System Too Lean (Bank 1 & 2)

[Alyusha]

Hey everyone,

1999 Expedition XLT 5.4 4WD

CEL came on tonight and upon checking it came up with P0171 and P0174 which are System Too Lean Bank 1 and System Too Lean Bank 2. I have done some looking around and have come up with several things that could be affecting this.

I am hoping that it is the PCV line because it seems to be an easy and cheapish fix. But like I said, there seems to be at least 4 different things that could be causing this, and I don't know another way to figure it out without replacing each and every part in hopes that it is the part that is causing the codes, and I can't do this.

I seen on another forum that if one code popped up, it could be the O2 sensor, but its unlikely for both to fail at the same time.

So anyways, I am looking for any advice on where to start, or someone who has had the same issues going on and can point me where to look.

Some recent issues that have started, that may or may not be related, but I feel I should disclose...

1. My blower does not seem to blow from the panel vents, its almost as if my heating system is stuck on defrost. When I turn the panel blower on, it blows out on top by the windshield. The vents for the feet work, and the rear works fine.

2. I have noticed that I am not getting as good of gas mileage as I recently did.

3. My gas gauge needle will jump around sometimes. Not from saying 1/4 tank to full tank, but like bobble up and down quickly.. This does not happen all the time, but it defiantly never used to happen!


Thanks for any help.

 

[1955moose]

This a very common problem on all expeditions, especially first and second generation ones. The usual culprits are spark plug/ coil problems. If you read some of the other recent threads, you will see similar problems, and repair solutions. Basicly it's tune up time first, then further diagnosis after that. Please read other owners recommendations, that have done this repair. As far as your heating issue, their are also 2 recent heating issues similar to yours. Again read what they did, it should help you in you diagnosis. Good luck, please post your progress, it helps others like yourself, with future problems.


Sent from my iPhone using Tapatalk

 

[glen r]

I had the same codes a few years ago on my 01. Replaced PCV and all vacuum lines with no affect. Had it smoke tested twice. Second time they found a cracked manifold, apparently cracked when the temp sensor was replaced.

 

[Bedrck47]

I once read that anytime a code comes up that refers to many items and O2 sensors are involved Would be best to check all item and save the O2 sensors for last as many things can cause false O2 readings

Item #1 Vacuum lines could be the problem.

Item #2 could be a need for a tune up Plugs and new boots

Item #3 Possible a bad float sensor I had that on my 01 The pump was good but the float was the cause of false readings

The tank level is a variable resistor and the action of the float changes the readings Sometimes over years of fill ups and low fuel levels the variable resistors get worn and gives false readings

 

[docraymund]

Try taking fuel pressure readings might be a weak fuel pump. Replace the fuel filter. Clean the MAF sensor.

 

[Alyusha]

Thanks for all the info everyone. I did check the PCV elbow and it looks perfect.

I think I am going to try cleaning the MAF sensor first and see what happens. Is this pretty accurate info as far as the 5.4 engines go?

Part 1 -How to Clean the Ford MAF Sensor (Ford 4.2L, 4.6L, 5.4L)

Thanks.

 

[Bedrck47]

read this also

http://www.expeditionforum.com/191356-post1.html

 

[Alyusha]

Maybe I should have said this in the first place, but my alternator did just die and I had a garage replace it the day before CEL came on. Is there anything in in the process of replacing the alternator that may have been unplugged or removed that may be related to this?

 

[Bedrck47]

Shouldn't be anything that needed to be unplugged to change out the alternator. But then its hard to tell what or how other people do things

 

[glen r]

They would have been working around the front of the intake.