Exhaust note changed, Loss of power, vibration under load, EPC light

[torquewrench]

I'm hoping to get some help on an issue. Yesterday on the freeway after accelerating, the exhaust note changed to a much deeper tone. The exhaust sounds normal unless it's under any amount of acceleration and load. It also seemed as though the car was in a gear too high, but it wasn't.
This morning, I accelerated hard and the EPC light came on immediately. Then it wouldn't shift gears automatically (I could shift manually) , and the car would shake violently when trying to slowly accelerate. After 3K RPM, it would somewhat smooth out.

I don't have a VAG-com, but scanned with my generic scanner and it came back with cylinder 3 misfire. No big surprise. At this point, the idle was rough and the EPC light was on. I cleared the code as the car was running, and the idle smoothed out.
Still feels like it's in 5th gear when going 25 mph.

Does the EPC light cause the car to go into limp mode? If so, that would explain why I can clear the code and then continue to drive (with a weird exhaust note and low power under 3K)
The exhaust note has me a bit baffled. Possibly a timing issue? I'm going to see if anyone local has a vag-com and/or will replace the coilpacks as as starting point.

Anyone else experience something similar? Any help is appreciated.

2012 S4 ,DSG

[soltez]

You've got a clogged/failed cat.

[torquewrench]

You've got a clogged/failed cat.

I appreciate the reply, however I would think the secondary O2 sensor would tell the ECU that something is wrong and I'd get a code.

[brainpan]

Sounds like failed cats to me, my cats on bank 1 and 2 melted without any cat efficiency codes. Random misfires and EPC light under full throttle. I spent a long time chasing the problem and it seems like more and more people are running into this issue.

I'm now running jhm cats and so far the car is running well again, exhaust note change is a definite sign of failing cats.

Sent from my Note 5

[torquewrench]

Great. It looks like everything is pointing to the cats. And from what I hear, it's a big job. ECS has some reasonably priced cats at 440 that are legal.

[CELison]

Failed cat. I had both of mine fail. Same symptoms. No CEL

[torquewrench]

Failed cat. I had both of mine fail. Same symptoms. No CEL

Thank you for taking the time to let me know. Where did you buy your cats, and do you mind letting me know the cost to replace?

[CELison]

Thank you for taking the time to let me know. Where did you buy your cats, and do you mind letting me know the cost to replace?

There's a 8yr/80k warranty on cats. I had mine replaced by a dealer. Just had to flash it back to stock and take all the bolt ons off. If it's not throwing a code they might give you a hard time. I went up the dps with a borescope and showed them the cat that had come apart.

[fvijay]

Folks, I had the same issue on my Q5, wit the EPC and check engine lights coming on. The dealer tells me that I need to replace all 6 of my fuel injectors at a total cost of $2800. Dealer tell me that it is not the spark plugs nor its the ignition coil and so has got to be the injectors.
Any suggestions?

[Morritse]

Folks, I had the same issue on my Q5, wit the EPC and check engine lights coming on. The dealer tells me that I need to replace all 6 of my fuel injectors at a total cost of $2800. Dealer tell me that it is not the spark plugs nor its the ignition coil and so has got to be the injectors.
Any suggestions?

You have VCDS? Log primary and secondary O2 sensors as a graph on both banks and you can see if one of your cats is fucked up.

Unless your dealer did testing, they are retarded to assume injectors. If you can, look at which cylinder is being disabled and see if it's always ones from bank 1 or 2.

[torquewrench]

Folks, I had the same issue on my Q5, wit the EPC and check engine lights coming on. The dealer tells me that I need to replace all 6 of my fuel injectors at a total cost of $2800. Dealer tell me that it is not the spark plugs nor its the ignition coil and so has got to be the injectors.
Any suggestions?

I caution you and your dealings with your dealer. I have found too many "mechanics" only know how to scan for codes, and blindly follow a diagnostic manual without taking a second to think.
Let me tell you my experience with the dealer. Don't get in a situation like this:

Since the car was techically under the 80K cat warranty, I brought my car to the dealer. I typically do all my own work, but hey I'll leave it to them if warranty was doing it. (my thought anyway)

It was misfiring so bad it wasn't drivable, I had it towed. I gave them hints as to what the problem likely was, but naturally they went ahead and started from the top, charging me for a full diagnositic. I get why they do that. Then they started charging me for spark plugs (I just replaced them), coils (I just replaced them), then more diagnositics. I brought my car in with the exhaust off, so they thought it was lack of back pressure causing the misfire. LOL. I paid for them to install my exhaust, and same issue. They wanted to replace injectors and if that wasn't it, they wanted to start tearing into my head, thinking it was the valves. It had been a month at this point, and diagnostics/parts were over 1K. I asked them to do a backpressure test, they came back in 15 minutes saying they just did. Knowing they were lying, I went home and got my 1989 junker truck and loaded it with my tools. I was livid.
I had them push the car out to the parking lot so I could 'take a look'. I tore the car apart right there while their 'mechcanics' took smoke breaks watching. I connected a gauge to the o2 sensors and the gauge was pegged. The cat was plugged on the side of the misfire. Just to verify, I removed the pressure gauge and let the exhaust pressure flow out the O2 sensor bung. The engine could breathe, and the car ran smooth.

I'm not a confrontational person, and just wanted to solved the problem. I asked for the mechanic to come out - and he wouldn't. So much for working together on this one. The service manager finally came out and I showed him the pegged pressure gauge and how I could make the car idle perfectly when removed. He said "But there's no code showing that the cats are plugged". I lost my mind.

I had another shop replace both cats as there is no way I would ever let them touch my vehicle. Its difficult, but spend the time finding someone that actually knows how IC engines work.

[alexbai94]

I caution you and your dealings with your dealer. I have found too many "mechanics" only know how to scan for codes, and blindly follow a diagnostic manual without taking a second to think.
Let me tell you my experience with the dealer. Don't get in a situation like this:

Since the car was techically under the 80K cat warranty, I brought my car to the dealer. I typically do all my own work, but hey I'll leave it to them if warranty was doing it. (my thought anyway)

It was misfiring so bad it wasn't drivable, I had it towed. I gave them hints as to what the problem likely was, but naturally they went ahead and started from the top, charging me for a full diagnositic. I get why they do that. Then they started charging me for spark plugs (I just replaced them), coils (I just replaced them), then more diagnositics. I brought my car in with the exhaust off, so they thought it was lack of back pressure causing the misfire. LOL. I paid for them to install my exhaust, and same issue. They wanted to replace injectors and if that wasn't it, they wanted to start tearing into my head, thinking it was the valves. It had been a month at this point, and diagnostics/parts were over 1K. I asked them to do a backpressure test, they came back in 15 minutes saying they just did. Knowing they were lying, I went home and got my 1989 junker truck and loaded it with my tools. I was livid.
I had them push the car out to the parking lot so I could 'take a look'. I tore the car apart right there while their 'mechcanics' took smoke breaks watching. I connected a gauge to the o2 sensors and the gauge was pegged. The cat was plugged on the side of the misfire. Just to verify, I removed the pressure gauge and let the exhaust pressure flow out the O2 sensor bung. The engine could breathe, and the car ran smooth.

I'm not a confrontational person, and just wanted to solved the problem. I asked for the mechanic to come out - and he wouldn't. So much for working together on this one. The service manager finally came out and I showed him the pegged pressure gauge and how I could make the car idle perfectly when removed. He said "But there's no code showing that the cats are plugged". I lost my mind.

I had another shop replace both cats as there is no way I would ever let them touch my vehicle. Its difficult, but spend the time finding someone that actually knows how IC engines work.

One random question,

is the 8yr/80km as long as you bought the car from Audi? I purchased it CPO and my CPO warranty is up in 2019 but if they were to fail in 2020, if it's under 8 years they would still warranty them? Is that correct?

[Silver Streakin]

One random question,

is the 8yr/80km as long as you bought the car from Audi? I purchased it CPO and my CPO warranty is up in 2019 but if they were to fail in 2020, if it's under 8 years they would still warranty them? Is that correct?

It's a federal law/warranty across all cars. 8yr/80k miles. Nothing to do with Audi.

[jak77]

Had this happen to me on the freeway today. Pulled over, shut car off and tuned back on. EPC light went away and the car's been running fine since. Are failed cats the only thing to cause this?

[Morritse]

Had this happen to me on the freeway today. Pulled over, shut car off and tuned back on. EPC light went away and the car's been running fine since. Are failed cats the only thing to cause this?

These specific symptoms? Including the exhaust note change? 99% yes.

[jak77]

These specific symptoms? Including the exhaust note change? 99% yes.

Most of them. Cant say for sure the exhaust or not since I pulled over right away and restarted the car. If the cats are going, would it stop happening and then happen again? Or would it be continuous?

Only mods on my car are bolt-ons (exhaust and intake). So far. Its a 2014 with 45k on the odometer.

[Morritse]

Most of them. Cant say for sure the exhaust or not since I pulled over right away and restarted the car. If the cats are going, would it stop happening and then happen again? Or would it be continuous?

Only mods on my car are bolt-ons (exhaust and intake). So far. Its a 2014 with 45k on the odometer.

It's continuous. EPC will usually come on when you push the car a bit. You should scan the codes and post them here.

[Audibellybutton]

Are my cats bad? I’ve been doing a lot of digging to try to fix my misfire EPC issue

I recently had maintenance done, new injector o rings/seals, coolant crossover pipe and carbon cleaning etc

A few days ago I flashed my e85 map back on and tried to have some fun with it. The car would misfire whenever you get over 3k rpm or give it some load. Epc light come on and it runs like shit vcds scan brought the code P0302 misfire on cylinder 2 only so I changed the plug and coil, didn’t work. Also did a. Compression test it was fine.

Fearing it was e85 related I went back to 93 octane map and it seemed to run fine a little while and then the issue come back except now it’s p0305 misfire on cylinder 5 only

I flashed the car back to stock and now i haven’t been able to recreate the issue. Flashed the tune again and it came back. Another symptom I have is the car backfired on deceleration but it didn’t before. When I run the stock map it doesn’t backfire at all. Could these be a symptom of bad cats? It’s weird how the issue jumped from cylinder 2 on bank 1 to cylinder 5 on bank 2 and it’s always only one cylinder. It throws epc light but not mil

[ModItNow]

Are my cats bad? I’ve been doing a lot of digging to try to fix my misfire EPC issue

I recently had maintenance done, new injector o rings/seals, coolant crossover pipe and carbon cleaning etc

A few days ago I flashed my e85 map back on and tried to have some fun with it. The car would misfire whenever you get over 3k rpm or give it some load. Epc light come on and it runs like shit vcds scan brought the code P0302 misfire on cylinder 2 only so I changed the plug and coil, didn’t work. Also did a. Compression test it was fine.

Fearing it was e85 related I went back to 93 octane map and it seemed to run fine a little while and then the issue come back except now it’s p0305 misfire on cylinder 5 only

I flashed the car back to stock and now i haven’t been able to recreate the issue. Flashed the tune again and it came back. Another symptom I have is the car backfired on deceleration but it didn’t before. When I run the stock map it doesn’t backfire at all. Could these be a symptom of bad cats? It’s weird how the issue jumped from cylinder 2 on bank 1 to cylinder 5 on bank 2 and it’s always only one cylinder. It throws epc light but not mil

After I had new a carbon clean and injector o rings replaced I was having issues of loss of power. Ended up one of my injectors went bad, most likely from removing and cleaning them. I replaced just that one injector and solved issue. I am not sure if this is the case with your issue. But yes I would check the cats and anything fuel related. Clogged lpfp filter? I had to replace this in my car after running e85 for a while. Have you checked your plugs? They go bad a lot sooner when tuned. I change mine every 10k or so and gap them to .026"

Sent from my Pixel 4 XL using Audizine mobile app

[Audibellybutton]

After I had new a carbon clean and injector o rings replaced I was having issues of loss of power. Ended up one of my injectors went bad, most likely from removing and cleaning them. I replaced just that one injector and solved issue. I am not sure if this is the case with your issue. But yes I would check the cats and anything fuel related. Clogged lpfp filter? I had to replace this in my car after running e85 for a while. Have you checked your plugs? They go bad a lot sooner when tuned. I change mine every 10k or so and gap them to .026"

Sent from my Pixel 4 XL using Audizine mobile app

thanks. Just wanted to give an update in case any other forum lurkers run into this issue.

Turned out to be spark plugs, I was in denial of this because I changed all of them recently, and then changed the ones in the cylinder that misfired again, but it was. I have a valve cover leak that seems to got oil on the plug and fouled them pretty quickly.so far the issue is gone.