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Disconnecting the o2 sensor


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Hi all, I have not looked yet (rain)but I am fairly sure I have a large air leak in the exhaust manifold/gaskets which is causing the S4 to run very rich and I am reluctant to drive it and damage the catalytic converter. I have done my best to solve this problem from other sources,( except the  ecu) as I have long suspected a minor leak.

 I need to drive it about 20 miles to a friend’s  garage and engine crane, engine out new exhaust.My question is, will my S4 drive ,without problems ,with the o2 sensor disconnected on default ‘open loop’ settings so the large amount of excess fuel does not destroy the cat.   Have you done this?   Thanks for any help.

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If you disconnect the O2 sensor, the car will indeed revert to open loop. Which should be OK-ish, certainly not rich enough to damage the cat. Even with the O2 connected, the ECU will run rich under acceleration, but never excessively (unless something is wrong).

I have made many mistakes in my life. Buying a multiple Lotus is not one of them.


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Hi thanks for replies, the cat is about 5 years old from SJ , I removed and kept the original simply because of its age.The over fuelling is now very bad. I am toying with the idea of putting air up the tailpipe to try to identify where the leaks are and how bad they are to plug them with gun gum as a temporary fix to drive the 20 miles or as I said to disconnect the o2 sensor or both.Will a hair dryer work?Will a vacuum cleaner in reverse work or else I will get under the S4 when the engine is running when cold.None of these remedies has appeal in the wind and rain! Has anyone tried reverse air up tailpipe? I repeat, I have done all the likely sources of running rich except ecu.

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Hi Steve,

Usually a leaking exhaust manifold gasket is visually evident with sooty marks and the like.

Can you not hear a leak while running? usually quite noisy!

I'm thinking you may be on the wrong scent here.

Your hoover (in reverse) method is unusual but might work with rags stuffed in the throttle body inlets and spraying soapy water on the exhaust manifold. Doubt a hair dryer would be any good.

What other "likely sources" for rich running have you checked?

What leads you to think it is actually running rich?



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