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Rear O2 0v at Idle

posted Jun 07, 2016 09:09:44 by Trex
97Ford ranger 4.0. I'm looking into a p0420. Believe the cat to be bad on this. Fully warmed up at idle the rear o2 Voltage is 0. 1500rpm it will start oscillating like the upstream. Return the engine back to idle rear o2 goes back to 0 Volts. Adding propane at Idle drives the o2 Rich. Is the 0 volts at idle fully warmed up normal?
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4 replies
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IvanKibuka-Kiguli said Jun 07, 2016 10:56:23
I think a warmed up downstream O2 sensor should hang rich (somewhere above 0.45V) at idle if the cat is good. Looks like you got yourself a bad cat.
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Dylan said Jun 07, 2016 16:36:28
Fully warmed up at idle the rear o2 Voltage is 0. 1500rpm it will start oscillating like the upstream. Return the engine back to idle rear o2 goes back to 0 Volts.


Like Ivan says. Classic bad cat symptoms...
Belgium, Europe
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Trex said Jun 09, 2016 16:42:49
Thanks!
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Tyler said Jun 10, 2016 00:49:24
Just for my info, is there only one catalyst (and one downstream O2) on this Ranger?

The only other thing I would suggest is checking for exhaust leaks between the upstream and downstream sensors. I have seen leaks very near O2 sensors cause them to read lean or respond slowly. Usually, this causes O2 performance codes, but still worth checking for anyway.
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