Stumbling or misfire under load in Fourth Gear

[aj6]

I have a 2015 A3 2.0 with 23,000 miles. Current powertrain/exhaust additions are APR Stage 2 ECU and DSG tunes, and a BB turboback exhaust.

A couple of months ago, after installing the downpipe/exhaust and going from Stage 1 to Stage 2, I noticed that heavier throttle acceleration in fourth gear was causing a rumbling from the engine from 2200-2800 rpm. No surging, just a rapid rumbling and noticeably slower, hesitant acceleration. This does not occur in dynamic/sport/M mode, only normal drive. No CEL.

I had the DSG tune flashed in hopes that it would remedy this, as the car is my daily driver and lower rpm fourth gear seems to be a staple of my commute. The intensity of the vibration has decreased somewhat, but it is still present and in the same form and duration. Does anyone else have this issue? I'm thinking about investigating spark plugs / carbon buildup, but on a car this new I hesitate to believe those could be the culprit.

[Workflow]

Regular drive mode is a bitch when tuned especially at that RPM. I find that DSG tunes are helpful in keeping the car from racing to 6th, but I certainly stay out of D mode unless it's highway driving. Doesn't sound like a misfire, but get yourself a little OBD scanner and connect to Tourque app (or equivalent) if you don't have a VAGCOM cable. Pretty helpful tool in pinning down a misfire and other errors, etc.

My advice is to simply have the shop that tuned you have a look and run proper logs.

[markn1689]

APR tuned, huh?

apr has a LONG history of failures. i blew TWO SETS of turbos in my old stage 2+ b5 s4 (luckily i reverted to stock and had it covered under warranty)
they rush software, cut corners, don't test fully. and they just plain don't care
i will never install ANYTHING APR on my car. its junk

[aj6]

Thanks for the insight Workflow. I'll do what I can with my OBD tool, then on to more diagnostics if I don't run across a solution.

markn1689, sorry you had a bad time. My APR equipment and software is remarkable and I've been pleased with the company overall. Edit: I've noticed you trolling over in another thread. Take a break and go running and work that anger out of your system.

[HurrayFive]

It sounds like the clutch pack is slipping. I'm also Stage 2 w/ their DSG software and the same downpipe, if I'm cruising (not from a stop) I never go past half throttle unless I'm over 3K RPM. You can definitely feel clutch slip below 3K if you dig deep into the throttle in 4th gear or higher. It's just way more torque than the stock Haldex unit is rated for. Has been the case in most of my high output tuned 2.0T cars. Just drop a gear when you need more than light throttle when cruising at that RPM and I bet it goes away.

[aj6]

Edit: it shouldn't be simple clutch slip. These guys are running much higher torque than we are on the same stock unit. http://forums.vwvortex.com/showthrea...clutch-upgrade

Original...

Great answer, thanks. This is my first tuned car, so I'm unfamiliar with clutch slip. I thought it needed to be accompanied by engine surge, but I suppose the TCU is limiting output when it senses a slip?

I do wish the TCU programming was more aggressive about downshifting in drive mode. Hopefully if that is indeed the issue we can see improvements in a future update.



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[markn1689]

Thanks for the insight Workflow. I'll do what I can with my OBD tool, then on to more diagnostics if I don't run across a solution.

markn1689, sorry you had a bad time. My APR equipment and software is remarkable and I've been pleased with the company overall. Edit: I've noticed you trolling over in another thread. Take a break and go running and work that anger out of your system.

i'm not mad. my car doesn't stumble or misfire. just trying to inform people about greedy tuners that could care less when their tune damages your car. enjoy your apr tune and the misfires that come with it

[HurrayFive]

Edit: it shouldn't be simple clutch slip. These guys are running much higher torque than we are on the same stock unit. http://forums.vwvortex.com/showthrea...clutch-upgrade

Original...

Great answer, thanks. This is my first tuned car, so I'm unfamiliar with clutch slip. I thought it needed to be accompanied by engine surge, but I suppose the TCU is limiting output when it senses a slip?

I do wish the TCU programming was more aggressive about downshifting in drive mode. Hopefully if that is indeed the issue we can see improvements in a future update.



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Peak power and torque is never the problem, these little DSG's have been proven to hold serious power, it's how you're using it. I don't care what software you're running, forcing 350+ lb/tq below 3K RPM is always going to lead to slippage in higher gears. There's a reason even the S3 is capped at 280lb/ft stock. That doesn't mean you can't run waaay more power than that but you have to drive accordingly.

I'm also not sure which is slipping, it could be the Haldex clutch pack that has a hard time, which has nothing to do with the DSG clutches. Long story short, the fact that you're only experiencing it under load while cruising in a higher gear at that RPM is a dead ringer for slip. You can verify it's slip by dropping a gear and getting on the gas in a ratio which lets the clutch pack actually grab and go. Engine problems, IE, spark plugs, coils, PCV recirc related, would be more likely to persist throughout the rev range. It still sounds like slip.

[aj6]

I'm convinced. I'm not opposed to eventually upgrading clutch packs, as long as I can isolate the issue for certain.


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