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Hey guys, so I have a 2001 Ford Explorer Sport with the 4.0 SOHC V6. I'm getting a P0172 and P0175 which I understand is a rich condition in both banks. My fuel mileage is abysmal now. I commute 70 miles everyday, and I dropped from 19-20mpg to 13-15. This leads me to believe it truly is a rich condition. I don't believe it's an O2 sensor issue, because if the computer was reading a false rich condition, it would actually lean out the fuel mixture and I would see an increase in fuel mileage. Since I'm seeing a decrease, I believe that the O2 sensors are actually reading a true rich condition, which the computer cannot remedy.

My long term fuel trims both sit around -22 at idle. It's trying it's hardest to lean out, but it can't. I've replaced the IAC valve, MAF sensor, spark plugs and wires, upper and lower intake gaskets, and air filter. I've checked all of my vacuum lines, and I don't see any obvious problems, however I haven't put a smoke machine on the intake system either to verify. I don't think I have any vacuum leaks, because wouldn't this cause a lean issue? The problem is too much fuel. Do you guys have any suggestions on where I should go next? I'm going to replace the EVAP canister tomorrow once the parts store opens, but I'm not sure that's my issue, because I unhooked the lines from it, and I'm still seeing -22 fuel trims. My guess would be a fuel delivery issue? What are the odds that an injector on both banks would be stuck open? The only thing I can think of that would effect both banks would be a fuel pressure issue? I'm thinking that maybe there too much fuel pressure, and so whatever the computer is commanding for pulse widths on the injectors is actually dosing more fuel than what the computer wants. Does that make sense? It's trying to lean out, but since the pressure is possibly too high, each opening of the injectors is more fuel than it's supposed to be, and therefore it can't lean out no matter what it does. I don't have a fuel pressure gauge so I haven't checked this. Just wondering if there's anybody that could give me a direction to head in. Thanks!
 
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