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2G O2 housing/Downpipe leak

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ohlegend

10+ Year Contributor
581
42
Apr 2, 2012
Pemberville, Ohio
The issue that I am having is when my car idles for a while (or drives) the engine will stay in open loop, and when it changes to closed, loop it either goes too lean or rich and stalls out. I'm thinking it is going rich because I cannot restart the engine after it dies. (Flooded?), but if I let it set for an hour or two, it starts right up and idles great. So I replaced my O2 sensor with a denso....still did it. My vacuum is at ~18hg at idle and it boost to 10psi (where I have it set). I know I don't have and vac/boost leaks so the next thing I looked for was an exhaust leak around the O2 housing. I made sure the O2 housing was tight to the turbo, I have a 3 layer metal gasket there. The only thing I saw was the gasket between the O2 housing and the downpipe looked like it may have had a small leak. I bought and extremepsi 6 layer gasket and installed it. Is there anyway to seal that up any better?
 
The front o2 sensor is the what the ecu uses in closed loop operation. Exhaust leaks from the o2 housing can most definitely throw off readings. The ECU produces a corresponding change in the o2 sensors voltage inputs from the O2 sensor and responds by changing the fuel mixture. In closed loop operation the ECU is using the o2 sensor’s input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean also known as cycling.

Deleting the rear o2 sensor will have no affect on an exhaust leak (from a tuning/running aspect). Its main function is to read a/f mixtures for catalytic converter operation. If removed, a CEL will be triggered. This will not change how the car runs. If you will to delete this, there are multiple searchable solutions that get rid of the triggered CEL.

As for the gaskets, it is important to make sure that the sealing surfaces are smooth, clean, and flat. Torque fasteners correctly/evenly. Nickel-based anti-seize will make removal much easier next time.

When you changed the front o2 sensor, did you disconnect the battery for a while? This resets the ECU.


How do your spark plugs look? How old are they? What is the gap?

Do you have a way to log what is happening?
 
Spark plugs are NGK 6's and they are about a year old by now. The gap is .28 ( or just factory gap) I have driven the car on these plugs for longer trips before this issue started. The only thing different is the car sat for 5 months while I was gone. I dont know if that would cause any issues? But the car runs great for 3 miles then it sputters and dies out. I will try and get a log this weekend.
 
What about the condition of your plugs?

Is your car running rich or lean? What are your AFRs?

If you know you have no boost leaks, what psi did you test to? How long did it hold?
I ask because based on your given information, you are just looking at your boost gauge while driving.

Have you verified that the new o2 is not cycling?

A coolant temp sensor can also be problematic if it is not operating properly.
 
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