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Q: Truck runs smoothly with no misfires but CEL is on and bank 1 is running too lean.

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I have a 2005 ford F150 (5.4L 3-valve Triton V8). Last week my check engine light came on. took it to autozone to get the OBD reader on it. there were multiple piston misfires. I got all new spark plugs and all new ignition coils, and replaced them all myself (didn't break a single plug) and today I took it up to autozone AGAIN because my CEL came back on. Now they're saying my fuel filter is bad and I need a new one. No big deal it's $20. and they also said bank 1 is running too lean. Possible cause was labeled as a bad MAF sensor. I've spent about 5 hours on the internet gathering as much knowledge I can about this P0171 thing but I need the opinion of someone who knows about this kind of stuff.
My car has an automatic transmission.

A: Hi there. The P0171 code singles out bank 1...

Hi there. The P0171 code singles out bank 1; the airflow meter feeds both banks and if it was at fault you would codes for bank 1 and bank 2. Congrats on not breaking any of the spark plugs and this was probably a good maintenance move on your part. However, why did you replace the coils? Without a coil actually failing or using an oscilloscope to view the electrical operation, there was no need for their replacement. How does Autozone know the fuel filter is bad? Did they test fuel pressure before and after finding that the pressure was too low after the filter? Remember, the code is for bank 1 and anything that feeds both banks probably is not the cause. Autozone is there to do one thing, sell parts. Restricted injectors, a stuck O2 sensor, or a stuck variable valve timing system can create the lean code as well as misfires on one bank. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several technicians available that can assist you with a check engine light inspection.

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