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surging after putting a new exhaust on

secretive

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Hi guys, I know nothing about cars but i know i like how they sound :) My muffler shat itself so i decided to put a new exhaust on 2.5" catback on it yesterday and since getting it on the car is aurging when i am coasting, it's fine when it idles and under acceleration it only happens when i'm at speed and take my foot off the accelerator and coast, i took it back to the exhaust joint and the guy said it just needs time for the computer to recognise the greater airflow as its no longer choking does this sound right or is he pulling my leg? All help greatly appreciated Thanks, oh btw its a vx v6 supercharged...don't know if that makes a difference....
 

acarmody

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Yeah hes pulling your leg. Check all the hoses and connections in or near where you worked.
 

K Lewy

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You need to reset the ECU.
Once you have installed an exhaust system, it doesnt automatically change. Contact Tenneco (Walker/Lukey) exhaust. Or go to like Autobarn or Supercheap Auto and they will have a lukey exhaust catalouge, and there is TECH TIPS. It explains how to reset ECU once you have fitted an exhaust.
 

Decicrate

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You will find it is the deceleration mode. When you take your foot off the accelerator it is the ECU's way of keeping the engine running when there is no throttle being applied and saving fuel and emissions at the same time. Your car has done this since day 1, but you have only noticed it because it is now audible with the louder exhaust.
With our L67 VX, you can actually watch this when I have the real time computer plugged in.
I can get to 100KPH and lift off the throttle, the revs will drop to about 1100RPM and then fluctuate by a couple hundred rpm. I can see it on the gauge screen (real time system) but can only just see a fraction of movement on the dash tachometer. We currently have a stock exhaust, so I can't hear it happening in the car.
 

Decicrate

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Did you put the O2 sensor back in and connect it?
Its 2 x O2 sensors on the VX and there should be no reason to remove them when doing a cat back system.
One would also think that if it were left out you would be able to hear it straight away.
 

Not_An_Abba_Fan

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The VX PCM doesn't need to be reset. They don't learn or relearn anything, they compensate. When reset it only goes back to factory defaults and then starts compensating all over again.

Resetting earlier PCMS resets the TPS too, this can cause rough running and erratic idle, but not on the VX.
 

secretive

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I have no idea what was done to it because it got done by my local exhaust place i dropped it off worked fine picked it up drove it and it done this, i figured they should have to fix the problem seen as it didn't happen before it went in but they keep saying that the computer just needs time to relearn the new flow from the exhaust....sounds weird to me thats why i thought i'd ask on here coz u guys seem pretty clued up :)
 

soop

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Its 2 x O2 sensors on the VX and there should be no reason to remove them when doing a cat back system.
One would also think that if it were left out you would be able to hear it straight away.
I didn't realise the 6cyl's had two as well, my bad.

If he didn't clip one in properly, it'll drive like a dog and not necisarily throw a code. (Learned that the hardway too lol)
 

Not_An_Abba_Fan

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i figured they should have to fix the problem seen as it didn't happen before it went in but they keep saying that the computer just needs time to relearn the new flow from the exhaust....sounds weird to me thats why i thought i'd ask on here coz u guys seem pretty clued up :)
Changing something on a car from standard to something else will usually make the car behave differently. It's not necessarily a fault, just different. Just because you have never felt this before doesn't mean it wasn't doing it, it just wasn't noticeable. Now it is.
 
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