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Old 05-09-2013, 01:24 PM   #1
scoobyman83
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Default Exhaust leaks and high EGT

For the second time i notice something weird -

I have an exhaust gas temperature probe in my downpipe, 1 inch after the turbo (for safety reasons) and after fixing a crack in my up-pipe in january i realized that my EGT's were now 50-100 degrees C lower than usual, which was pretty nice.

Last week i noticed that my EGT's are higher than usual and today i had the time to look around and lo and behold, i found a new crack in my up-pipe.

Is this a known condition ? Could anyone please explain to me how a crack in exhaust piping can affect EGT's as i fail to see a connection
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Old 05-09-2013, 01:38 PM   #2
RaceFaceXC
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You are asking how a crack in the exhaust would affect the temp of the gas inside it? How would it not?
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Old 05-09-2013, 02:09 PM   #3
scoobyman83
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Originally Posted by RaceFaceXC View Post
You are asking how a crack in the exhaust would affect the temp of the gas inside it? How would it not?
Well yeah, i guess your question is as solid as mine, an answer to either questions would be fine.
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Old 05-09-2013, 05:48 PM   #4
Frank_Zuccarini
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Sorry that I don't have an answer for you, but I would think that any leak anywhere in the exhaust system would let exhaust gases out, rather than ambient air in.

A HUGE leak could conceivably reduce back pressure. Could that result in an increase in EGT? A freer flowing system?

Frank
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Old 05-09-2013, 06:10 PM   #5
RaceFaceXC
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The pressure inside the exhaust fluctuates rapidly as valves open and close. Any un burned gas may ignite after fresh outside air supplies the needed oxygen to support combustion? Is Turbo exhaust pre turbine always positive pressure relative to atmosphere?
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Old 05-10-2013, 06:36 PM   #6
ProfessWRX
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Quote:
Originally Posted by scoobyman83 View Post
For the second time i notice something weird -

I have an exhaust gas temperature probe in my downpipe, 1 inch after the turbo (for safety reasons) and after fixing a crack in my up-pipe in january i realized that my EGT's were now 50-100 degrees C lower than usual, which was pretty nice.

Last week i noticed that my EGT's are higher than usual and today i had the time to look around and lo and behold, i found a new crack in my up-pipe.

Is this a known condition ? Could anyone please explain to me how a crack in exhaust piping can affect EGT's as i fail to see a connection
You are creating a turbulent area where the leak is with nonlinear flow. Turbulence will raise the temp due to the flow limiting.

Then there's also the effected timing advance change sometimes due to the pcm reading false knock.

Then depending on where the leak is the afr will be calculated wrong if the o2 reading is post leak.

So, your egts can raise from potential change in flow, change in timing, change in afr.

Last edited by ProfessWRX; 05-10-2013 at 06:45 PM.
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