P0171 & P0174 OXYGEN SENSORS SYSTEM TOO LEAN INQUIRY

[StibbyWonder]

Hi guys! I just registered here in the Ford Expedition forums as I go deeper in searching to resolve my problem with my Ford Expedition 2003 XLT model and I am desperate to get knowledge and answers from you respected professionals with Ford.

The history of the car when I repaired it, is firstly, I repair the PCV vacuum leak and then replaced the 8 pcs newly motorcraft spark plugs and thoroughly cleaned all the ignition coils before putting it all back together. While I conducted a drive test with the car, and reached roughly 50-70 kms on the road, the service engine light went on. I used my scanner and conduct the scanning and live results. It came out to be P0171 and P0174 which the codes said system too lean bank 1 and bank 2. When I searched about it mostly of the codes pointing me out for the oxygen sensors. Kindly see attached image below for reference of the live results.


My question is:

1.) is the live results are fine? I don't have any idea in which percentage those should be or shouldn't.

2.) Are the oxygen sensors for upstream and downstream are the same both for bank 1 and bank 2? I am planning to replace it all or maybe just cleaned it first. I hope you can help me out and hopefully resolve this one.

I just clear the code and continue with my driving and it happened that the service engine light didn't come back but after a week of not using the car, then I started it and have it reached the optimum motor temperature, then the engine light went back on again. I am confused, is my oxygen sensor not working or should I just clean it first?

Thank you!

 

[99WhiteC5Coupe]

This MAY help: https://www.expeditionforum.com/threads/p0171-p0174.52588/

And

1998 Ford Expedition P0171 code and P0174 pending

I've got this code and trying to diagnose what's the issue. Upon inspection I found this line/hose (image attached) very worn out. Any ideas if this is causing the codes (P0171 and pending P0174)? What part is this? Thanks for input.

www.expeditionforum.com

 

[SafariGoneWrong]

Your Long Term Fuel Trims for both cylinder banks are saying the PCM is adding about 30% more fuel than the engineers mapped for the operating conditions you're doing. That points to a vacuum leak @99WhiteC5Coupe linked to and it seems to be a common failure line (I replaced mine preemptively earlier in the year). I wouldn't worry about doing anything with the O2 sensors as both cylinder banks are affected. Regarding what Long Term Fuel Trim percentages are fine, it depends... but let's say anything from 0 +/- 10% is good.

 

[Hamfisted]

You have a big vacuum leak. I would recommend doing a smoke test of the intake system to find the leaks. For your long and short term fuel trims, you want a combined fuel trim of not more than +10% . Clean your mass airflow sensor as well. You may even need to replace it, depending on it's condition. What is your MAF reading at idle now ?

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[StibbyWonder]

Wow this forum is awesome! Thank you all guys for your inputs and will reply to it once I follow all your recommendations.

Also I forgot to include in my inquiry is that there is a "hissing" sound in the brake pedals. I'll try to take a photo of it where the hissing noise came from. When I go to the engine bay I didn't hear a single hiss noise. Is it possible that will be the culprit?

Thank you!

 

[Hamfisted]

Yes, the brake booster can be a big source of vacuum leak if it's bad. If you hear hissing, try and determine if it's the booster's check valve there where the vacuum hose attaches. That is easily replaced. If it's the booster canister itself, that is a little more work, but very doable. But if you're hearing it in the cabin at the brake pedal then it's probably the booster itself gone bad.

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