Fuel system or vacuum leak??
7 Answers
P0171 is usually a vacuum leak, smoke test the vehicle.
A vacuum leak or exhaust leak are also a possibility.
Did a full smoke leak down test with no noticeable leaks under 10psi of pressure as well...pulled the fuel injectors and all are testing correct resistance, all have power, all are brand new with 50 miles on them. Also have a New OEM fuel pump, New OEM MAF sensor, New NTK Cam & Crank sensors, New NGK coils and plugs, new valve covers, new intake, new full custom made BRM stainless steel exhaust...I'm stumped♂️
So, I took apart the whole top end of the motor, did a compression test, did a fuel pressure test & voltage drop test, cleaned all the fuel injectors, bought new plugs, swapped the upper the O2 sensors, swapped around the coils, changed all the vacuum lines...The car is running Beautifully and I couldn't be more happy..Fuel trims on all banks are perfect !!! Thank you all for your insight and help !!!