Date: Sat, 11 Nov 2000 19:43:09 -0600
Reply-To: Darrell Boehler <midwesty@MIDWEST.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Darrell Boehler <midwesty@MIDWEST.NET>
Subject: Re: Digifant Operating Specs
Content-Type: multipart/alternative;
Hi Gary,
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.
Darrell
--- Original Message -----
From: Gary Stearns
To: vanagon@GERRY.VANAGON.COM
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?
Thanks-
Gary
[text/html]
