1989 Ford Aerostar Oxygen Sensor

JOE L.

MEMBER
1989 FORD AEROSTAR
6 CYL
2WD
AUTOMATIC
215,000 MILES

Cargo van, 3.0L. Complete Ford long block installed 70000 mi. Ago. Rebuilt (completely)A4LD Trans. Recently. Runs GOOD, major tune up 25000 mi back. Problem passing smog last 3 times. (Every 2 yrs) New cannister purge valve installed and has high NOX emissions per Ca. Smog check computer. Code reader says Ho2 not switching and always lean. New o2 sensor helps (a little) and then we barely pass Timing right on. I don't think we need a new o2 sensor every 2 years!(3 times now) No one seems willing or ABLE to tell me the problem. Any possible answers will be checked. Veh is privately owned, not commercial and is my daily driver, approx/ 10-12000 per yr. Max. Any help appreciated!

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Has high NOX emissions per Ca. Smog check computer. Code reader says Ho2 not switching and always lean

Causes here may include a defective EGR valve, EGR vacuum solenoid or motor, plugged EGR ports in the manifold, over-advanced ignition timing or engine overheating.

A lean fuel condition can be caused by:

* 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)