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2004 Ford Ranger 3.0L Automatic Fuel Too Rich - P0172/P0175 Code Diagnosis

Model: Ford Ranger Fault Code: P0171 Posted: 2020-05-08 21:03

My 2004 Ford Ranger with a 3.0L automatic engine runs normally until around 4000 RPM, where it begins to run too rich across both fuel banks. The OBD2 diagnostic shows a 'fuel too rich' code (P0172 and P0175). I've already replaced the mass air sensor and air filter, checked for vacuum leaks, and confirmed the transmission control switch is out of self-test range. Despite these steps, the issue persists. What should I check next to resolve this problem? I have a scan tool available for real-time data collection.

Related fault codes
P0171P0172
Comments (8)
Anonymous 2020-05-09 12:41

Can you confirm which specific codes are being triggered — P0172 and/or P0175?

Anonymous 2020-05-09 12:42

Do you have access to a scan tool? If so, check the oxygen sensor voltages in closed loop mode at idle, 150-than 3000 RPM, as well as short and long-term fuel trims.

Anonymous 2020-05-10 20:46

Yes, I have confirmed both P0172 and P0175 codes. I also have a scan tool for real-time monitoring of engine parameters.

Anonymous 2020-05-11 06:49

Check the voltage readings from both bank pre-cat oxygen sensors in closed-loop operation. What are the voltages at idle, 1500 RPM, and 3000 RPM? Also review short-term and long-term fuel trims during these conditions.

Anonymous 2020-05-11 07:12

Make sure to monitor oxygen sensor voltages specifically at 1500 and 3000 RPM to identify any irregularities in the feedback loop.

Anonymous 2020-05-11 11:07

I've encountered cases where a stuck open purge valve or leaking fuel injectors, or a vacuum assist fuel pressure regulator failure, can cause excessive fuel delivery and rich mixtures. These should be ruled out during diagnosis.

Anonymous 2020-05-12 23:31

A key detail I missed: the issue is intermittent and varies in severity — sometimes the truck runs perfectly fine, other times it's noticeably rough at higher RPMs.

Anonymous 2020-06-01 22:41

Follow-up update: I replaced the ignition wires, plugs, and coil pack. Since I carry around 300 lbs of tools and the vehicle is automatic, it was sluggish at low speeds. After installing a Screamin’ Demon high-performance coil, Livewires, and Motorcraft Platinum plugs gapped to 0.065 inches, performance improved dramatically — smoother idle, better low-end torque, and smooth power delivery up to 5500 RPM during downshifts. The check engine light has remained off, indicating the fuel-rich issue appears fully resolved. I'm pleasantly surprised it was that simple.