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P0171 vacuum leak into crankcase

Dturn1

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Ok, first post but I have been working this issue for a while. The car is a 2002 GTP 3.8 SC all stock. I have a P0171 fuel trims are bad LT 16.41 ST 10.43 goes to perfect at high rpm. I have smoked it and smoke dumps out the oil fill immediately. Checked the PCV and it is good. I even plugged it off. The leak is elsewhere. Pulled the valve covers and check for leaks at the valve seals and just pulled the intake and supercharger and replaced gaskets. I smoke the crankcase and pulled plugs to verify it is not the rings. Where else could I be getting this massive vacuum leak. I am missing something and could use some insight. Thanks if you made it this far.
 

Dturn1

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I have verified it is a vacuum leak and it is into the crankcase. I am trying to figure out where it may be outside of the PCV valve and gaskets. I do thank you for the reply and your input.
 

melsg5

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How are you performing the smoke test?
Why donr you also have P0174?
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melsg5

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No other codes?
No other problems with anything else such as braking?
You base the crankcase vacuum leak because of the smoke out the oil fill?
 

Dturn1

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That is my only code. No braking issues. I have smoked the entire system looking for a vacuum leak since the fuel trims go to zero with throttle input. Numbers and responses for O2s look good as does maf and map. Even at that there should not be smoke coming into the crankcase, especially with the pcv plugged off. Dropped the oil pan and it is not coming from the rings and pulled valve covers and valve seals are not leaking either. The car runs great other than this code. In addition the trims stay crappy cold and hot. I am not sure where or what else to look for.
 

Dturn1

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Not too proud to admit when I am screwed up. I was missing the PCV bypass at the throttle body outside of the butterfly. That is my leak into the crank case. With that plugged and no excess smoke, I have found a small leak at the egr tube where it meets the egr valve.
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melsg5

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Ok, that sounds much better, could not imagine any other leak attributable to the crankcase. Glad you found it.
 

Dturn1

New member
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Solved and confirmed fix. The honeycomb screen before the maf was missing. I bought one on Ebay and the fuel trims dropped back to normal. They now average +/- 1. This was surprising after having found and fixed all vacuum leaks and still had the issue. The sharp bend in the tube from the air box to the throttle body causes air turbulence at the maf. Hope this helps someone else.
 
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