Im at about the end of my rope on this one. BTW the ford P1151 is lean condition on the drivers side bank. I had 2 OBS 97 F250 hd's. Both unabused,cherry, 460, auto truck. The first was a 2wd, at 143K miles a P1151 shows up. Runs great but can smog here in Kali so in it goes. $500+ later, a fuel system cleaning and what ever else and all is good..for 1000 miles. 2 new upstream 02 sensors and back on the road again and I sell it to buy the 4wd. Now the other 97 identical truck but 4wd is doing the same thing. Between me and 2 shops we..check for vac leak, replace the 02 sensors, check the MAF and clean,bla,bla,bla, short of having the black box I do what I can but no luck. Shop #1 says while driving it they see the feedback from the 02 sensor go from normal to flat and back while on a test drive. They installed a used Motorcraft 02 sensor and it was OK for 6 cycles then back to the 1151. I needed the truck back so I pulled outta the shop. What the heck, ford sxxxx and giggles I install 2 new ford upstream 02's, no change. Weeks later its at a different shop I know better cause I give up. Days later and this shop thinks it a wiring harness problem and there time to tear into it. I have my reservations on this as I find it hard to believe 2 of the trucks I own have the same problem, at the same mileage. I cannot be the only unlucky fool with 2 trucks with this problem. In light of hundred of pages of ford 1151 code fixes I have yet to read about a bad wiring harness causing this issue. Throw me some ideal, anything before I loose what hair I have left on my noggen

 

Have you done basic things like check the fuel pressure? What are the short term and long term fuel trims?

 

The Front sensors are tested continuously for switching during Closed Loop operation provided the Conditions are met. Excessive time between switches, or no switches, indicates a malfunction. Since the lack of switching could be caused by fuel trim shifts as well as a sensor malfunction a stored DTC indicates whether the sensor was always indicating lean or rich when it stopped and if the Fuel Trim was at max.
Where Lack of Switch DTCs are recorded the LT Fuel Trims should be watched closely - if these show well into the negative or positive at idle they could be caused by an air inlet leak or a faulty Fuel Pressure Regulator - meaning that the fueling has not changed rather than the HO2S not detecting it. Before changing front HO2S sensors - particularly if there are any starting issues, check the connector voltage. and clean the connector well. Yours tested lean, lean = about 0 volts.
Best way is to hit the prongs w/lacquer thinner and then blow it out promptly w/compressed air. If you don't have compressed air to assist, use something less barbaric, like say a good electric cleaner medium/fast vap. Use a dry brush after to remove residual residue. There's always going to be some. Reason being, if the connector was somewhat dirty after your 02's were changed. Dirt/sand grains could have eventually compromised the connection. So before spending the cash, do the free stuff first.

Also thoroughly clean mild/any corrosion from the factory O2 harness with a small pick and electronics cleaner ... inspect O2 wires and harnesses for damage or corrosion...clean/tape.