o2 sensor question 79 ca bay

[tolkien]

checking the afr #s on my bus with a borrowed LM-1 (thanks Randy in Maine) and all looked good.
then i decided to check the o2 sensor per Bentley manual( very last page i think)
when i disconnected the o2 sensor the bus went super lean??
from 14.5 to 16/17:1. hook it back up.. and back down to 14.5 or so?
so the sensor is making it rich....0.5 to 0.7volts tested at sensor.
i disconnected the o2 sensor and tuned it back down from the very lean conditions to 14.5 or so at idle and at smog test speeds alright!
i thought after i re-connected it the 02 sensor would just smooth the afr out a bit more so to speak. but nada! it enriched the mixture//12:1 or so
I really dont get it. I got to get this meter back to the owner asap.
im stumped.

thanks for any ideas.
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79 ca transporter

[mikedjames]

It is written elsewhere that the optimum AFR for running on this engine is about 12.5 . But that is not best for pollution.

Maybe somebody has messed with the FI system to make the engine better.
Or the FI system has drifted off.

[SGKent]

Any O2 sensor with more than 75,000 - 100,000 miles on it should be replaced.

My best guess is that the smog system is programmed to run lean when it is disconnected. This would prevent everyone in sight from removing the O2 sensor wire to make it run richer.

It is extremely hard to make an O2 engine run at anything other than 14.7:1 when it is working unless one hooks up a device like a LM-1 that lies to the ECU what the mixture is.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[tolkien]

o2 sensor is less than 3y/o, not many miles (sadly)
now that the o2 is disconnected and i set with lm-1 to 14.5 or so, (i had it at 14.7 at one run)..at idle for example....but if i plug in the sensor, the afr drops rich "2 points" approximately 12:1 range.
if the afr is "right on" why would the o2 need to do anything with the mixture?
at this point im probably out of time with the meter. so...
would you guys suggest running it 02 disconnected or re-connect and re-set the afr back to where it was? i passed smog 1.5 years ago with that setting. i was trying to "get ahead of the curve" with this venture and now i found myself wondering wtf again. i thought i had i dialed etc
thanks for all your help!
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79 ca transporter

[airkooledchris]

im extremely interested in running this same test on my setup. I just replaced the O2 sensor on mine but have a feeling it isn't doing anything at all, as there seems to be no difference in how it behaves when it's connected/disconnected.

I didn't have my LM-1 anymore when I got around to testing my 79CA bus setup, so I can't say what's actually happening.

SGKent - do you have an LM-1 still? I might pass through your area next week on my way to the bay for the weekend. (Probably later Wednesday the 16th)

I have one AFM dialed in for perfect loaded up/highway driving. I can cruz all day loaded up and still not hit much over 400* CHT's. What id like to do is tune my spare AFM and reconnect the O2 sensor the rest of the time. I doubt it'll do a whole lot for my MPG, but if it helps a little that would be nice - but mostly so im not a nasty pollution machine when I don't need to be for CHT's.

[SGKent]

how are you using the O2 sensor for the LM-1 and also for the ECU at the same time? Where and how are they mounted?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[tolkien]

the o2 sensor is in the stock factory port and the lm-1 test sensor is plugged into the cat (bus boys 5-6 y/o) there is a port (normally just plugged) upstream side of the cat.
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79 ca transporter

[Amskeptic]

[tolkien]

thanks for the help guys. this is what i thought as well. when i first disconnected the o2 sensor the ratio jumped to 16ish form my "smog in ca passing settings" of 14.7ish in all test speeds.
i thought maybe it was too lean and the o2 has been really working to richen the mixture.
so i thought" well ill set the mixture right without the o2 connected and that will make things even happier.. but when i reconnect o2 to the seemingly good afr at idle for example......the o2 will richen it further 2 points or so. i hope this makes sense. 12:1 ratios..it seems to make things richer regardless of what it "sees".
i do the free air calibration each time i go. remove and expose to open air.
hold the button 2 secs.
also. i have an analog meter and a dig meter . i checked the mv at the sensor wire, i get 0.7 mostly(not in line) and 0.5 to 0.7mv when in line with o2 connected. i dont see the mv bouncing up and down however as i thin kit should, as soon as i touch ground its .5 then goes up and stays at .7 ???
the wiring checked out too, o2 sig wire to #24 on the ecu 0 ohms..even shook it around.
sig wire to grnd 0 ohms

Ive been tracking my mileage a little and it is definitely an the poor side
11-12mpg i got 100 miles on 9 gallons estimate last time...in town stop and go driving lots. gotta be related.

thanks for the help everyone..i gotta run into town back in a couple hours..
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79 ca transporter

[Randy in Maine]

You hang on to that LM1 until you get this figured out. I am good with that.

I like to defer to how the engine runs before I trust the meter too much.

[Wildthings]

I am going to take a wild shot here. Supposed you have a misfire going on, the O2 sensor for the AFM will see that as a lean condition and dumps in more fuel to bring the mixture it sees to 14.7:1. However by the time the exhaust gas passes through the cat the extra oxygen has been consumed so your LM-1 sees a much less free oxygen and says you are running rich.

[tolkien]

Randy thanks again.
I was gonna send it back and then i read that last section of bentley again, and i thought i would just do it to further verify things were par!. and so it goes..maybe its been wrong the last year and a half? It is running well enough. did always had a sluggish idle at cold start up. strangely this seems to have improved greatly without the 02 sensor.
A "misfire"? would this be easily evident? i changed all the plugs three weeks ago. they looked tannish. pls keep me going here. I am not a car guy really. Everything ive learned over the last decade has been here on the samba and other sites. thank gods! So I could be missing something obvious too.
i did the propane trick over possible leak areas and noticed no engine change anywhere. i was thinking vac leak and has been compensated to the point where the afr measures good with all the extra air...lots fuel to match the amount of air and this would show the bad mpg as well, but like i said I am guessing here.
** (wildthings) I think the lm-1 is reading the exhaust "pre-cat".

keep em coming.
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79 ca transporter

[SGKent]

I have 2 Bentley books. One goes to 1978 and the other 1979. The last page in the 1979 book, page 34, explains everything you need to know how to set it as well as the condition you are describing.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[tolkien]

thanks SGKent. im really confused.
so according to that page.."if the CO level is still too low (lean)" I might have an exhaust leak?
Is this what your thinking?
does that mean air is getting sucked into the exhaust. sensors are seeing it and adding fuel...=bad mpg too..
what other symptoms would i find with the exhaust leak?
still ...
why would the test sensor and the stock o2 sensor see things differently?
and, i guess i really cant tune the afr till this is remedied?
what the best way to check..
ive tried the drive by a wall and listen for sound change( i think muir book)
and quickly covering the tailpipe and listening
any other tips?
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79 ca transporter

[airkooledchris]

if you just ditch the sensor you can tune to your hearts delight.

[Wildthings]

Can you rig up a way to swap the two oxygen sensors?

[tolkien]

the two sensors are about 4 inches apart. would it be possible it is that positional pf a problem?
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79 ca transporter

[airkooledchris]

there's no getting around it, if you really want to know your going to have to compare it to a new sensor. I got mine at busdepot on sale, less than $40 I believe.

[Randy in Maine]

I think both O2 senders (on your bus and in the LM1) are 1 wire Bosch units. Can you plug your exhaust mounted sender in the LM1 or the LM1 sender into the exhaust mounting location of your engine O2 sender?

In the real world these are usually permanently mounted to th eexhaust system further up so that you do not get O2 "creep" in from the exhaust mounting.

[tolkien]

thanks randy.
just change their positions, right?
ill try it asap. got a bunch of stuff going on as well right now of course.

one question.. I have read there is a "blip" of lean condition from the throttle plate opening up at times. up gearing etc how long does this last?
i notice it in my drive/readings and it last 5 secs or so at times. does not seem right.
it will find its way down to 14 ish , but it takes longer than seems wel
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79 ca transporter