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Exhaust leak and DTC P0420

stealthee

stealthee

New member
I had a very minor exhaust leak when I purchased my 07 GT in March. It has progressively gotten worse and is now at the point I need to do something about it. I just need to get under the car and find out where exactly it is leaking from.

Today, though, on my way to work I noticed the Check Engine Light came on. Car didn't run any differently and all gauges remained normal. Instantly I thought it had something to do with the exhaust leak and an o2 sensor. I stopped at Advance on my way home from work and borrowed the scan tool. It gave me P0420 Catalyst System Effeciency Below Bank 1.

Would you agree with me that this CEL is related to my exhaust leak, or is it just a coincidence? Any other input on my current situaion? Thanks in advance.
 


Most likely.

Thanks for pulling that code...I'm lazy and don't want to search. Is the leak at the rear manifold or before the front o2?

I had that code once...right after I removed my converter...
 
It sounds like its at the manifold. Almost like where the manifold meets the downpipe. I'm going to stop at my friends shop tomorrow and throw it up on the lift to check it for sure. Once I know for sure I will get the gasket and change it out.

I did reset the code while I was at Advance, it stayed off for about 10 miles then came back on though.
 
Got an aftermarket DP going on it or are you leaving it stock?

JW...as there are tons of people tossing up 3" catted and non-catted DP's FS recently. Also expect a gain back in MPG's...I noticed a little difference after I got all of my leaks sealed up.
 
Its stock. I have noticed my MPG's getting worse and attributed it to the exhaust leak. Thanks for the reassurance I am on the right track. Now I just need to get off work on time and get the thing back to how it should be.
 


Yeah. I know it. I have had everything I need to make a custom intake since March, and all the parts and pieces are still sitting on the floor behind my drivers seat. LOL Things should be slowing down with work, so hopefully both cars can get some loving here soon.
 
I just moved and put PLENTY of things on the back burner...trust me...hence my recent plug change...AL103R's with almost 14k miles on them :D
 
Ok, so I found my exhaust leak.

leak.jpg


If I bought this down pipe here or something like it, that should fix me up correct?

Hogan Performance W-Body 3" Stainless Steel Downpipe: 3800 Performance

I feel like I am asking a stupid question but I am so used to my Stealth and the exhaust routing on it that I want to make sure I order the right part.
 


Exactly. So looks like I am gonna get a new downpipe. I may as well get the whole thing and I can just bolt it in myself and be done.
 


Stealth...that specific DP you posted is a shorty...which is only 3" down to the converter...not a bolt-in unit...it needs welded.

ZZP sells shorty's for $89.99 if that is what your going for. Are you keeping the cat? If not...I'd just get a bolt-in catless DP from ZZP...it's $139.99
 
I forgot to update this post. I did purchase the bolt in catted dp from ZZP. I should have it Tuesday.

I honestly hadn't looked hard at the exhaust prior to posting this thread. I did not realize the stock cat was in the place where the shorty would go.

Hopefully all goes well on the install. I'd be happy if my MPG's went to around 23. It sucks to go from 25-26 mpg with a 20 gallon tank in the Stealth, to 20 mpg with a 17 gallon tank in the GP.
 
FWIW, I see upwards of 28+ in the blue car...and it's far from stock. Custom tuning for your car and looking into lean burn tuning would net you some awesome MPG's.
 
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