surging after putting a new exhaust on

[secretive]

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]

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

[K Lewy]

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.

[soop]

Did you put the O2 sensor back in and connect it?

[Decicrate]

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]

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]

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]

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]

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]

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.

[secretive]

but you can see it on the taco fluctuating before i put the new exhaust on the taco never fluctuated so wouldn't that be a sign that it's just started since putting the new exhaust on? Like i said i'm clueless when it comes to cars just know the basics like how to check my fluid levels

[Brett_jjj]

Mate,I think that exhaust place is full of it.But play their game and give it a few days,then if its no better,take it back to them and tell them you want it fixed..Ive never had a problem with a car running like crap because an aftermarket exhaust system was fitted.And Ive helped mates fit a few of them, and I have done a few myself.And what has happened to your car, has not happened to any that Ive done,so theres something not right there somewhere..And as for the computer,it will adjust itself pretty much straight away after the engine is started .The fuel trims might take a bit of time to work themselves out,but they wont cause it to hunt and run bad etc.Id say the exhaust place has probably knocked something off around the engine somewhere and they havent realised,like a vacuum hose at the rear of the engine or whatever.

[secretive]

thanks heaps everyone for your help and suggestions the more infor i can get the better prepared i can be in resolving this when i take it back to them and yeah they said give it 200k's to settle in then see how it is so far i've done 160k's and still doing it so doubt it will magically fix itself at 200k's but for now i'll play there game.

[delcowizzid]

a lot of holdens do this after exhausts fitted cuts in and out of decel mode some even jump from decel to acell mode after an exhaust when going downhill .others do it cause the o2 sensors arnt fast enough reacting

[brad_m_is]

its normal mate every commodore i have driven has done it as u coast down a hill at 100 kays u can see the tacho moving a small amount totally normal. its only u noticed it as u can now hear it!

[Tree cutter]

My Calais has always done it. After i fitted new spark plugs, fuel filter and air cleaner it doesnt surge as much.