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Discussion Starter #1 (Edited)
My 2003 F150 4X4 4.6 has the PO171 & PO174 cp codes.
Let me mention the truck is running great with the Check Engine Light on.
It's hard to tell if my milage has gotten worst with out doing the math, after all when I drove it off the lot I was getting 10 miles to the gallon, but after running full Synthetic Oil, got it closer to 12 (Funny huh)

After much reading, the first thing I did was removed the MAF and spray cleaned it (30 seconds of spraying) . I used a can of Mass Air Flow cleaner. Also new air cleaner installed.

Erased codes, drove 30 miles, same 2 codes are back.

Checked all hoses for vacume leaks, all look / feel good.

WWWellll, now I,m going for the 4 Oxygen Sensors.
Read many replies to posts made about these 2 codes and some of the (Top Gun Mechanics) write, " you wont get those codes (Bank 1 & 2 running lean ) and solve it with replacing the Up Sream (and/or) Down Stream Sensors.

It,s a bee-och replacing the o2 sensors (Up or Down stream), not to mention the $205 for the sensors and special 7/8 socket (which is definitly needed for replacing the down stream sensors).

I will let all know what the out come is! Any and all opinions appreciated.....
 

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Sounds like you're looking in all the right places already. Did you also verify that the air cleaner assembly was closed up like it should be? Those codes point to vacuum leaks though,m as you already know, they don't pinpoint a thing. I have looked at vacuum lines before and thought they were good only to replace them and discover they were bad but just not where I could see it.

Vacuum hoses, when compared to )2 sensors are too cheap not to try and replace them before you spend the time and money on O2 sensors. Just my two cents worth.
 

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Discussion Starter #3 (Edited)
I thank you for the second Idea , as the new o2 sensors did not make the fix. The Check Engine light came on after 20 miles with the all 4 new sensors.

Same codes> AGAIN
 
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