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OnlineHelp, Mechanic
Category: Car
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Experience:  Mechanic
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My 00 expediton 4.

Resolved Question:

my 00 expediton 4.6 has the code's PO171 and PO174
Submitted: 8 years ago.
Category: Car
Expert:  OnlineHelp replied 8 years ago.
Hello and thank you for choosing Just Answer.

P0171 and P0174 indicate that the car is running lean. What this means is that there is either too much air coming in (not detected by the Mass air flow sensor) or too little fuel. These codes do NOT means the oxygen sensors are bad.

I would suggest that you start by cleaning the mass air flow sensor to make sure it is registering the amount of air coming in correctly. If that does not solve your problem you will need to take the fuel pressure. The fuel pressure should be between 35PSI-40PSI (when started).

If the car is also not idling correctly you will need to check for vacuum leaks.
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