strutaeng

Ok, gotcha. I guess what I was trying to get across but forgot is that there are no fuel trims for the lower oxygen sensors. There's just LTFT and STFT for each bank. Maybe it's just the way that scanner is setup. A lot of them are universal so they may have a data that does not apply to some vehicles.

Were you getting any codes since you mentioned emmision tests?

marktm250

Now I get it. I just assumed there should be sensor 2 STFT data since they have a data entry point - then "n/a%" makes sense!

No codes - the only indicators are that the evap and O2 sensors are not ready. These two have been consistent for hundreds of miles and a number of drive cycles. I'm using "Car Scanner" on my iphone, but have not purchased the "pro" package. Wondering if the upgrade will allow me to do the bidirectional testing you've suggested. Is there something fairly obvious to look for about the O2 sensors on the data dumps?

strutaeng

I'm not familiar with that app or if the pro version has bidirectional capabilities.

As far as the O2, look at the waveform. It should oscillate from about 0.1V to 0.90V in a sine form. If you are not getting codes, then they are most likely okay.

Check out one of these videos from these guys on EVAP systems for GM vehicles:

marktm250

I disconnected and cleaned the O2 sensor cables - upon reconnect and scanning, I lost both S1 signals and check engine light came on with low voltages and lean run codes. After disconnecting, pushing harder on all wires, it appears all the connections are now working and the O2 sensors are doing the wave thing. I cleared codes, so now I have a bunch not readies back again. I'm thinking now's the time to disconnect the battery and start fresh - which has seemed to work to ready the O2 sensors in many cases.

I'll get back after I'm able to "drive cycle" tomorrow!

strutaeng

Can you clear the codes with your scanner app? BTW, the downstream don't do that sine waveform, but you should see the graph change when you flip the throttle.

The drive cycle for every ECU check should only be like 30-40 miles in my experience.

marktm250

I've cleared codes, disconnected the battery, reconnected and did a drive cycle. No DTCs, but now 3 not readies - cat htr, evap and O2 sensor. Going to do a cold start tomorrow morning to see if the cat htr sets. Going for a 100 mile trip this weekend - we'll see if the others ready up - or at least the O2 sensor so I can get it passed. If there's any specific readouts I should look for, let me know.
Thanks for all your help.

marktm250

After several drive cycles this morning, only the evap and O2 sensor are not ready. At least I'm back to where I started! I'll be driving quite a bit over the holiday weekend, so if there's anything I should be monitoring with my app, let me know.

marktm250

Some new data when engine warmed up and kept between 2000 and 2500 rpm for over 5 minutes:

• both upstream O2 sensors oscillate rapidly between 0.1 and 0.8 volts
• both downstream O2 sensors stay quite steady at .74 volts
• both banks STFTs range at -0.6 to +1.5 %
• both banks LTFTs stay at -0.7%

A good educational article I've found states this indicates a consistently rich mixture, likely due to ignition issues of some type. No indication of such as the engine performs very smoothly and great acceleration.
I'll recheck after my 100 mile trip this weekend.
Any tips appreciated (no $$s required)

strutaeng

Huh? Those fuel trims look perfect!

Where are you finding that these are a rich condition? 🤔

You are supposed to add up the LTFT and STFT and they ideally sum to 0, or as close to 0. You are very close to 0. I don't see anything wrong with your data.

The ECU has capability to continuously monitor and make instaneous fine adjustments based on fuel trims. Around+/- 15% is when it triggers the "money light." On my trucks when I check if they are around less than 3-5% I call it good.

marktm250

This is the article:
https://www.vehicleservicepros.com/s...sfire-concerns

It's possible I've miss-interpreted, but this was the statement:
"This happens so consistently that you can look at the datastream during the misfire event and if STFT has changed less than 15 percent positive and the downstream oxygen sensor has voltage higher than 650mV that you can with confidence look for an ignition related concern to be the cause of the misfire."

Even if this single "test" that I did indicates a rich condition, I'm certainly not sure it has anything to do with the O2 sensor not readying. Simply a confusing data point?