1999 Chevy Silverado economy/codes

BROKENARROW

MEMBER
1999 CHEVROLET SILVERADO
V8
4WD
AUTOMATIC
186,000 MILES

I noticed in Nov. My fuel useage went from 18-19 to 15mpg highway. In Dec. It got real cold and a service engine light came on. P171, p174. Too lean both banks. I replaced plugs (that were not bad but wanted to spend money anyway LOL) changed air filter! Thats where I found a huge pile of fresh weeds from a mouse making a nest in there. Also replaced fuel filter and oil etc. I thought I found the problem with the mouse nest. Nope, in fact (its now -2 deg f) and I am now getting 13 mpg. The light came back on again and is reading same codes. Before I spend more needles cash and replace 0-2 sens. And maf could you please help me? Thank you very much

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

P0171/P0174 lean conditions

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)