UEGO bung location for aem afr gauge
 

OK, I have a stock cat on a 2.0 duratec. I will be purchasing the xcal 3 and aem afr gauge soon. For the location of the bung to install the UEGO sensor Is its ideal to install it as close as possible to the first O2 sensor of the header coming from the engine? Does anyone have any pictures on this that they can post?

Most say about 12-18" away from the block but before the cat.

If you locate it before the cat by (or close to) the 1st o2 sensor (the one that is threaded into the cast iron neck) your technically to close to the engine and it will burn up the wideband (that is what I read, although the discussion seemed to be tilted towards HP V8's). I tried to get info if it would be possible to locate the bung around the 2nd o2 sensor (the one located in the SS canister, but ahead of the cat supposedly). This would be better heat wise, but it may be to far out of the exhaust stream to give you a trusted reading. That leaves only a location after the 3rd o2 sensor (down by and right before the flex pipe). The issue is that you will be trying to read your A/F minus the A. And it is noted that as the cat ages the A/F reading will change. It is not possible to thread another bung into the cast section (I checked with some folks who would know). therefore, the best that is possible would be to have a SS 'cone' made with a bung that would position the wideband 02 sensor deeply enough into the SS canister and before the 2nd o2 (and after the 1st o2) and in such a manner as to negate the effects of the volume increase of the canister. To do this properly will require a sacrificial exhaust manifold that you can dissect to determine the proper points and dimensions. Most folks just go with putting it near the 3rd o2 (down by the flex) as it is weldable and accessible, and make a mental note that the reading is off by a few points.
Have fun with it. [wiggle]

just buy a header and put a high flow cat in your exhaust (check with local emission laws first). The stock manifold, cat and flex pipe are very restrictive. The tune will disable the rear 02 sensor. But you definitely want to put the wideband 02 sensor before any cats.

This would work except for >> The vehicle will (of course) immediately fail any emissions tests if required for all the obvious (legal) reasons. But just be aware that the main issue with moving the cat downstream is due to startup (when the engine is running at it's richest). The smog guys want the cat to heat-up as quickly as possible. We had a discussion about this a good while back (going so far as to contact the responsible parties within the Fed Gov). The answer was no, not with a standard cat. Now there is a type of powered cat (Tom gave me the type once) that could be used as it does not depend on the exhaust heat for warm up. But there very expensive. However, they are a high performance part, but I have never found one at any of the normal retail channels (note: I did not look that hard). I would be curious to know if these are even available in a size our focus could actually use. [wiggle]

Why would a high-flow cat cause you to fail an emissions test?

Jgrove998 suggested putting a high flow cat after a (aftermarket) header. That config will fail as noted.

Why though? Are HFCs less effective than OEM?

re-read my post. the issue is not the cat. the issue is the distance of the cat from the engine. [slap]

i have a high flow cat on my vehicle right now and i hate to say it but wether i have a stock manifold or a header on there it will be in the same place