Trouble diagnosing clogged / inefficient cats

[abamfo]

I'm trying to diagnose fouled or inefficient catalytic converters and would really appreciate any help... in fact, I'd be willing to offer a monetary incentive for someone who can provide me with a diagnostic solution and a log of what the rear o2 sensors should be performing like under different scenarios.

I have random misfires (usually while decelerating or under low load, rarely at idle), very rough idle 20 seconds after pulling up, no limp mode issues at WOT but engine takes a while to crank over in the morning... I have replaced the spark plugs, ignition coils, fuel pump, fuel filter, front o2 sensors, PCV valve, fuel injectors, as well as doing a carbon clean, compression check and vacuum smoke test with no luck.

If anyone has any ideas on VCDS which could help with diagnosing the cats I would greatly appreciate it... my car passed all of the readiness test on VCDS and I don't get any codes EXCEPT for "throttle body actuator" and "throttle body malfunction" when I reset DTCs and adaptions.

My cat temperatures are normally quite close to my exhaust temperatures, I have shown graphs in the excel linked below... and it appears that my bank 2 cat voltage jumps around a lot more than the other (as shown on chart below), which fits in with the higher LTFTs I get for that bank... and when I decelerate the front o2 lambda goes to 4 and the rear o2 volts goes to zero (should the rear o2 voltage hit zero this much?)

AT IDLE



WHILE DRIVING





All of the data I have logged is in the document below which outlines the various parameters (inlcuding misfires) at 1. IDLE, 2. NON-STOP DRIVING, 3. DAILY DRIVING

https://drive.google.com/open?id=0B2...FJzX1ppSnRFOEU

If anyone has any insights for me I would great appreciate anything

[BlownOne]

I got the throttle body malfunction code with a few others when I forgot to plug in the sensor after I put it back on the car. Might want to check the connector or possibly pull the throttle body and inspect that it moves freely.

[bhvrdr]

The only difficulty is that bad cats can also look like other ECS type failures as well. But in general you are on the right path. You're gong to see misfire activity, possibly a cat inefficiency code eventually, and possibly lean codes. If you are getting this activity, I would be doing the same thing and ruling out other emission control issues (ie, if you could narrow the misfires down to a single cylinder it may be a plug, injector/injector seal, cylinder leak, etc) and then if you have to visually inspect the cats, not a bad idea. Dealerships will replace the parts via the GFF process of elimination.

Throttle body codes can be tune related and shouldnt have anything to do with misfires. Can you easily return the car to stock just so you can rule out as much as possible?

Mike

[abamfo]

The only difficulty is that bad cats can also look like other ECS type failures as well. But in general you are on the right path. You're gong to see misfire activity, possibly a cat inefficiency code eventually, and possibly lean codes. If you are getting this activity, I would be doing the same thing and ruling out other emission control issues (ie, if you could narrow the misfires down to a single cylinder it may be a plug, injector/injector seal, cylinder leak, etc) and then if you have to visually inspect the cats, not a bad idea. Dealerships will replace the parts via the GFF process of elimination.

Throttle body codes can be tune related and shouldn't have anything to do with misfires. Can you easily return the car to stock just so you can rule out as much as possible?

Mike

Thanks for your input Mike. Yeah the shop (non-Audi) has asked me to put the car back to stock, minus the exhaust, and then try and diagnose it. Removing the supercharger pulley is the most expensive piece of the puzzle. I also have the lightweight crank pulley OEM size from JHM. I think my best bet might be to pull these parts off, put the originals back on, replace the crankshaft and camshaft sensors and then see how it compares.

If it is the cats it is very hard to diagnose without taking them off and it might not be bad enough to send any inefficiency codes to the ECU anytime soon. I don't get specific cylinders which misfire, it's spread throughout the banks. We checked all the injectors and seals when they were replaced. A cylinder leak would've been diagnosed when Audi did their compression check, I imagine. It isn't a leak in the intercoolers because I'm not losing any coolant and we did a compression check through the coolant reservoir.

Audi dealerships aren't particularly interested as the car isn't stock, has flagged a TDX warranty fault and has no codes for them to diagnose. The one part I keep coming back to is that as I pull up at lights or to park, the longer I wait the more the lumpy lump idle comes in and the fuel trims add more fuel. It makes me think that backpressure is building whilst at idle.

[abamfo]

I got the throttle body malfunction code with a few others when I forgot to plug in the sensor after I put it back on the car. Might want to check the connector or possibly pull the throttle body and inspect that it moves freely.

Surely the throttle body wouldn't have functioned at all with the sensor unplugged? I might take it out over weekend and re-inspect then

I do know that if my adaptions are reset, the car will not function properly without the throttle body adaption.

[fitzydude]

Surely the throttle body wouldn't have functioned at all with the sensor unplugged? I might take it out over weekend and re-inspect then

I do know that if my adaptions are reset, the car will not function properly without the throttle body adaption.

My car ran but misfired badly with that TB sensor not clipped in all the way, drove me crazy for an hour or so.

Also, I'm about to replace all my coil pack connectors. When those are cracked they can cause misfires, just a thought.

[abamfo]

My car ran but misfired badly with that TB sensor not clipped in all the way, drove me crazy for an hour or so.

Also, I'm about to replace all my coil pack connectors. When those are cracked they can cause misfires, just a thought.

This one?? As in the bottom left... I'll have a look

[timzcat]

For like $20 buy a usb borescope camera and drop the exhaust connection and feed it up there and see what the cats look like on the inside, easiest solution.

[fitzydude]

This one?? As in the bottom left... I'll have a look

My bad I believe it was the bypass valve connector.. Sorry
Btw I have a low mileage throttlebody I could sell if you ever need it.

[abamfo]

My bad I believe it was the bypass valve connector.. Sorry
Btw I have a low mileage throttlebody I could sell if you ever need it.

As in the clip, dead centre of that picture?

[abamfo]

For like $20 buy a usb borescope camera and drop the exhaust connection and feed it up there and see what the cats look like on the inside, easiest solution.

I've been thinking about this but I was worried that most of the damage might be at the top of the cat, then it would be a pointless exercise as you wouldn't be able to see it right?

I've read another thing you can do is attach a vacuum gauge to an old oxygen sensor (somehow) and put it in the front o2 sensor hole and test the backpressure at each cat. It does seem hard on our cars with limited space though.

[fitzydude]

As in the clip, dead centre of that picture?

Correct.

When did all this start happening? We're you doing something to the car and it started? Did it develop on its own? Then did it happen suddenly or gradually?

[abamfo]

Correct.

When did all this start happening? We're you doing something to the car and it started? Did it develop on its own? Then did it happen suddenly or gradually?

It's really hard to tell when the misfires happened as they aren't normally under WOT. When I bought the car (January) it had a rough idle but I read online (before finalising the purchase) that was normal and many people had the same with this engine but I wasn't able to check for any random misfires logged in the computer and the mechanic said there were no DTCs after driving it for an hour but didn't check the misfire log. EDIT: thinking about it now, I reckon it might have gotten worse during the couple of weeks I added in a little bit of E85. Do you think it could be something in the HPFP?

Ever since the rough idle and the misfire has been getting worse and worse, albeit the carbon clean and new injectors did help somewhat. I took it for a drive the other night for about 5 mins, then parked it whilst idling and felt like it was about stall and a misfire was logged, I suspect it runs lean at idle because it definitely doesn't run lean under WOT by the look of my exhaust tips. If I could get rid of the really lumpy / semi-stalling idle, I could live with 20-30 misfires here and there as long as the cat was cleaning the damage but I suspect that the issues are related.

The other issue is if the problem is worsened by my cats but they are not the answer, then it will happen again unless I fix the underlying problem. Any chance you have any logs of your B2 sensor voltages versus RPM? I'd love to see how they compare.

[abamfo]

Correct.

When did all this start happening? We're you doing something to the car and it started? Did it develop on its own? Then did it happen suddenly or gradually?

Just checked the clip and all is fine.

Interestingly, I did see the coolant level is back down again in the middle of the range and the week before last it was above the max line... how long should it normally take the coolant fluid to drop like that?

This may sound stupid but does the water in the coolant evaporate when the coolant temperature is above 100 degrees celsius (212 fahrenheit)?

[xpoweruk]

Have you considered the possibility that 1 of the Internal SC chargecoolers has a small leak ??

[abamfo]

Have you considered the possibility that 1 of the Internal SC chargecoolers has a small leak ??

It has crossed my mind but until today I didn't think that any coolant was being lost... we did a compression check by applying 20 pounds of pressure to the coolant reservoir and there was no movement in the coolant level after 15 minutes and when we re-gapped the spark plugs it didn't look like there was any coolant residue on them, which Loe had when he had that issue. Kicking myself that I didn't get the shop to check this out when they had the charger off.

The question for those more experienced that me is, would a leaking intercooler cause random misfires throughout the different cylinders on either bank? I would've thought not, surely it would only cause it where it was leaking. In particular, Loe did mention that in his situation it was causing knock in one cylinder and I tend to get it through all cylinders when appropriate. That being said, coolant in the combustion chamber and then in the cats would cause abnormal voltages which I do see.

It sounds like the only way to check the cats is to take them off... and realistically, backpressure tests wont work as I'm guessing the car won't run properly without going into closed loop with the o2 sensor plugged in

[timzcat]

So for coolant it obviously is at min level when cold and will rise when hot due to expansion. When it cools it will bring coolant back into the system from the reservoir. If you really think there might be a leak then not the cold level and the hot level over a series of days, but I am not thinknig so.

Back to my idea, the right camera would fit in the O2 hole also. Given you description I think you'd see some damage at the back end. The idea would be camera from rear and a strong light in O2 so you can see through the matrix.
I guess the question is what caused the cat to go bad. They don't typically go bad for no reason and something usually causes it which is often excess fuel from some other condition.
Regarding readings, non-catted O2 should be very active and catted O2 should reflect the same type of activity but at a lower reading. It is absolutely normal for an O2 to zero on decel because fuel is completely shutdown when the throttle is closed provide there is RPM to maintain the engine running. (ie higher RPMs). So a post cat O2 that shows little movement (especially in comparison to the other bank) is not seeing significant change in exhaust conditions suggesting a lack of flow. I am a little surprised it has never tripped a code if its lazy.
As far as driving scenarios, at idle you should see constant movement for example 2 to 8. The ECU is constantly triming fuel suppply to maintain the perfect ratio 14.7:1, there is no load. When you are on the throttle under load (moderate acceleration) the O2 is going to go high as the ECU compensates for the demand with fuel. 12:1 down to probably 10:1 under heavey acceleration. At cruise it should act like idle and be constantly trimming fuel for a perfect ratio. which is realistically 13-14:1 And as mention when you lift completely the whole system goes lean because there is no fuel until RPMs lower and the ECU begins re-adding fuel which will still show lean at say 2000 RPM because the engine is still pumping more air then idle but throttle conditions don't dictate fuel.

[timzcat]

First chart. Bank 1 doesn't drop like bank 2 when you close the throttle and then rises more slowly. Meaning the lean condition created at throttle closed is not seen by the O2 sensor. That is the post cat O2 reading?

I don't know Audi programming exactly but a misfire code is not an actual determination that it took place in ignition, its a determination the O2 conditions remained or more likely rose (rich fuel) even though fuel was trimmed. Its a conclusion that the cylinder is not firing or doing so inefficently.

Have you considered a cylinder compression test to determine cylinders are all relative? A bad cat can also potentially raise all cylinders on one bank due to the back pressure but at cranking speed it probably would show well.

Regarding back pressure you have no reason to be in closed loop, simple idle would show back pressure with the appropriate gauge. IIRC you need a manometer to do that test, psi is not sensitive enough.

[abamfo]

So for coolant it obviously is at min level when cold and will rise when hot due to expansion. When it cools it will bring coolant back into the system from the reservoir. If you really think there might be a leak then not the cold level and the hot level over a series of days, but I am not thinknig so.

Back to my idea, the right camera would fit in the O2 hole also. Given you description I think you'd see some damage at the back end. The idea would be camera from rear and a strong light in O2 so you can see through the matrix.
I guess the question is what caused the cat to go bad. They don't typically go bad for no reason and something usually causes it which is often excess fuel from some other condition.
Regarding readings, non-catted O2 should be very active and catted O2 should reflect the same type of activity but at a lower reading. It is absolutely normal for an O2 to zero on decel because fuel is completely shutdown when the throttle is closed provide there is RPM to maintain the engine running. (ie higher RPMs). So a post cat O2 that shows little movement (especially in comparison to the other bank) is not seeing significant change in exhaust conditions suggesting a lack of flow. I am a little surprised it has never tripped a code if its lazy.
As far as driving scenarios, at idle you should see constant movement for example 2 to 8. The ECU is constantly triming fuel suppply to maintain the perfect ratio 14.7:1, there is no load. When you are on the throttle under load (moderate acceleration) the O2 is going to go high as the ECU compensates for the demand with fuel. 12:1 down to probably 10:1 under heavey acceleration. At cruise it should act like idle and be constantly trimming fuel for a perfect ratio. which is realistically 13-14:1 And as mention when you lift completely the whole system goes lean because there is no fuel until RPMs lower and the ECU begins re-adding fuel which will still show lean at say 2000 RPM because the engine is still pumping more air then idle but throttle conditions don't dictate fuel.

Thanks Tim, I'm monitoring the level of the coolant more diligently now and only whilst cold. If there was a leak in the intercooler, I wouldn't know how it would cause the lumpy idle though.

I'm thinking more about your idea with the USB camera and I think I'll give it a go, I'll buy one today. With your comments around the 0.2v to 0.8v (assume that's what you meant) at idle constant RPM, I never see that. At idle, the voltage sits constantly just below 0.8v as you can see in the first picture on the right. At cruise it does move around more though. The front oxygen sensor switches from rich to lean at idle as it should, with fuel trims normally adding fuel at 5-10% using both ST and LT trims.

[abamfo]

First chart. Bank 1 doesn't drop like bank 2 when you close the throttle and then rises more slowly. Meaning the lean condition created at throttle closed is not seen by the O2 sensor. That is the post cat O2 reading?

I don't know Audi programming exactly but a misfire code is not an actual determination that it took place in ignition, its a determination the O2 conditions remained or more likely rose (rich fuel) even though fuel was trimmed. Its a conclusion that the cylinder is not firing or doing so inefficently.

Have you considered a cylinder compression test to determine cylinders are all relative? A bad cat can also potentially raise all cylinders on one bank due to the back pressure but at cranking speed it probably would show well.

Regarding back pressure you have no reason to be in closed loop, simple idle would show back pressure with the appropriate gauge. IIRC you need a manometer to do that test, psi is not sensitive enough.

Yeah the first picture was at idle using post cat o2 sensors (which are actually located inside the cat), while the second was whilst driving using all o2 sensors and engine speed. The voltages look more similar while driving than they do at idle

So if it isn't a determination that there was a misfire, does that mean it could simply be that there is a rich fuel condition? I thought misfires were determined using the position of crank using the crank position sensors

Audi did a cylinder compression check and found all to be within spec but didn't provide me any results.

[timzcat]

Usually an actual misfire is from a lean condition not rich. If you have an issue that is excessively rich then its possible to foul out the plug. Most often Cats go due to rich conditions because the excess fuel burning off in the cat destroys it.

My numbers were correct for standard O2 wasn't think Lambda.

[abamfo]

Usually an actual misfire is from a lean condition not rich. If you have an issue that is excessively rich then its possible to foul out the plug. Most often Cats go due to rich conditions because the excess fuel burning off in the cat destroys it.

My numbers were correct for standard O2 wasn't think Lambda.

Thanks again, based on your experience:

1. Would you say that the exhaust and cat temperatures should be the same at idle? Mine are always move to be the same at idle, to the exact same degree (around 475-500 degrees celsius)

2. I had the lightweight crank pulley removed today and honestly some of the vibrations at idle have gone but if you idle for more than a few minutes you can feel a lumpy idle come back. What else other than excess backpressure could cause this do you think?


Working on getting a USB camera to check in the cat, thought it might be too difficult to do with my experience but it doesn't look to hard to remove the sensor and look in the hole.

[CELison]

I went up the DP with a scope to diagnose my bad cats.

[miztahsparklez]

These are what my plugs looked like after about 25-30k

Sooty, so I'm guessing rich? I've been through multiple cats already...


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[Batman0424]

Subscribed - trying to sort out a similar issue and I am wondering if the cats are causing the my misfires.

[timzcat]

These are what my plugs looked like after about 25-30k

Sooty, so I'm guessing rich? I've been through multiple cats already...


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Sooty indeed. Looking at those though makes me think possibly burning some oil, how is your consumption?
Don't know the mileage but sounds like 60K? I'd also entertain carbon on the valves with the issue there being restricted air flow which wreaks havoc on proper intake air and combustion. Which can also create that rich look.

For guys who have done carbon cleaning I'd be interested to know if two cylinders were not as bad as others based on the better looking left of picture plugs compared to middle and right.

[timzcat]

I went up the DP with a scope to diagnose my bad cats.

Did that rattle or was it wedged in there?

[timzcat]

1. Would you say that the exhaust and cat temperatures should be the same at idle? Mine are always move to be the same at idle, to the exact same degree (around 475-500 degrees celsius)

I'd expect them to be, sitting still is going to equalize temps and since you are at idle it's not moving much air and fuel. I'm curious if you get he misfires mostly when you are flogging the car because under heavy throttle all stock tunes go pig rich and you end up processing more fuel in the cat. I see you are tuned so I can't speak to how rich the tune is. Obviously the reason is to prevent a lean condition under load which is catastrophic.

2. I had the lightweight crank pulley removed today and honestly some of the vibrations at idle have gone but if you idle for more than a few minutes you can feel a lumpy idle come back. What else other than excess backpressure could cause this do you think?


I won't talk talk about lightweight crank (non dampened) pulleys because I hate them for many reasons. Interestingly one of which is false positive knock sensor readings. No dampening of crank harmonics can be noisey.
Given the list of work already performed its hard to point at much else and given the post up the downpipe the camera may be your best bet.

[miztahsparklez]

Sooty indeed. Looking at those though makes me think possibly burning some oil, how is your consumption?
Don't know the mileage but sounds like 60K? I'd also entertain carbon on the valves with the issue there being restricted air flow which wreaks havoc on proper intake air and combustion. Which can also create that rich look.

For guys who have done carbon cleaning I'd be interested to know if two cylinders were not as bad as others based on the better looking left of picture plugs compared to middle and right.

My oil consumption gets worse after about 5k miles after a change. Usually almost none before 5k miles. Wonder if that can contribute to cat failure? Pcv valve has been replaced before around 35k or so.

Yeah it was about 65k or so? Was changed at 35k.

Hmm I'll have to check the carbon buildup when I get my water/meth kit installed.








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[abamfo]

1. Would you say that the exhaust and cat temperatures should be the same at idle? Mine are always move to be the same at idle, to the exact same degree (around 475-500 degrees celsius)

I'd expect them to be, sitting still is going to equalize temps and since you are at idle it's not moving much air and fuel. I'm curious if you get he misfires mostly when you are flogging the car because under heavy throttle all stock tunes go pig rich and you end up processing more fuel in the cat. I see you are tuned so I can't speak to how rich the tune is. Obviously the reason is to prevent a lean condition under load which is catastrophic.

2. I had the lightweight crank pulley removed today and honestly some of the vibrations at idle have gone but if you idle for more than a few minutes you can feel a lumpy idle come back. What else other than excess backpressure could cause this do you think?


I won't talk talk about lightweight crank (non dampened) pulleys because I hate them for many reasons. Interestingly one of which is false positive knock sensor readings. No dampening of crank harmonics can be noisey.
Given the list of work already performed its hard to point at much else and given the post up the downpipe the camera may be your best bet.

Yeah looks like the next step is using a camera to look at the cats, I'll let you know how it goes... I'd really like to test backpressure as well through the exhaust manifold but it seems quite difficult and hard to find good shops in Australia who are keen to help

Car very rarely misfires under WOT, it's normally while part throttle or coming off the throttle... car is tuned and does not run lean under throttle, misfires are normally logged when actual lambda is 0.95+... lambda at full throttle hits its lowest value of around 0.7 (AFR of 10), so car does run rich when I've got the foot down, maybe I put my foot down too often but there aren't any misfires at full throttle so I can't image there'd me much for the cats to clean up?

If anyone has any logs of what perfect 100% functioning cats looks (rear and front lambda vs engine RPM) at idle it might really help a few people diagnosing cat troubles...

[CELison]

Did that rattle or was it wedged in there?

No rattle. But I knew it was a bad cat the minute the exhaust note changed. That was my second one to fail. The other bank failed a few months before that one.

[timzcat]

Yeah looks like the next step is using a camera to look at the cats, I'll let you know how it goes... I'd really like to test backpressure as well through the exhaust manifold but it seems quite difficult and hard to find good shops in Australia who are keen to help

Car very rarely misfires under WOT, it's normally while part throttle or coming off the throttle... car is tuned and does not run lean under throttle, misfires are normally logged when actual lambda is 0.95+... lambda at full throttle hits its lowest value of around 0.7 (AFR of 10), so car does run rich when I've got the foot down, maybe I put my foot down too often but there aren't any misfires at full throttle so I can't image there'd me much for the cats to clean up?

If anyone has any logs of what perfect 100% functioning cats looks (rear and front lambda vs engine RPM) at idle it might really help a few people diagnosing cat troubles...

For the car to misfire under WOT it would have to be lean not rich. It would have to be so rich that it fouls the plug but that's flood rich and not going to happen because with DI there is good atomization and fuel doesn't get an opportunity to pool. So if the AFR is at 10 at WOT and you drive that way the cat is seeing considerable fuel on a regular basis. You say it misfires when you lift which I wonder is excess fuel firing off in the cat making the restriction worse. At that AFR you are not burning all the fuel, evident by the reading. Factory tunes are usually down around 10 because they don't want blown motors so they make the map artificially rich to keep cylinder temperatures down and prevent detonation. Being DI I would think that tune would be a little leaner like 12 but I cannot speak for any tuner and I have not been involved in Audi tuning just prior experience working with a tuner in the Evo world.

I am curious what would happen if at idle you plugged up the exhaust to see if it immediately started misfiring. Theory here is the bad cats are already causing a restriction in the exhaust and random misfire, if you make the restriction problem worse I wonder if it immediately replicates the issue. I know that would be difficult to do and with cross over in the exhaust you don't get the luxury of trying each bank.

Something worth mentioning is who replaced the plugs? I would pull them and check them not for the part in the cylinder but the insulator on the outside. Spark plugs are surprisingly fragile and its very easy to crack the porcelain. What you are looking for is any black lines in the insulator. Misfires on lift are lean out misfires which means there was likely a shorter path of resistance for the spark than a lean cylinder such as a flaw in the insulator.

The upside to a camera that has a smaller tip is you will be able to use it inspect other things such as piston condition.

[timzcat]

My oil consumption gets worse after about 5k miles after a change. Usually almost none before 5k miles. Wonder if that can contribute to cat failure? Pcv valve has been replaced before around 35k or so.

Yeah it was about 65k or so? Was changed at 35k.

Hmm I'll have to check the carbon buildup when I get my water/meth kit installed.








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That doesn't sound bad. Oil consumption can certainly foul a cat, gasoline is refined to burn clean and what the cat should see is minimal as far as unburned fuel. Oil is not refined to be burned and leaves behind residue.
When it comes to boost like turbo or supercharger the crankcase experiences more pressure, as a result the PCV is going to see more activity and likely oil. This is why there is a market for a catch can to create a place for oil to collect that will not be pulled into the intake system and only gases. I don't think that is possible on this engine but would reduce the need for carbon cleaning.