2015 Chevy Silverado P0171 and P0174 Lean Both Banks - Hesitation on acceleration

Question

My truck is throwing both P0171 and P0174 codes and feels like it's struggling for power when I pull away from a stop. The idle is also getting really rough once the engine warms up. I noticed a slight whistling sound coming from the top of the engine bay when I blip the throttle.

Rachel Nguyen · Accepted Answer

Found the issue was a cracked intake manifold gasket and a split PCV vacuum line. I performed a smoke test and saw smoke billowing out from the passenger side lower manifold rail. I replaced the intake manifold gaskets (ACDelco 12626354) and the PCV tube assembly. Torqued the manifold bolts to 89 lb-in in two passes. Total cost for parts was about $85, and the fuel trims returned to +/- 3% immediately.

Greg Walters · Answer

Take a look at the PCV hose and the intake bellows. The plastic on these Ecotec3 engines can get brittle and crack under the clamps where you can't easily see it.

Carlos Diaz · Answer

You should check your fuel pressure too. A failing high-pressure fuel pump (HPFP) can cause lean conditions on these direct injection motors, though usually, you'd see a P050D code as well.

garagegrease · Answer

Check your Long Term Fuel Trims (LTFT) at idle versus 2500 RPM. If the trims improve significantly at higher RPMs, you definitely have a vacuum leak behind the throttle body.

2015 Chevy Silverado P0171 and P0174 Lean Both Banks - Hesitation on acceleration

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