loose heat shield or something. maybe the rattle was loose media moving around or something.
i guess i need to have the shop check them, but they will probably try their best to get around replacing them under the 8 year/ 80000 mile warranty.