# EPC light after installing turbo back??



## hybridcmk (Oct 10, 2013)

OK so I installed a milltek turbo back exhaust, no cat and non resonated with no valves. 
Was wondering if anyone else has ran into this problem?
It only happens WOT at the end of 3rd gear going into 4th then the EPC light comes on and puts me into limp mode.
The rear valve harness/clips aren't plugged into anything so im not sure if that's the problem or if the car is still trying to compensate for the different air/fuel mixtures.
Thanks for any advise


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## rabbitgtibbar (Apr 29, 2002)

You took the cats out of your car, made no attempt to resolve that, and you can't figure out why that pissed the car off? :screwy:


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## sevenVT (Aug 18, 2004)

hybridcmk said:


> OK so I installed a milltek turbo back exhaust, no cat and non resonated with no valves.
> Was wondering if anyone else has ran into this problem?
> It only happens WOT at the end of 3rd gear going into 4th then the EPC light comes on and puts me into limp mode.
> The rear valve harness/clips aren't plugged into anything so im not sure if that's the problem or if the car is still trying to compensate for the different air/fuel mixtures.
> Thanks for any advise



Your car doesn't compensate for emissions faults, it codes to tell people that your emissions system is broken or not behaving as intended at the very least.

If there are built-in places for the sensors to be reinstalled in your new system, use them and hope that the system was designed well enough to trick your car into thinking there's emission control between the sensor and the ECU. 

Otherwise the code is appropriate, you are spitting out emissions that your car does not expect, be it clean air if the sensor is freeballing, or much "dirtier" air as you removed an expected piece of hardware between you and the O2 sensor that would be placed post-cat.

Also if you are in a state that expects those emission control pieces... expect to fail inspection.


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## hybridcmk (Oct 10, 2013)

i get the whole dirty air and emissions part. I have a bung spacer that im going to try and see if i can trick the system to think that theirs a "cat" still there. if that doesn't work, i eventually plan on chipping the car and then the problem


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## Ricky11 (Jun 7, 2012)

This is interesting because I have the resonated Milltek turboback but with a high-flow CAT and have absolutely no problems. 

I also have the non-resonated piping which I also tested and never had any issues but I also has the high-flow CAT. 

I did however have the light go off and enter a complete engine cut off when running a preliminary stage 2 tune. But when it occurred, it was exactly the same situation - from 3rd to 4th. Since it was pretty consistent, we went back to a refined stage 1 - which made it to away immediately. 

I can only imagine how raw your S3 sounds...


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## hybridcmk (Oct 10, 2013)

Ricky11 said:


> This is interesting because I have the resonated Milltek turboback but with a high-flow CAT and have absolutely no problems.
> 
> I also have the non-resonated piping which I also tested and never had any issues but I also has the high-flow CAT.
> 
> ...


its alittle raspy but its loud, like really loud haha. but at idle or cruising speeds its barely notifiable which is awesome.


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## kjcooperncsu (Jan 5, 2015)

What was the code that caused the fault?


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## hybridcmk (Oct 10, 2013)

kjcooperncsu said:


> What was the code that caused the fault?


i havent scanned it yet. im going to scan it at work this week. if i do a key cycle it goes away and the car drives fine again. pretty sure its just the car freaking out that theres not cat


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## kjcooperncsu (Jan 5, 2015)

the reason I ask is it sounds very similar to a problem that some tuned stage 2 gti guys are having. Your car should not go into limp mode because of a catless downpipe giving a degraded cat signal. I'm wondering if u are pulling an overboost code like they are


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## sevenVT (Aug 18, 2004)

Ricky11 said:


> This is interesting because I have the resonated Milltek turboback but with a high-flow CAT and have absolutely no problems.
> 
> I also have the non-resonated piping which I also tested and never had any issues but I also has the high-flow CAT.


I've had similar experience where a high-flow seems to be within threshold of the OEM programming for EPC at least.


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## hybridcmk (Oct 10, 2013)

ok so i went and got the unitronics satge 1.5. 
the car no longer throws the epc light. 
car is a completely different animal. 
deff recommend getting the s3 tuned.


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## araemo (Dec 9, 2012)

hybridcmk said:


> ok so i went and got the unitronics satge 1.5.
> the car no longer throws the epc light.
> car is a completely different animal.
> deff recommend getting the s3 tuned.


Why not stage 2 if you already have the downpipe?


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## hybridcmk (Oct 10, 2013)

araemo said:


> Why not stage 2 if you already have the downpipe?


there is only one tune from unitronic right now for the s3


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## araemo (Dec 9, 2012)

hybridcmk said:


> there is only one tune from unitronic right now for the s3


Their website lists 1, 1.5, and 2 as 'under development'...


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## hybridcmk (Oct 10, 2013)

araemo said:


> Their website lists 1, 1.5, and 2 as 'under development'...


exatly, stage 1 is released to the public but there website isnt updated yet. 
stage 2 is in development because it isnt availbe yet.


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