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George H.
George H., ASE Certified Technician
Category: Lincoln
Satisfied Customers: 18763
Experience:  15+Years of service as a Master Technician
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Lincoln Town Car Signature Limited: what do the codes p0171

Resolved Question:

what do the codes p0171 and p0174 mean
Submitted: 5 years ago.
Category: Lincoln
Expert:  George H. replied 5 years ago.

Hello I will help you with your question,


These are lean fuel mixture codes and on your 4.6L engine are usually caused by one of the vacuum hoses getting soft and failing or the mass air sensor in the intake air ducting getting contaminated or failing. It is usually the large vacuum hoses attached to the throttle body though.


Let me know what I can do to help you with this





Customer: replied 5 years ago.
my vacume lines are in good shape could there any aditional things that may cause these codes the engine falls on its face when trying to accel
Expert:  George H. replied 5 years ago.

If the engine dies when you accelerate it indicates a large vacuum leak or the mass air sensor is not seeing the extra airflow or the exhaust is clogged not letting the air flow out of the engine.


On this engine the vacuum hoses are the prime cause, the PCV line often has a hole at the elbow on the back of the throttle body.


Sometimes the intake gaskets leak, you can try spraying water along the seams and see if the idle stumbles. You can also try brake cleaner but it is flammable so if it hits a spark it will flame up.


The mass air sensor is expensive, try unplugging it and see if the engine responds better, it is not a decisive test but it may show a bad sensor.



For the exhaust hold the idle up at 2500 rpm and if it starts chocking as the exhaust builds up it is clogged.


Let me know what questions you have


Thank you



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