Another week has gone by and I'm still stumped.

Some of you may have seen that I started a related thread over on dweb, hoping to get some different people to weigh in.

Used dielectric grease on O2 sensors -- Uh oh

Today I set up the Ultra Gauge to display O2 volts in addition to fuel trims. I'd begun to think there might be a problem with the ECM and that it was just a coincidence that the codes appeared appeared at the same time I was making the changes with the dielectric grease.

After having more than a few times cleaned the connectors as carefully as I could I took the truck for a short drive today. The Bank 2 voltage was consistently low right away, as soon as the sensor got heated and began putting out anything at all. On the other hand the Bank 1 voltage was switching normally and the STFT was normal. For the first 3 miles. After that Bank 1 voltage fell to low levels, never getting above ~0.25-0.30 volts.

To me this means there is continuity to the ECM and that the ECM is not bad, but I could be wrong. I have two new O2s on order but I'm not sure why, since I expect the same problem will return.

Ideas welcome. Thanks.

 

I just went thru this same thing earlier this week. Whose O2's are you installing? I have gone thru a bunch of BOSCH from amazon and they were bad out of the box or failed inside 90 days. I had a long talk with Doug at AB and he mentioned that the standard replacement in the UK are the Walker sensors that they sell and are priced the same as BOSCH on amazon. I was told the other day by amazon that they are tired of getting complaints about these O2's and are considering not selling them any more.
I think the original O2's ( which are BOSCH) are made in Germany not in the US. I am wondering if there is a quality control issue with the US made ones. I installed the Walkers and will see how they work. No dielectric grease applied.

 

I'll spare y'all most of the gory details from the last two weeks but I think my truck's problem is solved. Mostly.

After installing a different pair of new sensors the problem persisted, although on Bank 2 only. I had bench tested both new sensors out of the boxes with a propane torch and both were switching normally. I bench tested the Bank 2 sensor again after the test drive and it failed the test. What could have caused an O2 to fail so quickly?

I stepped away from the truck for a couple weeks, partly because I had other things going on but also because I was again stumped.

Yesterday I again bench tested the failed sensor and to my surprise it tested fine so I reinstalled it and went driving. I had three trips yesterday and got no codes. STFTs were fine too, but I'd setup the UG to show O2 volts as well as fuel trims. I noticed that Bank 1 volts were switching normally but Bank 2 was switching more slowly. By that I mean it would read ~0.65 volts for 30 seconds or so and then drop low to ~0.20 volts for another 30 seconds. That continued back and forth all day, but Bank 2 STFT was switching normally.

So this morning I swapped the sensors side to side and took it for a drive. Just like yesterday Bank 1 volts were switching normally but Bank 2 was again slow. That left me scratching my head. Why would Bank 2 switch slowly if it isn't the sensor?

At this point I think I'll leave well enough alone for now and see what happens since it's not throwing codes and STFTs are good. The truck will be driven more later this week - stay tuned.

 

Okay, time to wrap up this thread.

I still don't know why or how a new sensor appeared to fail right away and then worked fine a few days later. Maybe the sensor was fine all the time and it was a matter of adaptive values adjusting over time. Who knows.

But the final matter of Bank 2 switching much more slowly than Bank 1 turned out to be "pilot error."

The truck gets driven only occasionally these days. Every time I drove it over the last four weeks it ran fine, fuel trims looked great, and there were no codes or pending codes, but Bank 2 O2 volts continued to switch more slowly than Bank 1.

Then when out for a drive yesterday I happened to look more closely at the Ultra Gauge. I finally noticed that in my hurry to set up the O2 voltage displays I'd set up the DOWNSTREAM O2 for Bank 2!

I corrected that error and I am happy to report that both sides are switching normally! All is well.

Moral of the story? Haste makes waste, I suppose. That and double-check your work, and make sure the tool being used to measure something is being used correctly.

 

Rover, I have asked this question on the forum and never gotten an answer. What are the correct fuel trims? At what state do you decide you have correct fuel trims? Idle after reaching op temp? Idle after driving and stopping? When?
Which ones LT or ST give the correct benchmark?