Emission's woes...

["Storhok, Eric (E.M.)" <estorhok@domain.elided>]

Ok, Tess, here is an idea.

Your exhaust leak is the problem.  Didn't you mention there was a crack in one of the headers?  

Here's maybe why: the leak is making the sensor think that its generally running lean, so it richens the mixture.  Not steady state, but switching properly.  What this does is bias the overall mixture to the rich side while still switching between rich and lean as intended.

So, as Ian pointed out, HC usually goes along for the ride.  But not always- I have seen in the lab a case where biasing the mixture rich has no effect on the outcome of the test besides adding CO to the final result.  Yes, this is odd, but it does happen.  All I need to do it multiply my results by about 100, and its very similar to what you have.

Even though I said that my NOx did not go up, I would think in this case, NOx would be slightly high, simply due to the extra O2 in the exhaust coming from the small hole.  And it is a small hole in front of the sensor, yes?

CO can be a big pain, as you can get conditions where it just does NOT want to convert, but everything else will be fine.

One other judgment- if after the fix, your HC numbers are similar, your catalysts are on their way out...

Eric Storhok
Core Emissions and Fuel Economy Team
Advanced Powertrain Engineering
(313)33x75011
MD 35, FPC-B
Ford Motor Company

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