Oxygen sensors going bad?

[djcodeman]

Random misfire at high rpm... p0300

Changed spark plugs
Going to do cat deletes tomorrow w big daddy defoulers

Did some idling in the driveway and took some live readings of o2 sensors.

I thought it was strange to see some negative voltage

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[engineermike]

The negative is sensor 1 (wideband) current which I believe is actually the heater current.

Otherwise this isn’t a valid test because you need to log during a cat test.

Secondly just a cautionary note that most don’t know is that the rear o2 sensors are used to calibrate the fronts. You can fool the cat monitor test using anti-foulers but you can’t fool the calibration. And since the cat brick is gone, the rears will be incorrectly biased which leads to calibration of the fronts to be wrong, which leads to it running richer or leaner than what the widebands say. This can be fixed in the tune by disabling FAOSC but many tuners and even tuning software don’t even allow this anymore, and even if they did you would perpetually be stuck in “not ready” status of the cat test.

 

[djcodeman]

The negative is sensor 1 (wideband) current which I believe is actually the heater current.

Otherwise this isn’t a valid test because you need to log during a cat test.

Secondly just a cautionary note that most don’t know is that the rear o2 sensors are used to calibrate the fronts. You can fool the cat monitor test using anti-foulers but you can’t fool the calibration. And since the cat brick is gone, the rears will be incorrectly biased which leads to calibration of the fronts to be wrong, which leads to it running richer or leaner than what the widebands say. This can be fixed in the tune by disabling FAOSC but many tuners and even tuning software don’t even allow this anymore, and even if they did you would perpetually be stuck in “not ready” status of the cat test.

So what would you suggest?

 

[engineermike]

So what would you suggest?

Personally I’m a proponent of keeping the cats. I’ve had good luck running stock gt500 cats (so far). The only people I know who have made it work correctly without them had to go into the tune and make changes at the binary level and had a deep understanding of the rear o2 sensor signal and how the calibration is done. Otherwise you’re stuck an inaccurate A//F ratio.

 

[djcodeman]

An update.... this morning while cruising to work in 6th gear I went WOT briefly and got these codes... p0300 p0302 p0304

Since they are all on the same bank 1 , I'm pretty confident its my upstream bank 1 o2 sensor.
I was also logging and will review the fuel trim activity in a bit.

 

[Zrussian13]

Might want to look at the intake manifold for cracks too. Seems common on these as they age and they throw codes like you have.

 

[djcodeman]

Might want to look at the intake manifold for cracks too. Seems common on these as they age and they throw codes like you have.

Running a roush blower. Turns out passenger side cat was melted. Now I have a p0155 code, will be swapping the o2 sensor tomorrow

 

[Zrussian13]

Running a roush blower. Turns out passenger side cat was melted. Now I have a p0155 code, will be swapping the o2 sensor tomorrow

Well that was dumb on my part. I guess I should have paid better attention to your first post!

 

[silverbullet85]

Hopefully no damage was done, clogged cats can easily destroy an engine in a hurry

 

[djcodeman]

Hopefully no damage was done, clogged cats can easily destroy an engine in a hurry

No doubt. I'm glad i caught it when I did.

 

[djcodeman]

Pics of the 2 cats

 

[HKusp]

There needs to be a solution to this FI cat situation and it needs to be a lot cheaper than buying a set of $3800 GT500 cats and having to hack them up. Someone at one of these companies needs to see the need and the solution will make them very popular very quickly.

 

[engineermike]

There needs to be a solution to this FI cat situation and it needs to be a lot cheaper than buying a set of $3800 GT500 cats and having to hack them up. Someone at one of these companies needs to see the need and the solution will make them very popular very quickly.

I agree. I’ve picked up a couple sets of used ones for $600-800 a pair and modified the car to accept them as a bolt-in and so far they've held up well. But there are limited used sets out there and not everyone can do the exhaust mods I did. There needs to be an aftermarket bolt-in solution that uses high performance ceramic bricks.

 

[Pistol_91]

There needs to be a solution to this FI cat situation and it needs to be a lot cheaper than buying a set of $3800 GT500 cats and having to hack them up. Someone at one of these companies needs to see the need and the solution will make them very popular very quickly.

The only solution i found was to completely get rid of them. Problem solved

 

[HKusp]

The only solution i found was to completely get rid of them. Problem solved

I too have done that, but it's not really a solution as far as from a tuning perspective and for those of us that have to do emissions testing.

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