Mazda 6 Forums banner
41 - 45 of 45 Posts

·
Registered
Joined
·
155 Posts
Or it means that when at low RPM there is enough of a leak that it is not sending it downstream to be picked up by the downstream sensor.
I hope it works out for you.(y)
After fixing the exhaust leaks the fuel trim for Bank 1 has dropped from 10 percent to 4 percent which is good I think. There is an improvement in the O2 sensor waveforms as well. For low RPMs O2 sensor 2 waveform is nearly constant while sensor 1 wave oscillates. When I accelerate the O2 sensor 2 starts oscillating with sensor 1 somewhat but they aren't in sync like they would be if cat was doing nothing. Given this I think its prudent to wait on replacing the bank 1 cat. Since the engine fuel trim is in normal range and there are no misfires the risk that it will breakdown suddenly is low I hope.
 

Attachments

·
Registered
Joined
·
155 Posts
After fixing the exhaust leaks the fuel trim for Bank 1 has dropped from 10 percent to 4 percent which is good I think. There is an improvement in the O2 sensor waveforms as well. For low RPMs O2 sensor 2 waveform is nearly constant while sensor 1 wave oscillates. When I accelerate the O2 sensor 2 starts oscillating with sensor 1 somewhat but they aren't in sync like they would be if cat was doing nothing. Given this I think its prudent to wait on replacing the bank 1 cat. Since the engine fuel trim is in normal range and there are no misfires the risk that it will breakdown suddenly is low I hope.
@DrFeelGood I found that the test for catalytic converter efficiency must be done at Idle after the catalytic converter has reached operating temperature. Since I am seeing no inversions on the 2nd 02 sensor of bank 2 under this test condition the Bank 2 pre-cat is good and there is no need to replace it.
 

Attachments

·
Rally Racer
2004 Mazda 6s Wagon ATX
Joined
·
3,855 Posts
Discussion Starter · #43 ·
@DrFeelGood I found that the test for catalytic converter efficiency must be done at Idle after the catalytic converter has reached operating temperature. Since I am seeing no inversions on the 2nd 02 sensor of bank 2 under this test condition the Bank 2 pre-cat is good and there is no need to replace it.
Excellent. If that is without a non-fouler in place for sensor two it is then a watch and wait scenario. Maybe check back from time to time to see if it has changed. 🤷🏻‍♂️
 

·
Registered
Joined
·
155 Posts
Excellent. If that is without a non-fouler in place for sensor two it is then a watch and wait scenario. Maybe check back from time to time to see if it has changed. 🤷🏻‍♂️
I agree. Yes, this is without a non-fouler. I have a non-fouler only on bank 2 O2 sensor 2 which always shows a flat line with a hollow pre-cat. I always have a bluetooth OBD II connector plugged in so its easy to see the diagnostics on the phone.
 

·
Registered
Joined
·
155 Posts
Excellent. If that is without a non-fouler in place for sensor two it is then a watch and wait scenario. Maybe check back from time to time to see if it has changed. 🤷🏻‍♂️
Check engine light for P0421 went away after driving 30 miles with the leak fix. So ECU is happy with the improved waveforms :) Here is the leak fix I did along with tightening the flange bolts more. The white gasket sealer is mostly Koalin which is the same clay used porcelain objects. Since it's baked now it should last a long time I hope. I had to put a parabolic heater under it for 4 hours set it otherwise it was soft even the next day in cold and wet weather here. The setting time in the instructions is 2-4 hours.
 

Attachments

41 - 45 of 45 Posts
Top