99 Tahoe/O2 sensors (upstream) defective?

[Kowalski]

Dear all,

I (almost) solved a rough idle condition of my '99 Tahoe 5.7 Vortec but still it idles not really smooth. As suggested by some here on this forum I purchased the Bafx-OBDII-scanner in conjunction with the Toque Pro-App.

I would like to ask you, whether my O2 sensors are functioning correctly. If idling at appr. 700 rpm there is first a steady line. I have learned that this is correct. If the engine warms up graphs are fluctuating - strangely, different from each other when looking at bank #1 and bank #2 sensors (before cats). Also when hitting the gas, graphs looking very different from each other.

Is there something that comes into your mind when looking at these screenshots?


Best whishes,
Kowalski

 

[Kowalski]

Here some more screenshots

 

[Big Mama]

Welcome to the forum from Virginia. This one’s out of my league but some experts will chime in.

 

[Kowalski]

Hi Steven,

thanks for welcoming me.

Virginia - beautiful state. When I was a sailor on containerships we called the port of Norfolk quite often. Interesting habour with all the navy vessels.

 

[exp500]

Greetings Kowalski. Denso O2 sensors are an inexpensive Fix here in USA. There does seen to be a fair difference between sides, Possibly switch sides to verify Upstream sensors if hard to aqquire there.
I would also look at long and short term fuel trims, especially at cruise speed. See if they vary between sides matching O2s. Trims should maintain 0-10 percent. 25 percent and up you have problem somewhere.
One of the best running trucks in my fleet of 12 has a small shake only at idle. So far all the normal fixes for that have had no change in that shake. There are some more things to try, but it is a work truck so that is low priority. As it is barely noticable. Rock Auto has a good parts search if having a part number is helpful to you getting part localy if they do not ship to you.