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Sorry I haven't had much time to follow up on this. I purchased a 5 gas analyzer and while testing it out caught a chunk of snow and that destroyed the probe. Haven't been able to justify another $1600 for a new probe.
No doubt people are aware of carmakers pushing to move cats closer and closer to the manifolds. In fact many engines were redesigned to put the intake at the front so there would be enough space for a cat immediately after the head.
I managed to spend a couple of hours (and beer) discussing some of the eco-modder topics with one of a certain carmaker's engineers. One thing that was explained to me is that the GDI engines are the future since they're practically the only things that will pass all the more stringent emissions regulations coming down the pipe. These things can be programmed to essentially spit burning mixture out the exhaust on startup just to light the cat off quicker and meet the cold start requirements.
With hybrid cars like the Prius they have extra insulation and cat temp calculations are part of the engine control strategy just to ensure the average pollution is as low as possible. This explains why they can shut off and turn back on and still keep low emissions.
Finally I ran the pulse and glide idea by the engineer and he flatly said it is entirely false. Obviously people on here have managed to record gains with their pulse and glide thing but his description of the physics involved make sense. I'll try to describe it the best I can.
ICEs have different fuel requirements per unit of work. This is measured as brake specific fuel consumption BSFC. Generally, the higher the energy output the worse the BSFC is (within the operating range of the engine - I'm not talking WOT at 800rpm). To improve upon this carmakers even added extras like EGR to reduce pumping losses and many have switched over to electric power steering and such just to reduce fuel consumption. I might add that the losses of power steering are proportional to engine speed and on the highway then proportional to your vehicle speed.
Now, pulse and glide you accel to some speed, shut the engine off and coast down to some other speed then resume. The problem is that nearly all engines are designed to have the best BSFC at cruise, not accelration. In fact, EGR normally turns off during acceleration.
Since v=d/t the pulse/glide person is going to be travelling at some average speed. For some time they consume 0 fuel and for some time they consume an above average amount of fuel accelerating. The amount of work is the same whether you go fast or slow but BSFC, the engine's energy output and the losses (pumping, air resistance etc) are different.
At this point I got a bit lost in the calculus but since air resistance is exponential by the speed it turns out the friction from air resistance is greater when you are pulsing than the amount you save when your glide falls below the average speed.
Now, you've got more friction losses than someone cruising constantly at the average speed. The engine has to output a little more total energy than the average speed case. At higher outputs the engine is less efficient. At the end of the day more power out under less efficient conditions - P&G cannot possibly work.
I wonder why those who do it are recording gains or if anyone has ever done an objective test by figuring out their average speed with P&G and compared it to driving the same average speed. Or is it just some vehicles that did better while most do not? Maybe something older that doesn't have features like DBW and EGR?
The complicated engineering answer seems to say P&G cannot work. I've always questioned it myself. Can anyone describe how it possibly could work? Maybe it's a component of an overall driving style that as a whole provides gains?
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