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Installed Stahl header, AFR through the roof.

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Got the Stahl header installed.

Car ran fine before, 13ish afr, no issues.

Now cold idle is 17+, warm/hot idle is the same.

Intrestingly, I now have a very light exhaust fume in my engine bay. Checked head flange, collector on bottom, seals, NOTHING!

Yes, it's the correct header model (called and confirmed serial number).

Checked throttle linkage, all good.

Warm up regulator is good too.

Why would there be a change?

Why do I smell exhaust?

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heh- because the header's working???

Your airflow is so much better

that your fuel system can't keep up?

Seriously, though, a real improvement in flow through the system

WILL need more fuel. Usually not that much, though.

Unless you had a REALLY restrictive system before, and the stock

2002 system's not that bad.

The only constructive ideas I have are that maybe in the installation

you bumped something else,

or you have a gross leak in the exhaust system that's somehow sucking air.

I had some early Ireland E30 headers that had that problem- the flange

hooked on the bosses on the block, and they didn't seal at all. 15 minutes

with the grinder, and all was well.


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I think you have an exhaust leak somewhere which is letting in air and letting out exhaust -- explains the smell as well as AFR. At idle, the air inflow is not limited by the exhaust, but by the throttle valve, so changing header should have no impact.

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Back to basics. Where is your 02 sensor installed?

NOS Stahl header or used version?

I've ran across several older Roundel letters indicating the tii didn't like anything but stock tii exhaust manifolds.

This is why I am on the fence using mine.

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As mentioned, you have a leak somewhere. If you somehow don't, I'd check the sensor and make sure it didn't coincidentally die on you.

...Your car is going to sound great with the Stahl. I removed the egr from mine yesterday and have a nice hole in the header, but it will all be welded up tomorrow. I also have a header on it's way to go in... we definitely need to do some side by side tii vs weber comparisons ;)

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17:1 air fuel ratio is lean. At idle there is very little flow in your exhaust system compared to wide open throttle at high rpms. I don't see how a exhaust system change would do much to a four stroke engine at idle. But I am not a tii guy so perhaps you will teach me something.


1.Air leakage into the exhaust stream is the most likely culprit. You smell exhaust and air can leak into the exhaust. Wave dynamics in exhaust systems can do funny things. Because of this I would suspect a leak or leaks is located upstream of the collector. Excess air in the exhaust would also explain the high AFR. Make sure you check around the O2 sensor for leaks especially if you did not replace the crush washer when swapping the sensor to the new exhaust and or did not torque it to spec.

2. Is your sensor heated? Is it still working properly?

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Thank YOU all for contributing with suggestions. I am happy to report that the issue is resolved.

The fix was as most of you suggested - an air leak (literally a pin hole) in the exhaust - and in my case, before the O2 sensor.

Specifically, the leak was at the 4>1 collector (under the shifter) and once covered up - the car started up and ran beautifully. Unreal!!!! AFR was nice at cold idle and slowly crawled up to 13ish as it warmed up (in-transit pic below).

The header definitely sounds very nice - a little louder than the tii exhaust.

However, we should not give all the credit to the air leak. As reported by me in the post below, I installed some modifications earlier and had some initial issues. These have been resolved with the proper installation of the sticker and NOW, with the Tii motor + Stahl header + sticker i feel that i got a complete package and am ready for the track. : )


Thank you all again (the last part about the sticker is obviously a joke).

Have a great weekend everyone!


p.s. will post a video with the header sound this weekend under a separate post.




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