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Old 01-12-2010, 08:42 PM   #1
norcal85
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Unhappy P0171 System too Lean (Bank 1)

Last week I started up my focus and it sputtered and died. I started it up again and was on my way. I've noticed that when idling it feels like it's going to die but it hasn't yet. It runs great on the freeway but when I pull up to a light, it feels a bit underpowered. I few days ago the check engine light came on and I checked the code

P0171 System too Lean (Bank 1)

Is this a Mass Air Flow sensor issue? Anyone have any ideas? Where is the MAF sensor located on an 01 Focus?

Thanks

P


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Old 01-12-2010, 09:06 PM   #2
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A P0171 is usually a vacuum leak. But, there are many possible causes. What engine do you have?

-----------------

P0171 - System to Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit.

For lean and rich DTCs:
Fuel system
Excessive fuel pressure.
Leaking/contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Vapor recovery system.
Induction system:
Air leaks after the MAF.
Vacuum Leaks.
PCV system.
Improperly seated engine oil dipstick.
EGR system:
Leaking gasket.
Stuck EGR valve.
Leaking diaphragm or EVR.
Base Engine:
Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2Ss.
A SHRTFT-1,2 PID value between -25% to +35% and a LONGFT-1,2 PID value between -35% to +35% is acceptable. Reading beyond these values indicate a failure.
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Old 01-12-2010, 09:28 PM   #3
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It's a DOHC 4-Cyl. 2.0 Liter 16V. If it's a vacuum leak i should spray water on the hoses and look/listen ?
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Old 01-12-2010, 09:54 PM   #4
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Quote:
Originally Posted by norcal85 View Post
It's a DOHC 4-Cyl. 2.0 Liter 16V. If it's a vacuum leak i should spray water on the hoses and look/listen ?
If it runs good on the highway, then you can probably eliminate the following items.

For lean and rich DTCs:

Fuel system :
Low fuel pressure or running out of fuel.

Base Engine:
Cam timing.
Cylinder compression.


Which leaves.....

For lean and rich DTCs:
Fuel system
Excessive fuel pressure. (not common)
Leaking/contaminated fuel injectors. (could be.)
Leaking fuel pressure regulator. (do you have a strong fuel smell under hood?)
Vapor recovery system. (do you have a light fuel smell under hood or near the tank?)

Induction system:
Air leaks after the MAF. (very possible - check #2 check the big hose between the air cleaner and engine, is it tight, no cracks?)
Vacuum Leaks. (very possible - check #3 is there a noticeable sucking noise from under the hood when engine is running at idle that goes away at full throttle?)
PCV system. (maybe, could be a cracked hose, or stuck valve, It's just another source of vacuum leaks, would also have some sucking noises.)
Improperly seated engine oil dipstick. (CHECK THIS FIRST!)

EGR system:
Leaking gasket. (vacuum leak too)
Stuck EGR valve. (this might be difficult to diag DIY, no noise, no odors, you need a diag tool, or remove/inspect.)
Leaking diaphragm or EVR. (another vacuum leak)
Base Engine:
Oil overfill. (CHECK THIS FIRST WHEN CHECKING DISPSTICK)
Exhaust leaks before or near the HO2Ss. (Also difficult to diag DIY, can you smell exh fumes under hood? Noisy under heavy acceleration?)
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Old 01-13-2010, 04:17 PM   #5
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http://www.focusfanatics.com/forum/showthread.php?t=220670

Use that thread to help you troubleshoot/ solve your problem

MAF sensor is located on the tubing of the Air Intake system. If you think its bad, you can test it with the volt meter.
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