In my ongoing efforts to find out why Bank2 is lazy (new O2's, swapped old ones etc so its not the sensor itself), I metered the voltage coming from the two upstream harness connectors. I used an unneeded O2 pigtail and added some wire so it would dangle down, unplugged the O2 and connected this pigtail. Started engine and measured voltage w/ digital meter.

On both "12v" lines coming "into" the O2 (were it connected) I got a fluctuating voltage max 12, lowest around 0. Same for both harnesses. I also metered the heater circuits. Got similar voltage fluctuation, but max volts was about 7 or8.

Since one O2 sensor works flawlessly (according to my Xcal datalog), my assumption is that the voltage readings (same for each side) are ok. Can someone verify for me what the voltage signature should really look like coming down through the harness? Is there a more professional way to meter voltage on these harness connections?

I thought for sure I was going to find an anomaly as there isn't much left to test. No intake or exhaust leaks, fuel pressure and vacuum seem ok. Injectors don't seem to be leaking (fuel pressure remains constant after turning off the truck). I figured there was a bad signal coming into the Bank 2 sensor.

Any guidance would be appreciated.

 

The RIGHT way would be to tap the wires with the HO2Ss connected normally, or to use a scantool that can read those PIDs thru the PCM. Read this caption:

 

Actually I have scanned it quite a bit with my xcal2. Bank 2 upstream shows a very lazy sensor, mostly running rich. Even with replacement sensors, it shows the same thing. I was trying to figure out if the harness or maybe the computer was sending a bad voltage or maybe the harness had a bad ground that was causing the O2 to report erroneous voltages. Since both sides seemed to have the same voltage activity, and Bank 1 works fine, I was thinking something just on that side of the motor such as , intake/exhaust leak, wiring or PCM.

I recently read a TSB on another forum and there is a tiny paragraph that states:

# Do not compare HO2S switch rate - Bank-to-Bank or vehicle-to-vehicle: Different HO2S switch rates, from Bank-to-Bank, are considered normal. The HO2S switch rate, from one Bank to the other, should not be compared as a gauge of the HO2S's ability to switch/react. The PCM is continuously adjusting spark and fuel in reaction to engine operating conditions (rpm, load, air flow, throttle angle, etc.). The PCM is also continuously adapting to certain conditions (customer driving habits, engine and component wear, etc.).

here is the link to the general TSB:

http://www.ford-trucks.com/tsb/fullt...php?tsb=01-9-7

I dunno, maybe everything is OK. I did get a weird code not long ago -P2198 stuck on rich, which is the general behavior I had been monitoring. Cleared the code 3 weeks ago and have not seen it since.

Maybe I am chasing a ghost.

 

I wouldn't waste time diagnosing a NON-fault. Just do good maintenance for now.