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Discussion Starter · #1 ·
Chevy Trailblazer 2006 v6 I have replaced and checked and double checked EVERYTHING having to do with air flow through the engine and replaced fuel pump and evap canister, mass air flow, o2 sensor, air solinoid, intake manifold gasket, ran the SUV through a smoke machine and found No leaks. Yet the car keeps throwing p0171 and shakes badly to the point of stalling when at driving temp. Whats left???
 

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You have a lean condition on your air-fuel ratio.
No vacuum leaks, new MAF, new fuel pump, and still throwing a lean condition code, start looking at your fuel trims. If you see a more than two digit fuel trim correction on the plus side, look at the fueling control.
Could be clogged fuel filter or dirty fuel injectors.
Get a OBD2 scanner that shows live data on LTFT and STFT. (Long term and short term fuel trims)
 

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Sarah, your 4.2 V6 is actually an inline six (I6).
It's been my experience with these trucks, that 4 things can generate a P0171.
  • an air leak between the MAF and the throttle body.
  • an intake vacuum leak.
  • a sticking solenoid on the air pump,
  • and a dirty throttle body.

You've already looked at 3 of the items, try cleaning the throttle body, it causes a lot of problems on these trucks.

Note, disconnect the battery before you start remove the TB and carefully clean it, don't pry the butterfly.

After you put it back on and connect the battery, you may find it idles fast, disconnect the battery again to fix this.
Sometimes 2, or 3, disconnects are needed.

One other thing of note with these trucks is the exhaust manifold, it cracks under the manifold where the web comes together to exit. It will leak when cold and stop after the metal gets hot.
GM will replace this for free.
 

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Discussion Starter · #4 ·
You have a lean condition on your air-fuel ratio.
No vacuum leaks, new MAF, new fuel pump, and still throwing a lean condition code, start looking at your fuel trims. If you see a more than two digit fuel trim correction on the plus side, look at the fueling control.
Could be clogged fuel filter or dirty fuel injectors.
Get a OBD2 scanner that shows live data on LTFT and STFT. (Long term and short term fuel trims)
 
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