# Exhaust Leak at manifold to catalytic converter connection, how bad is this?



## ooobombz (Aug 15, 2005)

I bought a 1997 Golf GTI 2.0 last year because I just needed some cheap wheels. The gas mileage has never been great, but since I don't drive that much I didn't really care. It feels like it's running fine, but obviously 20-21mpg no matter how you drive it isn't going to cut it.

I decided to look for an exhaust leak.

I learned 2 things:
1) I have some form of aftermarket tubular exhaust headers (I'm thinking eBay or OBX)
2) I have a leak nearly 1-2 inches behind the O2 sensor in the connection from the exhaust header to the catalytic converter. I'm guessing it just some bad fitment with the donut seal right there.

How bad is this? It feel like someone gently blowing out (quite soft, but definitely more than a 'pinhole'). Could this be the culprit even though it's behind the O2 sensor? (Only behind by 2 inches tops)

Let me know what you think. I'm planning on fixing the leak and perhaps swapping out what sensors I can (O2, maybe the coolant temp sensor per http://javalins.wordpress.com/vw-golf-mk3/troubleshooting-common-fixes/ page).

New air filter, oil, oil filter, distributor cap, plugs, pug wires. I wonder if maybe I should get an ECU that's flashed for this 'after-market headers / loud glasspack muffler' combo it's sporting in addition to the K&N on the intake.

-D


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## OddJobb (Nov 6, 2004)

Yes, this may be part of the reason your gas mileage is lower. The O2 sensor won't read correctly if some of the exhaust is escaping before it can read it, possibly causing it to run rich. There's also a flat triangular metal gasket that should be between the header and catalytic converter. It may be missing and causing the leak. You cannot flash the ECU in this car, and if you could it would have not anything to do with the exhaust. The ECU has no clue what kind of exhaust would be on the car. Fix the exhaust leak and get new O2 sensors. I think you'd see an immediate improvement in you MPG with this alone.


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## ooobombz (Aug 15, 2005)

*thanks for the reply*

Thanks for the reply. Yeah, next weekend I'm going to take it apart and replace the sealing ring in that area. However, here's a pic to further explain what's going on if anyone wants to chime in, etc. You always need pics for the internet 



















I should've taken a photo when it was earlier in the day and it was on jacks, but this is just to show the location of it all, blah blah...

My only concern is that the leak may ultimately be of little concern because it's after the 02 sensor, which btw doesn't seem to be a cheap part (the sensor). That 02 sensor does look like the original so changing it may not be a bad idea regardless.

-D


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## OddJobb (Nov 6, 2004)

Dude, that's all f**ked up. That header did not fit correctly and the previous owner just rigged that crap up all wrong. You're going to need to get a header that fits correctly. You're not going to be able to fix that.


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## stoveyy (Aug 18, 2007)

yeah that ****s alll out of wack. you might be able to get some nuts and bolts and clamp down like no other and seal it up, but quite frankly its after the first o2 sensor. it wouldnt cause much of an issue fuel wise. 

hows your air filter? is it a stock intake or some jerry rigged garbage? plugs/wires/cap? look into the maf sensor, see how thats working. any vacuum leaks? any codes at all?


edit, i just re read and obviousy skipped some parts. the odd intake could cause issues. theres a vacuum line that goes from the intake manifold to the stock airbox. whats the plugged into? or is it just leaking away.


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## jorge r (Apr 27, 2006)

Can't tell if the 02 sensor wires are there. I'd replace the doughnut and use exhaust paste to help seal and hope it seals it. An exhaust leak causes air to enter the exhaust, the exhaust pulsates and siphones air into the exhaust pipe, emissions testing would cause wrong or bad readings.


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## ooobombz (Aug 15, 2005)

*just to be thorough...*

I present to you Exhibit A:










That's a sales photo of the OBX brand exhaust header for this car. Notice how the exhaust is not made to properly fit to the 3 bolt, metal plate type flange that the car's stock catalytic converter has. Instead it goes into a janky exhaust donut type seal which is then tensioned onto the catalytic converters flat, plate type gasket. Seriously OBX, wtf, two points of possible leakage instead of making it fit properly to start with? Really dumb, but not the previous owner's fault.

I'll be getting a new donut, cleaning everything up, covering all the sealing points with exhaust paste and tightening it down like a mofo. My Bentley manual has a little diagnostic I can do on the O2 sensor to see if it's faulty. I'm not getting any codes though (except aigbag, guessing clock spring) so it's probably okay. Still, might as well fix what needs fixing.

I'll post a follow-up as it happens. Thanks for the input guys.

-D


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## Turkish_Royal (May 29, 2018)

Was there ever an update to this? I am in the same boat with leaky flange and M going to try and tighten it down as best as possible hoping for the best


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## fastinradford (Aug 3, 2010)

Weld the flange onto the header. 

Doesn’t seem to complicated to fix.


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## zero. (Aug 14, 2001)

That's just a type of ball/socket spring bolt flex joint to prevent the header from cracking. If it's leaking, you can replace just that part or weld on an actual flex joint but there isn't much room for one. Possible just the bolts are loose too, but on similar Raceland headers I've remove, typically the donut flange seal deteriorates.


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