hello guys and gals im at a loss on this one. couple weeks ago I replaced pistons and rings on this and unplugged pcv orifice. it came back today running super lean 40% ltft, I checked fuel composition and came out to have only 10% alcohol. checked fuel pressure and found low side pressure low, 30 psi so I replaced fuel tank module. low side is now at 60 psi, test drove and still running super lean. tested injectors with afit to fit all were good and close to each other in flow. I unhooked evap purge pipe with no change, same with maf sensor. running out of ideas, thank you in advance

3.6 or 2.4?

Was there a compression problem, or oil getting by rings?

Have you pulled O2 sensor to check for contamination?

Sure there are no vac leaks? Did you check the exhaust for leaks?

Can you read O2 data on a scan tool?

brand new o2 sensor, good compression, smoke tested engine with no visible leaks

look for a cracked exhaust manifold,crack usually between 2&3 on the #3 runner up to the o2 sensor. If no vacuum,intake air leak or fuel issues possibly maf. Hope this helps.

If no fuel,intake air or vacuum leaks,check the exhaust manifold for cracks.usually on the #3 runner between #2 & #3 up to the o2 sensor. also could be skewed maf. Hope this helps.

Easy way to see exhaust leak, is pull spark plug out, add a couple drops of motor oil, put in plug, start car, and look for smoke coming from exhaust, in this case, manifold area....

Was this issue resolved? What did you find?

​​​​​​I am curious of and how you resolved this. I have rebuilt over 40 of these 2.4 Ecotec engines and I am having the same issue as you described. Mine is a 2010 2.4 Equinox. Complete rebuild including new GM pistons and rings, valve job on cylinder
​head, etc. Runs great. But has the P0171

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