EPC on acceleration. Potential spark/fuel/cat problem?

[jbritton]

Howdy all, I've lurked for a while but finally made an account after some funky goings-on while driving last night (plus a decent amount of planned future work).

I was on the highway, cruising up a mountain pass at 75mph (90 East, Snoqualmie for those who know/care). I stepped on the gas to pass someone (still in 6th), the car began to shudder, EPC light came on, and I took the next exit which was luckily close. Pulled off the side of the road, turned the car off. Got out, looked around, saw no leaks, no odd smells, fluid levels fine. Started up, engine sounded fine, but the EPC light was still on so I turned the car off again and sat for a few minutes, and got on the forums. Started up again, no EPC light, everything sounded fine, so I got back on the road and drove rather conservatively the rest of the way (about 120 miles) with no issues until I tried to pass someone again. This time it was a flat road, going about 55mph (in 6th again), and when I stepped on the gas (not lightly, but not flooring it) I felt a small shudder and something like a "blup" from the exhaust, so I let off, stopped the pass attempt, and everything went back to normal. Tried passing again with gentle acceleration and nothing bad happened. Got to my destination, turned car off, got on the forums again.

From what I've gathered reading the forums, this could be one of several things either:
-Coil packs
-Spark plugs
-Injectors
-Cat

I'm leaning towards a spark issue since this only seems to happen under relatively hard acceleration.

What do y'all think? Any and all help appreciated.



Car details:
I'm the third owner of my 2012 S4, 6MT, 103k miles, AWE exhaust (I think), upgraded supercharger pulley (unsure of brand). Work was done by first owner, I've had the car since 2016 and about 20k miles (I was gone a lot the first three years I owned it).

[Rodizzle]

Cats or Fueling ( lpfp) not injector.
Start with a scan , and if you replicate the problem I would log fueling .


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[jbritton]

Cats or Fueling ( lpfp) not injector.
Start with a scan , and if you replicate the problem I would log fueling .


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Had to look up lpfp. Is that like the sender? So you're thinking the fuel pump wasn't able to keep up with demand? I need to get a scanner...

[jbritton]

Also, if cats, would the issue just disappear like that? Last time I had a car with a cat failure I couldn't drive above 30mph. That was a 95 Jetta though so I'm not sure if it compares lol.

[Rodizzle]

Had to look up lpfp. Is that like the sender? So you're thinking the fuel pump wasn't able to keep up with demand? I need to get a scanner...

Scanner is a must with these platform , I would highly recommend you a VCDS .
As far as the LPFP(low pressure fuel pump ) , yes it’s the actual sender . But diagnosing it with out a scan is pointless . Like you mentioned it could just be a plug . .
Cats and lpfp have epc issues on passing up car WOT tho ... from experience.

-Ro


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[Rodizzle]

Also, if cats, would the issue just disappear like that? Last time I had a car with a cat failure I couldn't drive above 30mph. That was a 95 Jetta though so I'm not sure if it compares lol.

Iv has cats fail twice and both times let’s you drive normally . They tend to act up on WOT pass 4600 or so . You won’t even get a code related to the cats , just a damn misfire due to the disabling of cylinder the ecu .


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[jbritton]

What is WOT?

What kind of VCDS would you recommend? There's probably a whole thread about it I haven't found yet lol.

Weird about the cats, I guess something to do with it failing enough to have increased backpressure or something during acceleration, but not enough to affect the car otherwise?

I'll have to pay closer attention to my tach next time. I'm guessing I was somewhere around 4k.

Do you think there's any harm in trying to reproduce the issue? That consistent shudder the first time is what was really throwing me. Is that just what happens when EPC puts the car in limp mode? (Or however that works)

[fastboatster]

1. WOT = wide open throttle
2. VCDS is a tool available from Rosstech.
@Rodizzle - had a similar EPC light issue last weekend, when I tried to accelerate in 7th, it felt like the car would hesitate, the revs would drop a bit and then pick back up. This was happening at about 2500 rpms. After a few times to accelerate like this, the EPC light came on and the car started to shudder. When I pulled over it said cylinder 6 was misfiring and was shut down. Had to clear the code to drive away. Did I just win a lottery ticket and need to do my cats? That will be epic since I just reinstalled my transmission and was wondering if I should gut my cats while at it. Or could this still be something else? With this car, it's always the worst case scenario, I think.

[killer_s4]

Like ro said. Get a vcds cable.

If you want to start the cheap route take your plugs out and check condition/gap and go from there.

[fastboatster]

I have an OBD11 and bootleg ODIS, what would I need to log specifically? Also, I had the spark plugs replaced before that epc light came on, I mean all the spark plugs except for cylinder 6 (I lost the 6th spark plug since I stored them for a while), going to get that plug replaced, too. I can’t stop wondering if I somehow bashed my left cat too hard when I was manipulating the transmission under the car, I recall that the flange shaft bracket had a very small clearance with the left cat and sometimes the trans wouldn’t move forward because that bracket made contact with that cat. If that’s the case, looking at this from an optimist PoV, I will fear no cat failure no more and will go dual pulley.

[jbritton]

Oh, got it, VCDS is specific. And pricey. Are there similar products that aren't $400+ for mobile, or that don't require a laptop?

I'll probably start with spark plugs, but I gotta replace my clutch soon so I might as well do a cat delete while I'm down there. (I'm assuming those can both be done on jack stands.)

[hardfive]

Oh, got it, VCDS is specific. And pricey. Are there similar products that aren't $400+ for mobile, or that don't require a laptop?

I'll probably start with spark plugs, but I gotta replace my clutch soon so I might as well do a cat delete while I'm down there. (I'm assuming those can both be done on jack stands.)

3 vin ross tech VCDS cable is 199. Best bang for your buck.

[fastboatster]

Oh, got it, VCDS is specific. And pricey. Are there similar products that aren't $400+ for mobile, or that don't require a laptop?

I'll probably start with spark plugs, but I gotta replace my clutch soon so I might as well do a cat delete while I'm down there. (I'm assuming those can both be done on jack stands.)

Obdeleven is a mobile only product, its cheaper than vcds but I have to say vcds is better and has good support. Support is non-existent for obd11. As for the clutch job, it can be done on the jacks, however even if you can doesn't mean you should. Paying 10 hrs labor seems like a bargain to me for this job. Granted, mt is a bit lighter and less bulkier than dsg but it is huge and heavy, too.
P.S. going back to logging, what exactly needs to be logged? I keep my fingers crossed it's a spark plug issue but I honestly expect the worst case scenario which isn't too bad since it will allow me to go DP without worries. I'm just concerned how to pass CA visual smog inspection with O2 sensor spacers.

[jbritton]

3 vin ross tech VCDS cable is 199. Best bang for your buck.

Cool. How much does functionality differ from VCDS and something like this:

https://www.ecstuning.com/b-schwaben...868sch01b~scf/

I'm going through the function lists, and they use different terminology for some things so I'm having a hard time figuring out what the main differences are.

[jbritton]

Obdeleven is a mobile only product, its cheaper than vcds but I have to say vcds is better and has good support. Support is non-existent for obd11. As for the clutch job, it can be done on the jacks, however even if you can doesn't mean you should. Paying 10 hrs labor seems like a bargain to me for this job. Granted, mt is a bit lighter and less bulkier than dsg but it is huge and heavy, too.
P.S. going back to logging, what exactly needs to be logged? I keep my fingers crossed it's a spark plug issue but I honestly expect the worst case scenario which isn't too bad since it will allow me to go DP without worries. I'm just concerned how to pass CA visual smog inspection with O2 sensor spacers.

Got it, so VCDS > OBD11. I'm mostly just curious as something mobile or with a built-in computer thing would be handier as I don't always have a laptop with me.

For the clutch, I was thinking about doing it on my own because 1) I like doing that kinda stuff and 2) price. I'm just going off the dealer quote which was like $5k, but I haven't shopped around yet to see if there are any good shops near me that'll do it cheaper. It looks like a huge pain in the ass though so I wouldn't be opposed to paying a shop.

[Chris@EPL]

Pay the money and get the VCDS, it can do so much more and actually log the car and see what is going on. And when and if you want to sell it they still go for $150-175 with only 2 VINs left.

[jbritton]

Pay the money and get the VCDS, it can do so much more and actually log the car and see what is going on. And when and if you want to sell it they still go for $150-175 with only 2 VINs left.

I'm assuming it can be used to add tunes and do other programming stuff also? (Besides the basic resets and lights controls obviously. I've tried understanding what's on their feature list but some of it doesn't make sense to me.)

[hardfive]

I'm assuming it can be used to add tunes and do other programming stuff also? (Besides the basic resets and lights controls obviously. I've tried understanding what's on their feature list but some of it doesn't make sense to me.)

Itsa diagnostic tool. It can activate features that Audi didnt put in North American cars (needle sweeps, video in motion, secret menu), data log systems for troubleshooting, and can read error codes. In my opinion its part of the cost in owning an Audi as it can tell you where to focus your attention. You can run tests on systems to make sure their working properly. Its a much more capable-then-your-average OBDII reader. If you rely on someone else to read your error codes at a cost, you should sell your call now. My audi dealer is 173/hr and they dont read codes for free. There great cars but finicky for sure.

Its not a cable to flash tunes.

[jbritton]

Itsa diagnostic tool. It can activate features that Audi didnt put in North American cars (needle sweeps, video in motion, secret menu), data log systems for troubleshooting, and can read error codes. In my opinion its part of the cost in owning an Audi as it can tell you where to focus your attention. You can run tests on systems to make sure their working properly. Its a much more capable-then-your-average OBDII reader. If you rely on someone else to read your error codes at a cost, you should sell your call now. My audi dealer is 173/hr and they dont read codes for free. There great cars but finicky for sure.

Its not a cable to flash tunes.

Cool, thanks for the info. So basically the most advanced diagnostic tool you can get, plus the ability to change some things, just not do tunes. Guess I'll be ordering one today.

[fastboatster]

Itsa diagnostic tool. It can activate features that Audi didnt put in North American cars (needle sweeps, video in motion, secret menu), data log systems for troubleshooting, and can read error codes. In my opinion its part of the cost in owning an Audi as it can tell you where to focus your attention. You can run tests on systems to make sure their working properly. Its a much more capable-then-your-average OBDII reader. If you rely on someone else to read your error codes at a cost, you should sell your call now. My audi dealer is 173/hr and they dont read codes for free. There great cars but finicky for sure.

Its not a cable to flash tunes.

let's not spend any more time on convincing people to get at least obd11 or vcds to do the diag or how great (highly debatable) but finicky (100% true) this cars are. I have a more practical question - what do we need to log to understand this is a cat failure? I just want this POS fixed and tossed to over to the next happy owner.

[djn876]

Check O2 sensor voltages and see if any are slow to respond.

[fastboatster]

My quick update - not sure if I mentioned I had a broken crankcase vent hose. Somebody broke it and fixed it be sliding broken ends over a piece of rubber hose. Well, that repair came apart when I did the oil filter housing gasket. I replaced that hose yesterday, replaced spark plug #6 and I think I fixed this. I tried stabbing the throttle at 2k rpm - that’s where I had problems and hesitation when applying throttle quickly, I also did WOT acceleration on the on ramp up to 5500rpm, the car accelerated very cleanly and without hiccups. Actually liked how it drove yesterday, it hasn’t been this good for a long time. Perhaps that repair allow the air in for some time know.