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Q: Bank 1 is lean - 2001 Ford Mustang

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So I took my mustang on a trip about 4000 mikes and my check engine light came on. So I went to Auto Zone and the said that bank 1 is lean. So I replaced the MAF and I put in a new O2 sensor in Bank 1 Sensor 1 and I still have the light on. What normally make this light come on. I have no idea what to do now.

My car has 246000 miles.
My car has a manual transmission.

A: As you know, this is caused by a lean fuel ...

As you know, this is caused by a lean fuel condition. This can be caused by a few different things, one of which is a dirty or failing mass air flow sensor, which you have already replaced. The other potential causes may include: unmetered air entering the engine through a vacuum leak, an EGR valve that is not closing and is leaking exhaust into the intake manifold, or an EGR valve that is allowing too much flow. This may be caused by the EGR differential pressure sensor under-reporting EGR flow.

If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator, or dirty fuel injectors. I would recommend having an expert mechanic, such as one from YourMechanic, come to your location to determine why exactly the Check Engine Light is on and suggest any needed repairs.

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