docmirror

Both are true. It measures the free O2 in the gas stream, AND all those gases are byproducts of combustion.

At perfect stoichiometric ratio of 14.7:1, the free O2 is about 4% of the various gasses of the combustion event in an Otto cycle gas engine. That produces a reference voltage which is sent to the fuel injection ECU. The ECU is constantly adjusting the pulse width to maintain the proper ratio. Now - for bonus points, the ECU actually doesn't hold the ratio exactly static. There is a periodic variance built in to burn off the surface of the catalyst so that the cat converter will have a significantly longer lifetime( > 100,000 miles in most cases). The ECU typically will run slightly lean of 14.7:1 until it runs in burn-off mode, when it enrichens the mixture slightly so that the catalyst in the converter is refreshed.

merchauser

is it possible that a misfire, or a combination of misfires (all 8 cylinders at the extreme), could be misinterpreted by the knock sensors
and erroneously pull back timing? wondering if a poor ignition condition could lead to false knocks?

Speedtoys

Merc:

I put on new Beru wires today, and..my "leaving a light" and "Highway load RPM" rumble are gone.

Lets see if it sticks for a few days..but..this was the last part of the ign system I had not replaced yet.

merchauser

FWIW: new plug wires have made a significant and noticeable difference! idle was darn good prior; now incredibly rock steady.
more performance at 3k and again at 4k when flappy kicks in. I fought this for a long time, especially since I needed other parts
of higher priority. the wires are not cheap, but like a lot of other bits, most likely the last set I will buy. thanks roger!

Chuck Schreiber

SeanR

Just to add a data point. I've had many cars that had stumbles, rough running and a '90 that would actually stop running after it got hot. All issues taken care of with new plug wires.