Repectfully request advice: Low O2S2 voltage & high LTFT caused by bad Catalytic Con
vehicle: 2011 Cruze LT 1.4L turbo, 67K miles (This car was not properly maintained by the previous owner.)
Long Term fuel trim ~ 12.7
O2S2 (down stream O2 sensor) voltage .67
vacuum at idle after warm up ~ 16"-17" Hg
vacuum at 3000 rpm increases to ~ 20" Hg and snaps to 26" when throttle position goes back to idle. Vacuum then returns to 16"-17".
Vacuum and long term fuel trim go down when AC is on and load percent goes up from 18% to 32%
Long term fuel trim goes down to ~ 3.5 when engine is at 3000 rpm.
This is classic indication of vacuum leak.
After replacing the AC Delco throttle body gasket with the MAHLE G32627 gasket my engine pressure leak down time from 15 psi to 5 psi is 31 seconds. This is an improvement of 14 seconds from the 17 second leak down time with the ACD OE gasket that came with the new intake manifold. (I must order the check valve bypass kit from Extreme Revolution to fix bad PCV design in new intake manifold.)
I cannot find a vacuum leak with propane, spray bubbles, or starting ether. I have yet to fabricate and use a smoke generator.
My question is can a partially malfunctioning low efficiency catalyzing catalytic converter cause a low O2S2 voltage that results in a high long term fuel trim? I think there's too much oxygen in the exhaust because there's unmetered air getting into the intake, but if a partially bad Cat can cause high LTFT, then how can that possibility be checked?
Please forgive my ignorance. I've long thought catalytic converters could not malfunction unless they were clogged or melted or the internal matrix was broken. Mine is not clogged and was not melted or broken or restricted when I had it out of the car and washed it out with soap and water.
Perhaps I need to go to Harbor Freight and buy a laser thermometer to check the input and output temps of my car's first Cat. By visual inspection, I am unable to see oxygen sensors on the down stream Cat.
So off to Home Depot I go to buy and empty paint can from which to fabricate a smoke generator.
Thanks in advance and Best Wishes for Continued Success.