Typically diagnosing a lean condition in a vehicle is pretty straight forward. But what do you do when you’ve corrected any obvious faults and everything tests out? You call on the SureTrack Community for help. SureTrack community member drdiesel had a Ford Ranger in the shop where the check engine light would come on after driving about 20 miles. They repaired some issues but still had the light coming on. They posed the question to the community, and with the help of fellow community member Richard_C and others, they were able to resolve the issue quickly.
The following Community Fix summarizes the interaction between members of the community that led to the solution.
Vehicle
1999 Ford Ranger 3.0L
Title
P0171 & P0174, replaced rear main seal.
Complaint
Customer complains that the check engine light is on.
Diagnostic Steps Performed/Parts Replaced
Check engine light on with codes P0171 & P0174 Fuel System Lean Banks 1 & 2. Truck runs smooth, no power loss, just turns check engine light on for fuel system lean faults after approximately 20 miles. Smoked intake manifold and found leaks at EGR and from crank case. Replaced both intake manifold gaskets and EGR valve. Smoked again and no leaks present. Road tested and light came back on in approximately 20 miles. Replaced sluggish downstream O2 sensor and MAF sensors. Light still comes on. Replaced fuel filter and tested fuel pressure runs 48-50 psi while driving and 52 at idle. Inspected exhaust for leaks and found no leaks. Cleared keep alive memory and road tested again and light came back on.
Best Answer from Community Member Richard_C
If correcting the fuel pressure doesn’t fix it, also check the PCV valve and how much vacuum it pulls when you remove the oil filler cap. Should have only a small hint of vacuum.
Cause
Rear main seal leak caused extreme vacuum leak in PCV system.
Correction
Replaced rear main seal leak, road tested vehicle and check engine light did not come back on.