My 98 F150 4.2 threw a check engine light today. I have a code reader that shows PO171 & PO174. In the Chilton manual it only shows:

PO171 System too lean (Bank 1)
PO174 System too lean (Bank 2)

Starting with the simplest solution and something that was a little overdue, I replaced the fuel filter and reset the computer. It drove great for about 4 or 5 miles, then at a red light I felt a really light rough idle and the light came on again. I plugged the reader in once again and the same codes came up.

So my question is, has anyone had these codes come up and what ended up being the problem? I don't want to replace the fuel pump, fuel pressure regulator, fuel injectors etc... trying to isolate the problem. If anyone can advise me I'd appreciate it.

 

hey there
a $100 dollar bill says its a vacum leak on the intake look at the back of intake there will be a rubber elbow near the fire wall or in that area it has cracked or came off . check all vacum lines very good

 

That isn't even a bet..it would be like stealing candy from a baby.

I'd give it better than an 80% chance on being the cause.

Steve

 

ok steve you got me

remember my last post about this same thing?
do you know how much of a pain in thea$$ it was to fix?

 

Follow the PCV tube from the rear of the passenger's side valve cover to the underside of the intake manifold, near the throttle body. You'll probably find it rotted through there somewhere.