So I went to a car show in Daytona today and when I got back in to go home my 2000 F-150 5.4 seemed to be acting a little funny.

First off, when climbing a little lip from the dirt parking lot to the asphalt road (I was just easing up it) it almost felt like the truck was going to stall out. Then we get down the road a bit and the "Check Engine" light comes on. Truck seems to be driving fine though.

Let it sit while eating, and drive home. On the way I was accelerating a little and noticed a really hard shift going into 3rd gear.

So I get home and decide to take it up to Advance Auto Parts and try to get some codes thrown at me. I got two.

P0171-
System Too Lean
(Bank 1)
P0174-
System Too Lean
(Bank 2)

So I brought it home and checked all vacuum lines, sprayed out the MAF with electrical contact cleaner, and just did a general overview. Everything checked out and all the MAF did was up my idle by about 100RPM's.

My question is, Could this be an O2 sensor problem? Or would that result in the fuel/air mixture being too rich? I noticed my exhaust smells like nothing, no gassy smell at all. Any other insight to the hopefully not so drastic problem? Thanks in Advance guys, haven't been on in a while cause it's been running so good!

(Check Engine Light still on)

 

I was having that same issue with my wifes car. The CEL was on and the codes read system lean on both banks, which points to the O2 sensors. The car would lope in the morning like it wanted to die out until it warmed up. I replaced the O2 sensors to no avail. I than tried to clean the MAF and the car started acting all stupid doing the lope thing that it did in the morning all the time, and when you would accelerate it would act like it was gonna die. I replaced the MAF and everythings back to normal. No lope, no CEL, no stumble and increased gas mileage. My F150 has only thrown a CEL one time and that ended up being the gas cap, currently have 208,000 miles on it.

 

Nope, not an O2 sensor problem. Recheck that PCV tube one more time. Especially the rubber elbows where the hard plastic portions join together.

 

O2 sensors do NOT cause lean codes, especially on both banks at the same time. This is almost always a vacuum leak, sometimes (but rarely) a flaky MAF sensor.

A high idle is another sign of a vacuum leak....

Steve

 

So over the past few days, maybe even a week or longer I noticed a whizzing, whining noise (Almost like squeaky belts) coming from the engine compartment, I assumed it was either the belts/pulleys or the alternator.

I pull off the PCV hose and notice the sound stops, Idle stays the same. I looked over it and don't see anything ridiculous, no large cracks. But I ordered another tube anyway from the stealership. My dad accidentally drove with the PCV tube still off and said it drove exactly the same. I'm assuming there is a pretty major leak somewhere now.

How long would this have to occur in order for the computer to start throwing codes? Down shifts seem to put me back in my seat less and idle is weird lately. But that whizzing whining noise has been going on for a little while...

Thanks in Advance...

 

Replaced the PCV valve end and it stopped the buzzing, but I'm resetting the computer to see if it did anything.

Also, when I take the brake booster line off, the whole truck stutters like it's going to die, and it bogs high and low. Should that be happening if there isn't another leak?

 

Pulling the booster line created a massive vacuum leak.

What were you expecting?

Steve

 

Well I remember when sea-foaming it not bogging so much. I guess I must have had someone keeping the revs up a little while doing it.

But Anyywayy... Turns out the MAF had a little black piece of plastic wrapped around one of the little wire sensors. very carefully took it off and blasted it with some electrical contact cleaner.

Seems to be all better, not throwing codes anymore...