Mechanics

W/4.0L. RUNS ROUGH AT IDLE CODE 153 AND THE O2 SENSOR ON LEFT BANK NOT SWITCHING. ALSO SHOWS RICH ON SCAN TOOL. MASS AIR SEEMS TO CHECK OUT(VOLTAGE IS GOOD). NO VACUUM LEAKS I CAN FIND. REPLACED O2. DID NOT FIX.

1994 Ford Ranger • 120,000 miles

Checked for vacuum leaks, MAF sensor, fuel pressure, fuel pressure regulator. All check good.
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Rocky71
April 5, 2012.



Probable causes of an engine running rich are as follows: 1. Excessive fuel pressure can be cause by restricted fuel return line

2. Defective Oxygen Sensors.

3. Leaking injectors and fuel pressure regulator.

4. Coolant temperature sensor out of calibration.

5. Restricted air intake system.

Rasmataz
Apr 5, 2012.