I have a 2001 F-150 4.2l v6 single cab stepside 4x4. the truck has 172k on it. ive been having a problem with it hesitating off the line and also feels like its misfiring when at cruising speed running around 2200rpm. check engine light comes on a keeps saying different cylinder misfires. also sometime says too lean bank 1 or 2. ran all kinds of injector cleaners on it. had the injectors prfessionaly cleaned. complete tune up done twice. new cats on it 30k ago. even put a new coil pack on it. it also does it worse when its cold. very raely it will also hardly even drive until it has completely warmed up. it will drive like a couple cylinders are not firing at all. when this happens, it has no power and it i try to gun it, it will knock under the hood like crazy. other days it will drive like its brand new. most of the time it will just "skip beats" while cruising or while getting up to speed. when i gun it on these days, its got all the power i should have. any suggestions?

 

As I am the only guy here that fesses up having the 4.2, I'll give it a go. Obviously we need to go after the codes. The PO171 and PO174 is the easiest but don't seriously think its your entire problem. When I was getting the codes my truck still ran perfectly. It was an intake leak in that big black plastic plenum chanber that sits on top of the engine. While apart I observed two runners to each cylinder. Long ones and short ones. There is an actuator crammed between the engine and firewall near where the heater hoses go thru the firewall. Don't know what it is called but it opens a plate in one set of runners. I think its sort of like secondaries on a 4 barrel carb. Wish I new more, perhaps one of the tune guys will jump in and help out. There is a post telling step by step how to change the seals that repaired my truck. I don't remember who put it up but it was good. About 6 months ago. The key is to cut the insulation just below the heater hoses, its real narrow there and that allows the removal of the insulation for access to the bolts. Its tight but do-able.