Hey Folks, I would appreciate your help on this one.

I am getting a CEL after about 15-20 minutes driving. No drivability problems, seems a bit down on power on the hwy. First time the CEL has come on while driving since I bought the truck.

KOEO Codes - 111 System Pass, Code 172 HEGO Lean in stored memory.

I started looking for vacuum leaks, found that the HVAC control was leaking. So I capped that vacuum circuit, and test drove. CEL came one, same code results.

I checked the fuel pressure at the rail at idle, part throttle, WOT and then pulled the vacuum line from the FPR. Pressure ranged from 30 to 40 psi and behaved as it should.

So I bit the bullet and replaced all of the factory vacuum lines. Been on the to do list but haven't ever gotten around to it. Put a gauge on the vacuum tree just to see how it was behaving with the new lines. HVAC Circuit still capped. I also replaced the brake booster line and pcv line while I was at it. Showed steady 18 (inches mercury) at idle, and behaves as it should as the throttle moves and at WOT.

Truck idled smoother than it ever has since I have owned it, but the CEL light still came on and the codes did not change.

The ECT checks out, and is new Ford unit. The oxygen sensor (replaced with a Ford unit last year) looks good on visual inspection, harness had some oil on it but it hadn't penetrated the weather seals. I cleaned the harness just in case, but no change. I pulled the the EGR position sensor, and didn't see any carbon build up. The EGR, EGR tube, and position sensor were replaced with Ford units last year when I replaced the exhaust manifolds.

I have not checked the ACT, and it is next on the list. Any other thoughts on what to check next or if I should dig deeper into anything mentioned above let me know.

Sorry for the novel, but thought it best to be thorough.

 

Clean up the O2 sensor connector real well with with non contact electrical cleaner. Non-chlorinated brake cleaner works in a pinch. Make sure the wiring isn't burnt up.

Had a code 172 that persisted even after sensor replacement. Turns out an old leaky oil pan gasket had done some damage to the connector. I replaced the connector and all is well now.

Good luck

 

Thank you for the suggestion BLDTruth. I checked and cleaned the O2 Sensor connector again but it still did not help. I verified the EGR operation, ACT signal, and checked for gasket leaks again.

I consulted with my father and law and considering the lack of drivability issues brought us back to possibility that the O2 sensor could be the problem. I have replaced it and so far the CEL has not come back on. We will see if it lasts the week before I call it cured, but I am hopeful.