So I've had the GMPP Performance exhaust installed on my car for about 3 years now & just a couple of days ago I've noticed a slight hissing noise under acceleration. When I'm in my car, it sounds like it's coming from the down pipe area or closer to the engine.

I dropped my car off at the dealership, they called me back & said they didn't notice anything & couldn't find a leak anywhere. I told the service advisor that I normally deal with that it has to be a leak & he said he will take it out for a drive himself to see if he notices anything..... like wtf.

I know for a FACT there's a leak & now I don't know what to do? Could my exhaust be toast, should I take it to a muffler shop...?

 

do u have a stock DP?

 

Yes.

 

cat might have blown apart and isnt "complete" anymore....so u have that whistling sound coming from inside the cat....its a possibilty and a DP is a worthy upgrade anyway so that would be first on my list.....also check where your pipes intersect.... i have the borla exhaust (borla designed the GMPP) and that is the only other place i can think of where ud be getting a leak

 

Thanks for the info. I'll take note of that.

 

just realized that you are up in canada.....if you DD your car, the header and dp might have some tiny holes from corrosion due to the salt and winter.....catback is fine cuz its stainless...

 

The downpipe is stainless to.

The exhaust "manifold" is cast iron, and have been known to crack over time.

 

i stand corrected i forgot its stainless, but i think we can both agree its not of the highest quality

 

The flex pipe on the stock DP is notorious for failing.

 

So it could either be the Cat, or the headers? Yes, I do drive it all year round.

 

It's likely grade 409 stainless.

This.

I'm willing to bet the flex coupler took a dump on ya.

 

1. cat could have failed

2. flexpipe in DP could have failed

3. your header may be cracked as its cast and can fail especially since you see a lot of winter

4. the interlocking on your catback where the pipes connect into each other.....this prob is not the case but worth a check anyway

 

Is there any way to check? I don't have a lift or really any garage space to check. My car is still at the dealership. I might as well get them to check for me if it's possible...

 

four things

a) stock gm downpipes SUCK. its 90% at the flange.flexpipe section

b) gm probly wont fix it for free because they need a new whole cat/downpipe, but also because now you have an 'aftermarket' exhaust, even though its gm

c) good luck finding a stock dp for under $300, i've been looking forever

d)dont get zzp, i went that route and my exhaust sounds like **** now

 

I was thinking of going ZZP 2.5" downpipe & BadMab header after all of this.... What's so wrong with the ZZP downpipe?

 

Most likely the flex part on your header is going bad or the gasket between your header and dp.

 

:+1 on the flex. GM wouldnt fix mine.
They said the cat is covered under emission warantee but the flex pipe isnt covered ??? Argued with them in the service dept for a while but they wouldnt budge. I asked them how I was supposed to fix it since they dont sell the flex seperately and they said I would have to buy a whole new DP. I told them to shove it and got a new flex from Powell and had it welded in

 

Yes.

You can visually inspect it from the top. Have the car idling, and look/listen for any signs of exhaust gas leaking. If the leak is bad enough you will see the crack in the flex right off the bat.

Also, look for a leak at the 2-bolt connection flange that connects the downpipe to the catback. The 2-bolt flange is notorious for leaking, and you may just need a new gasket.

I never had one problem with my stock downpipe, and I may sell it after I install my ZZP downpipe. I'll let you know if you are still looking for a stocker at that time.

 

i got zzp catted 2.5, badmab and corsa catback. it sounded magnificent before the downpipe, nice, deep and mellow, no rasp.

put on the zzp dp and now it sounds ok at idle and low rpms, but once u get on it at all... nothing but rice shaking in a folgiers can dude. its terrible. but... if you wanna new dp, but mine!! seriously

 

I'd rather hear that then a hissing noise coming from an exhaust leak. LOL
As long as the zzp downpipe is good, I'm going with it. Id rather not spend any more money then I'm looking to spend.

 

Well I just got off the phone with the service advisor & told him all the things that could be wrong with it(Thanks to you guys in this thread). He still wants to go out for a spin in it himself(I have no clue why) to see if he hears anything himself(which he probably won't notice because he doesn't drive it all year round).

If no one can still find a leak or problem with my car I'm just going to buy a new downpipe from ZZP and a BadMab header.


Does anyone know the approximate installation time/cost for either of those two things & will they bolt up fine to the GMPP performance exhaust?

 

Update: Just got off the phone with the service advisor & he admitted he DID hear the same hissing noise & is bringing it back in to the service garage. So, off to waiting again... I'll let you guys know what ends up happening.

 

sounds good as far as the header/dp i recommend zzp long tube header and dp u have the option to go catted or catless.....going to be bout 500ish though

 

I don't want to go catless. But I was also considering that combo.

 

Update: Just got a call back & there's a hole in the Flexpipe/downpipe(looks like i bottomed it out on something they said). They have the part in stock & I got quoted 685$ for the part + Installation. I told him to go ahead & install it.

I wish I could have waited & bought an aftermarket downpipe & saved some money but It's bad enough as it is & I don't want to wait any longer... I'm just glad my car is payed off In a week. I guess that's why they call it the "Stealership".