Exhaust Plumbing and Sensors

[chucktoo]

I think I now understand the new plumbing ? Maybe ?

 

1: Front O2 sensor at exit RH cylinder bank in manifold

2: Pre Cat in uppie pipe

3: Temperature sensor in uppie pipe for cat protection

4: Turbo

5: Down pipe with Front Cat

6: Rear O2 sensor just before Rear Cat in Rear Cat Pipe

7: Rear Cat - this is clearly not measured

8: Resonator Chamber

9: Dual exhaust mufflers

 

So if I have the right the first O2 sensor does the rear F/A ratio adjustments.

 

The Temperature sensor is really not needed if no cat but is a place to mesure realative exhaust temperatures.

 

The cat in the down pipe is the one that really gets measured so if deleted you need fake the O2 in the rear cat pipe.

 

The rear cat may clean up the air but other than looking for it there is no way to know it is working.

 

Everything after the rear cat is just noise control.

 

If I have it right faking the rear O2 sensor means you can have no cats ?

 

http://www.overboost.com/story.asp?id=1205

 

Charlie

[KGreb]

You've pretty much got it right by my understanding. Most if not all of the A/F correction is done by the front O2 sensor. The rear O2 is used to determine that the catalytic converter is functioning. The EGT is just there to determine if the up-pipe cat is about to fall apart from high temps. Many folks use a CEL defeat on the rear O2 due to CELs from having changed out the main cat. This could be needed if a high flow cat is used, not just when running without any cats. Most of the high flow catted downpipes for the WRX will trigger a CEL under certain running conditions (ie cold temps, sustained 55mph cruise, etc).

[BoxerGT2.5]

[quote name='KGreb']You've pretty much got it right by my understanding. Most if not all of the A/F correction is done by the front O2 sensor. The rear O2 is used to determine that the catalytic converter is functioning. The EGT is just there to determine if the up-pipe cat is about to fall apart from high temps. Many folks use a CEL defeat on the rear O2 due to CELs from having changed out the main cat. This could be needed if a high flow cat is used, not just when running without any cats. Most of the high flow catted downpipes for the WRX will trigger a CEL under certain running conditions (ie cold temps, sustained 55mph cruise, etc).[/QUOTE] I have the TurboXS high flow cat and have yet to get a CEL.

[KGreb]

[quote name='BoxerGT2.5']I have the TurboXS high flow cat and have yet to get a CEL.[/QUOTE] I had the same system. Try driving 15 miles with the cruise control at 55mph and let me know if you're still CEL free. I didn't have a CEL for almost a year until it popped up under those driving conditions. It was 100% repeatable. The cat just doesn't stay warmed up enough to function properly under certain conditions. That's why the stock exhaust has the primary cat so close to the turbo, where temps are higher.