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Discussion Starter #1
I have an 05 I4 5 speed with a K&N intake. For the last several months I have been getting a P0171 every time my fuel gets down to about 1/4 tank. I put fuel in and drive a while and the CEL goes off. I've searched for solutions but can't seem to nail it down. No leaks with K&N, MAF cleaned, throttle body cleaned. Has anyone else had this problem.
 

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P0171 means Fuel System Too Lean (Bank 1)

What this means is the the ratio of fuel to air is too high in the combustion chamber of the engine. Odds are you've got an air leak that's creating a lean condition. Put the OEM intake back on the engine and see if the problem goes away. Check your intake manifold bolts and make sure they're not loose. Cleaning your mass airflow sensor (MAF) may also help. This code could also indicate that your O2 sensor in bank 1 is faulty.
 

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Discussion Starter #6
P0171 means Fuel System Too Lean (Bank 1)

What this means is the the ratio of fuel to air is too high in the combustion chamber of the engine. Odds are you've got an air leak that's creating a lean condition. Put the OEM intake back on the engine and see if the problem goes away. Check your intake manifold bolts and make sure they're not loose. Cleaning your mass airflow sensor (MAF) may also help. This code could also indicate that your O2 sensor in bank 1 is faulty.
Do you know what would be the reason it only happens when the fuel gets low? Are any of these more likely than others? Any chance it could be fuel pressure related?
 

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I ran my k&n intake for years before I got it tuned. Never threw a code.
 

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Just brainstorming here, but could the low fuel level also relate to lower fuel pressure available which could lead to less fuel being injected and thus causing the lean code? Maybe something like a fuel pump or a pressure regulator.

This is also going to seem like a dumb question, but when was the last time the fuel filter was changed?

All this is assuming the problem continues after reinstalling the stock intake.....
 

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Discussion Starter #12
Just brainstorming here, but could the low fuel level also relate to lower fuel pressure available which could lead to less fuel being injected and thus causing the lean code? Maybe something like a fuel pump or a pressure regulator.

This is also going to seem like a dumb question, but when was the last time the fuel filter was changed?

All this is assuming the problem continues after reinstalling the stock intake.....
Did it before and after fuel filter change. I also was thinking fuel pump or pressure regulator might be the problem. I was hoping someone had experienced this before that might know.
 

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The problem is fuel related and apparently the level of fuel is the trigger. Could there be some kind of contaminate in the tank that is drawn to the pump inlet only when the quantity is low?
 

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Discussion Starter #15
Replaced the fuel pump last weekend and then went ahead and replaced the fuel pressure regulator too. So far no P0171. I'll see how long this lasts.
 

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Did your cel come back? I had the same issue and I thought a fixed it with a new MAF but its been on and off for the last couple of months. I cant seem to track the issue down but it only comes up when I am idling for an extended period of time. Im thinking its a pressure problem but I am unsure of how to check it. Just want to know if I am going down the right rabbit hole.
 

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Discussion Starter #17
Did your cel come back? I had the same issue and I thought a fixed it with a new MAF but its been on and off for the last couple of months. I cant seem to track the issue down but it only comes up when I am idling for an extended period of time. Im thinking its a pressure problem but I am unsure of how to check it. Just want to know if I am going down the right rabbit hole.
No cel since the change. Probably driven around 1000 miles since since changing the pump and regulator. Mine only came on when the fuel level was low (around 1/4 of a tank). I'm pretty sure it was a weak pump. It had around 290,000 miles on it!
 
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