Q: 04 explorer 4.0 soho po171

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Bought truck non running,found broken rear timing cassette.I pulled the motor bought the expensive cam alignment set and everything went well changed all the chains and cassettes.put it back in it fired right up but runs quite rough and only code on it is a po171 fuel trim lean on bank 1.Checked for vacuum leaks pulled the intake and valve covers rechecked the timing,all good.Compression on bank 1 is 170,165 and 170.

My car has 101000 miles.
My car has an automatic transmission.

Hi there. The most common cause for the P0171 code is a vacuum leak. I would double check all vacuum line connections to eliminate this as the primary source of your issue. It is also possible that the intake manifold gaskets are leaking. Over time they get brittle and will not seal very well and will need to be replaced.The only other possible cause of this OBD-II trouble code is a MAF sensor or a oxygen sensor that is failing.

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