Open catless downpipes running terrible

[rhanson713]

Just gutted my downpipes and decided going for a spirited drive without connecting them to the rest of my exhaust, they end about a foot after the flex-pipe. Let the car warm up and it has no power and runs rough from idle to about 2000rpms. After 2000 you can feel a decent amount of power but still runs very choppy. Hopefully all I have to do is weld the rest of the exhaust back up and this should cure the issue. Anyone run into this problem or should I be worried.

Stage 1 APR chip if it matters.

Thanks in advance


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[MacDaddy]

Did you put a spacer on the rear o2?

[rhanson713]

Yes. But the rear O2 shouldn't be reading anything other than catalyst output, right?


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[MacDaddy]

So i was told be a tuner it needs them for fueling. Id keep looking or scan for codes, im also apr stage 1 with no cats and it runs fine.

[rhanson713]

It's just gutted downpipes ending underneath the front seats now, nothing else


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[ADCS]

Open downpipes will not make your car run poorly.

What else did you disconnect when gutting them? I would start there.

[ADCS]

So i was told be a tuner it needs them for fueling. Id keep looking or scan for codes, im also apr stage 1 with no cats and it runs fine.

Primary O2, pre-cat (B1S1 and B2S1) gives fuel corrections. Secondary O2, post-cat (B1S2 and B2S2) gives catalyst efficiency feedback only.

[audacity]

have no cats at all for like 6 years car never ran bad. you must have by mistake disconnected something up top would be my guess when you were taking the cats off. theres a good bit of stuff you should take off to get access to the upper turbo nuts. check your work sounds like some type of vacuum leak or a sensor you left unplugged. no exhaust should not affect it

[vavJETTAw36]

Primary O2, pre-cat (B1S1 and B2S1) gives fuel corrections. Secondary O2, post-cat (B1S2 and B2S2) gives catalyst efficiency feedback only.

Wroooooooong. Rears have some say so in fuel control.


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[ADCS]

Wroooooooong. Rears have some say so in fuel control.


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Unless ME7.1 is different than 7.5....no they don't.

edit: and my 2.7 has 7.1.1

[vavJETTAw36]

I don't know if they are different. But I know rear oxygen sensors in our cars have some say so in fuel correction. Do you have a Bentley? Flip it to oxygen sensor section.


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[LINDW4LL]

OP, your car should not be running poorly with open DPs, even without the rear o2s. Something is wrong. My engine ran perfectly even with open DPs.

Secondary O2, post-cat gives catalyst efficiency feedback only.

I believe this is a common myth on here. Per Daz (RIP) - "You can't just "ignore" rear o2 codes. The rear o2's are taken into account in fueling as well."

[vavJETTAw36]

OP, your car should not be running poorly with open DPs, even without the rear o2s. Something is wrong.



This is a common myth on here. Per Daz (RIP) - "You can't just "ignore" rear o2 codes. The rear o2's are taken into account in fueling as well."

Yep. And per philadot, who is also an me7 guru http://nefariousmotorsports.com/foru...hp?topic=524.0


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[julex]

I can see how it can run poorly when tune is for a certain typical wastegate behavior and you just threw all that overboard by leaving open DPs. I bet that you have positive boost deviation code in there since now the turbos boost up much faster and thus you're capped at couple psi of boost and why you see choppiness when ECUs cuts the boost out on overboost..

[audis4noob]

I'm having the same problem after installing a twin 1

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