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Ford Ranger 4.0L Trouble Codes P0125, P0171, P0303, P0304 - Diagnosis & Solutions

Model: ford ranger 4.0L Fault Code: P0125 Posted: 2008-04-03 17:34

I have a 2000 Ford Ranger 4.0L V6 with persistent trouble codes: P0125, P0171, P0303, and P0304. I've already replaced the O2 sensor (addressing P0171) and cleaned the MAF sensor. I inspected plugs on cylinders 3 and 4 — they appear in good condition. The ignition wires are only 12,000 miles old and of high quality. I recently changed the fuel filter and performed an intake leak check using a spray test; no leaks were detected. The idle remains stable during testing but does not rise or drop when sprayed. I've also checked the EGR valve pickup tube — it's clean and appears functional. Despite these steps, the P0171 and misfire codes persist. I'm seeking expert advice on next steps: should I inspect the EGR system further? Is there a known cold-weather issue with this engine model? Any recommendations for diagnosing cylinder 3 and 4 misfires or a possible thermostat/coolant-related cause (P0125)?

Related fault codes
P0125P0171
Comments (2)
Anonymous 2008-04-04 05:13

Check the intake gaskets when the engine is cold. A leak can cause rich mixtures and trigger P0171, especially in colder climates.

Anonymous 2008-04-05 08:17

With the engine cold, I started the truck and let it idle at around 1500 RPM for about 30 seconds before it settled to 1000 RPM. My vehicle now idles consistently at about 800 RPM — much smoother than before. I sprayed the entire intake with carb cleaner; no improvement was seen, and I confirmed no spark leaks during a dark inspection. After cleaning the MAF sensor, the misfires worsened during driving. I'm planning to check the ignition coils and wires today, and will perform a compression test on cylinders 3 and 4. It's odd — the truck ran fine in Florida but now performs poorly in Michigan. I suspect it may not be handling cold weather well. Thanks for the advice — I'll keep sharing updates as I go.