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Would a leaky flex section in DP cause A/F's to be lean?

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Clutch450

10+ Year Contributor
252
1
Jan 15, 2009
Lancaster, Pennsylvania
Yesterday I noticed that my Wideband was reading extremely lean(17.5-18). It normal jumps around 14.7 while cruising. The car run perfectly fine though. No noticable loss in power. When I make boost the A/F's drop to around 11 like usual. But cruising they sit around 18. So today i jacked the car up looking for a problem, and noticed that the flex section in my DP is leaking. Since the flex section is before my WB O2 would this be causing my WB to be reading so lean?
 
I just replaced my front O2 sensor a month ago.
And last time I took a log with link the front o2 was cycling good.

The car is going to an exhaust shop next week for a cutout to be installed, while it's there I will just have them weld in a new flex section
 
You might see if they can't just eliminate the flex, I know they don't advertise it on their website but Buscher makes DP's that have no flex section because they're prone to leaking.

:dsm:
 
Wouldn't not having a flex section in the DP be a bad thing? Break/bend exhaust flanges and such. I though they were there for a reason
 
mine did the same thing when my flex was leaking... fixed the leak and my WBO reads accurately now
 
They are there for a reason but between your motormounts and your rubber exhaust hangers you should have enough play in the exhaust system to not break stuff. You can always move the WB o2 sensor forward of the flex section and not worry about your AFR's being off if you want to run the flex section.

:dsm:
 
Keep the flex section in your DP. Either get a new one if it's not fixable or weld the hole if it's able to be fixed. Best thing you can do is move your WB to BEFORE the flex section so you don't have to worry about this down the road.
 
ok, thanks everyone for replies. I'm going to get the flex pipe fixed because I hate the way it sounds with the leak and also get my WB moved to before the flex section
Thanks
 
They are there for a reason but between your motormounts and your rubber exhaust hangers you should have enough play in the exhaust system to not break stuff. You can always move the WB o2 sensor forward of the flex section and not worry about your AFR's being off if you want to run the flex section.

:dsm:

NO NO NO. Do not run without a flex pipe. The weight of the exhaust, turbo, mani will still be hangin off the head which is not good. The motor mounts and rubber hangers dont let the exhaust flex with the motor like the flex pipe.

To the OP I would move the o2 in front of the downpipe. Cheap and you eliminate an issue. But IMO the car should not run lean at cruise or WOT unless the leak is huge. Usually noticeable more at idle.
 
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