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Q: engine codes p0171 p0174 p0325 p1000 on 1999 Ford Explorer

engine lights are on they told me to change the knock sensor, however the parts store gave me the egr sensor?
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P0171 and P0174 are lean fuel codes - P0325 is a knock sensor code. Ignore the P0325 for now, as it may be related to the fuel issue.

Look for vacuum leaks with the lean codes. Specifically - on this engine - if it's the SOHC 4.0L V6 - it is notorious for failure of the intake manifold o-ring gaskets. I would guess that the leak is there.
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