1996 Ford F-150 emmisions testing

LUKEKELLOGG

MEMBER
1996 FORD F-150
6 CYL
2WD
AUTOMATIC
169,000 MILES

I cant get my check engine light to stay off so I can pass emmisions testan register my truck. I have a 96 ford F150 the codes say it is running lean I have replaced the vaccum lines I put a new intake manifold gasket and O-Rings on it I put a new mass air flow sensor on it and have replaced both O2 sensors and I clear the codes and drive it 30 miles and the check engine light comes back on I could really use some help dont know what esle to do.

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

A lean condition can be caused by:
1. Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle).
2. Dirty fuel injectors. (Try cleaning the injectors)
3. Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum).
4. Leaky EGR valve. (Inspect operation of EGR valve)
5. Leaky PCV Valve or hose. (Inspect valve and hose connections).
6. 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).