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Thread: oxygen sensor graph review help. Cat dead? Reply to Thread
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Topic Review (Newest First)
12-04-2012 10:43 AM
fast*st Well, rehash, the P0420 comes and goes, around town driving it comes on, If I take a highway run that's 2 tanks of gas or greater it goes off, though at some part throttle conditions it seems a little rough, have to investigate any vac leaks, time for the garden hose. It may be time to hit the boneyard, grab a chunk of an O2 sensor harness and put the resistor/cap in that versus chopping up a good sensor. Figure that'll give me matching male/female plugs and some wire leads.
02-07-2012 05:56 PM
fast*st Also read another bulletin on the focus that a P0420 could be caused by a high oil level? I checked and yeah, its a half quart or more over the line so did an oil change. I haven't seen the P0420 re-appear yet. Getting close to the 100 miles since reset so should be good for emissions testing soon.
02-06-2012 10:17 PM
fast*st Well replaced the front 02 sensor, it was about 90% jet carbon black. Also changed the pcv valve and inspected the rubber hoses, all seemed fine. Here is another strip chart, front sensor voltage is indeed a bit higher, scale is 0 to 1 volt.

Is the Focus SVT converter really 2 parts? It looks like Header, o2 sensor, oval cat segment, rear o2 sensor, then another bendy oval cat section before it bends up and around the axle.

I have seen the P0420 come and go once since
02-04-2012 09:34 AM
whynotthinkwhynot Let's see that graph after you replace bank 1.
02-04-2012 07:44 AM
fast*st Oddly enough, planning to pull the front o2 sensor and it has another code pending, #1 o2 sensor not switching enough, too lean. I pull it out and its pretty darned black, the old rear one was light tan, wondering if its been sending bad data or if I have a misfire that's not being caught.
02-03-2012 03:53 PM
Originally Posted by fast*st View Post
Yeah, P0420 showed up in 'pending' drat, maybe not letting it idle enough, usually start and go :) Suppose with a harness plug from the boneyard and the old O2 sensor plug part could make the resistor adapter, though willing to try and make it right.
Yeah if you can't tolerate the CEL I'd consider a cheater/emulator. The only cat failure that will affect performance is melting and that's a completely different scenario than inefficiency.
02-03-2012 01:39 PM
fast*st Yeah, P0420 showed up in 'pending' drat, maybe not letting it idle enough, usually start and go :) Suppose with a harness plug from the boneyard and the old O2 sensor plug part could make the resistor adapter, though willing to try and make it right.
02-03-2012 01:37 PM
Grinder Perhaps but the cat monitor isn't really comparing the front to the rear so much as just focusing on the rear during closed loop. Obviously it isn't looking closely in OL drive modes like WOT or extended idle but I've never heard of a bad (or brand new) front 02 erroneously setting cat efficiency codes.

If the light doesn't come back on I wouldn't worry much.
02-03-2012 01:34 PM
fast*st Right around 95,000 miles so far, seems the previous wrench discarded everything heat shield related. I've been getting brand gas from two stations (Mobil) not the econo place, I suppose a newer front O2 sensor could give a bigger split in the signals?
02-03-2012 01:07 PM
Originally Posted by fast*st View Post
Another thing I wonder about is that all the heat shields have been discarded from underneath, is it possible that at cruise throttle, the pipes are cooling off enough to not let the converter burn? After a run, stop and idle and the rear oxygen sensor drops to a flat line, the above graph was part throttle cruise. Normally on my commute I'm running about 1800 rpm 40 or so in 6th gear.
Meh. The shield is more to keep the heat away from grass and underbody than it is to keep heat in. Sounds like the cat is capable of storing oxy based on your post-cruise datalog.

How many miles?

It may be on it's way out but proper driving cycles and fuel quality will prevent the P0420 from repeating.

Also... I've noticed some non-oxy 91 around here. I didn't notice much of a difference but the switch rate threshold for your downstream 02 is calibrated for oxygenated fuel. It's possible that a batch of non-oxy on a worn cat could make that downstream switch high enough for the PCM to set an efficiency code.
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