Dr.Mudge

Hmm, mayhaps, dunno. I remember in one truck's PCM that there was a cruise mode, that would only every several seconds (I think) check the O2s and look for knock, while in this cruise mode it would run in the 16.0:1 range or thereabouts. I remember awhile back people were wondering if it could be found in other PCMs also, but I believe it was taken out, or at least hidden, since this doesn't help pollution in terms of the tailpipe emissions only in less fuel used.

number77

Awasome, i am definitely looking foward to spending some late nights reading his stuff.

rskrause

Like most men, I am expert at three things. Of course, I am an expert driver (which includes knowledge of cars). That's the first. And my sense of direction is second to none. That leaves the third thing that I, along with all the rest of you guys, am in total mastery of.

Anyone know what it is?

Rich Krause

4drLT4

Your own domain...perhaps?

Eric Bryant

The problem is that they're kinda slow, so they're typically used with a load-brake dyno. I don't think they'll work fast enough to be used with a powerful car on a inertial-type dyno.

Lean-burn isn't used on OEM PCMs anymore, as the feds cracked down on it (lean mixtures tend to increase the oxides of nitrogen). To the best of my knowledge, GM hasn't included that strategy in their PCMs since the days of TBI.

The dithering above and below stoich wasn't originally designed to aid the cats (which, at the time, where two-way devices); it was simply the result of overshoot in the control algorithm due to a slightly underdamped condition (which was necessary to react quickly enough to "noise" in the system; damping all the oscillations would have made the time constant of the system unacceptably slow). The two-way cats only needed oxygen, which they got either from the lean portion of the oscillation or an auxilary air pump. Later, when three-way cats came along, the rich portion of the oscillation became useful again (as it's somehow used in the reduction of the oxides of nitrogen).

cmillard

Hey Eric, Really like what you've done with your webpage, good pics, good info, thanks for sharing.

Good Point on the 4-5 gas analyzer, it wouldn't refresh fast enough for WOT, but it's invaluable for part-throttle tuning, I know a shop that uses one all the time.

Thanks,
- Christian

PoorMan

I have a paper on 02 sensors if ne1 here is feeling geeky.
It's pretty good.

Jeff D.

Eric Bryant

We're always feeling geeky around here Share away!