I suggest you read = the " Bosch Fuel Injection & engine management" = book. It does a good job of explaining various bosch systems and fuel = management components. This is not intended as a cop out it is the best = source of informantion about the questions and observations you mention.

The o2 = sensor voltage indicates a perfect mixture when it reads 0.5 volts. Max power = is slightly to the rich side , max fuel economy is = slightly to lean side. Least polution with a cat is right on 0.5 = volts. When the full throttle switch is closed our vans run at or near a max = power mixture. The ecu constantly adjusts the mixture when not at = full throttle to get a 0.5 volt reading. This is nearly impossible as = the o2 sensor is very sensitive to a perfect mixture and changes much when just a tad too rich or too lean. So we normally observe = the o2 sensor voltage bouncing above and below 0.5 volts, or we see it at about = 0.7 - 0.8 volts when at full throttle.

If you notice the o2 = voltage bouncing above and below 0.5 volts seveal times a minute = while you are cruising at a steady speed the mixture is probablly = ok. Once our ecus go into closed loop they tend to stay in closed loop. Once = the o2 sensor starts providing the ecu a voltage the ecu puts blind faith in = that voltage and will attempt to bring the voltage into range by = correcting the mixture.

To know for sure = your van is in closed loop hold the engine / tach at 3k rpm. You will notice = a slight rpm variation as the it slows slightly when lean and speeds = up when rich. This should happen several times a = minute.

--- Original Message -----

From: Gary Stearns

Sent: Saturday, November 11, = 2000 4:47 PM

Subject: Digifant Operating = Specs

Maybe only Bosch or VW engineers know = this, but the list has amazed before...Over the past few months, I have run our '88 = with the O2 sensor disconnected (open loop). I did this so that I could = manually adjust the AFM spring tension and wiper static setting and live with = it awhile under various conditions without fighting with the ECU. Lots of = fiddling later I do have open loop settings that allow the WBX to run = right. Rock steady idle (though cold is still an issue) and plenty of power. = Today I again connected a digital multi-meter to the O2 sensor while still = keeping it disconnected from the ECU. This setup allowed me to = drive with the multi-meter propped on the dash. I had found earlier = that our engine will not run right (too lean, stumbling acceleration, lousy = throttle response) with O2 sensor outputs in the .5 range where I had seen the = list suggest that they out to be. I find that my manual S.O.P. (seat = of the pants) adjustments have left me with O2 outputs in a fairly = constant (doesn't fluctuate too much) .75 to .88 range. I next = reconnected the O2 output to the ECU while keeping the multi-meter connection = piggy-backed as well. Now the O2 output changes quickly as = the ECU is trying to adjust. Output appears to go from .55 to .90. = A little more lean hesitation at lower rpms, but the high rpms seem to = run more cleanly.

My question (finally) is: what O2 sensor = output range is considered normal with the ECU adjusting things? I thought that the O2 sensor / ECU combination attempts to adjust for no = excess oxygen or a 0.00 voltage. Our WBX might run at this level, but = it would run terribly. At what output levels does the ECU go "out of = range" and give up defaulting to open loop again? With non-spec AFM = settings am I forcing it to go open loop or even fluctuate between open and closed?