Failed Cats Emissions Question

657 Views 7 Replies 3 Participants Last post by DaveDotNet, Apr 12, 2022

DaveDotNet

Discussion Starter · Apr 6, 2022

So I bought a car (2013 S5) which has 2 failed aftermarket cats. Hidden by a dodgy ECU flash. I didn't know this at the time.

I have gotten the car flashed back to standard and I'm getting catalitic bellow efficency errors now.

The car does smell quite fuely/fuemy.

I got a emissions test done and I'm failing.

Now I'm trying to work out if the car is running rich (I don't want to just replace the cats in this case) or if it's just the failed cats causing the high HC content.

With thr bellow readings whats the likelyhood of the car running rich or if it's just fucked cats.

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Pepito

· #2 · Apr 7, 2022

"2 failed aftermarket cats. Hidden by a dodgy ECU flash." That should be your alarm bells. I wouldn't trust an aftermarket cat personally.
Your lambda reading look ok on the emissions test but I would look at what the lamdba sensors are actually reading. If they look ok then the cats are the problem. The efficiency error is due to the fact the sensors aren't seeing the required O2 storage from the cats, not surprising if they are aftermarket. If you have the standard cats, I would put them on now that you have the standard tune back on.

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DaveDotNet

Discussion Starter · #3 · Apr 7, 2022

Pepito said:
"2 failed aftermarket cats. Hidden by a dodgy ECU flash." That should be your alarm bells. I wouldn't trust an aftermarket cat personally.
Your lambda reading look ok on the emissions test but I would look at what the lamdba sensors are actually reading. If they look ok then the cats are the problem. The efficiency error is due to the fact the sensors aren't seeing the required O2 storage from the cats, not surprising if they are aftermarket. If you have the standard cats, I would put them on now that you have the standard tune back on.

That's good to hear it's probably the cats. I don't have any standard cats atm but picking a pair up the weekend.

Shame it requires a gearbox drop!

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Dippy

· #4 · Apr 7, 2022

Are you sure that there are aftermarket cats fitted? Alternatively it could have been de-catted or had so-called "test pipes" fitted in their place.

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DaveDotNet

Discussion Starter · #5 · Apr 7, 2022

Dippy said:
Are you sure that there are aftermarket cats fitted? Alternatively it could have been de-catted or had so-called "test pipes" fitted in their place.

There are cats there just not standard.

She's quite loud too so she's either got aftermarket cats or they are gutted.

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DaveDotNet

Discussion Starter · #6 · Apr 7, 2022

Dippy said:
Are you sure that there are aftermarket cats fitted? Alternatively it could have been de-catted or had so-called "test pipes" fitted in their place.

Since I put my foot down a few months back (she's been parked up since) the car is blowing and reporting rich codes pre cat (left bank) and lean post so I think the back pressure from the failed cats has blown something.

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Pepito

· #7 · Apr 12, 2022

A simple thing to see what the issue could also be is the swap the sensors over between the banks. Does the code follow the sensor or does it stay on the same bank. It it follows the sensor then I would say the sensor needs replacing, if it stays on the same back then something else as gone wrong on that bank causing the rich running. I doubt backpressure has much to do with this as it is just a flow through cat and if its aftermarket its most likley a lower cell density than OEM.

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DaveDotNet

Discussion Starter · #8 · Apr 12, 2022

Pepito said:
A simple thing to see what the issue could also be is the swap the sensors over between the banks. Does the code follow the sensor or does it stay on the same bank. It it follows the sensor then I would say the sensor needs replacing, if it stays on the same back then something else as gone wrong on that bank causing the rich running. I doubt backpressure has much to do with this as it is just a flow through cat and if its aftermarket its most likley a lower cell density than OEM.

I'm just going to replace all 4 lambda sensors. I can get all 4 Lucas ones for £130. I purchased a pair of second hand oe cats too so hoping both those will fix the problem.

It's funny how the bank which is reporting the rich codes also sounds like the one which is blowing.

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