This is a well maintained 2007 Subaru with 140k km on the 3.0 litre six cylinder EZ30R engine. She's running a little scratchy most noticeable when cruising although no codes or anything.
I decided to take a look at the airflow situation and noticed bank two seems to be running richer with less responsive data for the pre-cat wideband AFR and post-cat oxygen sensor.
Couple of screenshots attached we can see AFR on bank two is less responsive and also the O2 sensor reaction on bank 2 can be a second or two delayed compared to the bank 1 signal.
I understand the two banks won't be perfectly in sync but more than a second difference seems long with EFI. Could be a normal situation too I guess. Perhaps this is an airflow problem internal to the engine.
Some tests I've done;
- Switched sensors between banks, no change
- Smoke tested exhaust and intake, no leaks
- Replaced exhaust with a junkyard system as mine was rusty, no change
- The removed exhaust didn't have signs of oil or or coolant cleaning
- Checked fuel trims, all 3% or lower
The graphs below show data sampled at 20 rows per second;
Appreciate your help. I'll post responses and comments, hate to see a question die here.
EDIT 2019/06/16 Removed previous propane graph to save space. Adding results of my next propane test from @Zaid's help. The propane bottle may have been running a little low but the results tie in with @Zaid's image regarding a bad cat. Also added a chart showing AF & O2 sensors whilst driving steady and gentle on the highway, bank #1 O2 sensor is all over the place!
EDIT 2019/06/20 Now logging STFT to find bank 1 is cycling additional STFT at cruise, would this mean an air leak someplace ?