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From: John De Armond
X-Source: The Hotrod Mailing list
Date: Mar 1992
Subject: Re: Port Fuel Injection

>> Instead of trying to maintain
>>stochiometry, I would be trying to maintain a mixture curve known to 
>>produce the best power in that engine.  This will require some changes
>>to the lambda sensor.  A normal sensor has a very narrow range of 
>        ^^^^^^^^^^^^^^
>	Ok, I give up! What is the Lambda sensors function in life?

Lambda is the proper name for what is commonly referred to as an oxygen
sensor, the little zirconia and steel thingie that screws in the exhaust
manifold and generates an output proportional to the lambda of the exhaust.

Ok, so what is Lambda, you ask?  Easy.  Lamdba is simply the ratio of
the current fuel:air and ideal (stochiometric) fuel:air ratio.  Thus
a lambda of 1 is stochiometric.  A lambda less than 1 is rich and 
more than one is lean.  A common term used in fuel injection circles is
reciprocal lambda or gamma.  This is convenient because it is >1 for


From: John De Armond
X-Source: The Hotrod Mailing list
Date: Mar 1992
Subject: Re: Port Fuel Injection

>Ok, so I guess I'll have to stick my neck out a bit and see who hacks it
>off :> [ This would be a better question for, but
>somebody'd say that their chevy lambda sensor is better than your ford
>lambda sensor and the italian lambda sensors are _really_ fast and ... 
>Or, but aint' got one yet either. So... 

Nah, there's no intelligent life in*.  We're all over here now :-)

>So, just what _is_ the ideal fuel:air ratio of the exhaust?  I'd be
>inclined to suggest 0!  But seriously..

Not the fuel:air ratio of the exhaust but the intake.  The answer is
it depends :-)  "gasoline" has been considered to be stoichimetric at
a ratio of 14.7:1 air/fuel.  Actually depending on what "gasoline" really
is, this can vary from 14:1 to 16:1.  Methanol is 11:1.  That's why 
you have to dump buckets of methanol in an engine.  That's the beauty of
lambda. Regardless of the actual stoichimetric ratio of a particular fuel,
the deviation for stoichimetric will be reflected the same in the sensor

>Can somebody explain this more?  I assume the thing most directly
>measures oxygen? Exactly what is this taken to indicate?
>Ultimately, you seem to be saying it's an indicator of fuel/air?

Yes, the sensor directly measures the ratio of oxygen in the exhaust
to the oxygen in a reference chamber normally vented to air.  Oxygen
concentration directly relates to fuel/air ratio because we know
how much percentage of air is oxygen in the intake and therefore 
"compute" (in the chemical analog "computer" that is the sensor)
the oxygen used to burn the fuel.

>What is stochiometric? Ideal fuel/air?  "Ideal" in what sense? a
>universal constant? parameterized by engine type, rpm, temperature...?

By definition it is the ratio where the fuel is exactly completely 
consumed by the oxidizer present (normally atmospheric oxygen.)
This is a chemistry term and not an engine term per se.  It just so 
happens that as the mixture passes from rich, through stoichimetry
and on to lean, the CO and HC emission declines while the NOX stays
low until the lean side of stoichimetry.  All three are sufficiently
low at stoichimetry that a three way cat can clean it up.  In fact
the three way cat REQUIRES stoichimetry in order to work.  (Please
don't ask me to do a disseratation on THAT subject :-)

>Unless this seems wildly inappropriate or boring, I'd like to hear more!

Only boring if we're talking about damned old Ford sensors.  Or was
that chevy sensors... I'm so confused....


Date: Thu Jul 16 12:42:33 1992   
Subject: Re: gauges issues 

In you write:
>I understand that these oxygen sensors are not that accurate
>for the reading you really need to provide the correct information
>for a good stoichiometric reading, unless it's one produced
>by some Japanese transducer manufacturer.  It suppose to cost
>over $2,000.  Is this information correct?  

No.  Horiba (the japanese maker) makes a very wide range unit which 
uses a special transducer to cover almost the entire range of combustibility
of gasoline.  Not needed for mixture dithering.  An ordinary zirconia
sensor, though fairly narrow ranged around stochiometric, is adequate
for tuning.  Maximum WOT power mix is always determined experimentally 
and will not correlate to a specific ratio.   

>Also, does anyone
>know what is the minimum sample rate for one of these transducers
>to over come the noise function produced?

Not sure what you are asking.  A typical zirconia sensor has a response
time constant of under a millisecond.  Yes, individual cylinders can be
seen on a scope.  Most of the bargraph displays use the LM39xx bargraph
display  that is an analog device and thus samples "continuously."
About the best price I've seen on these things, BTW, is from Summit
Racing.  Compudyne has a dashmount unit for $29 without the sensor.


From: dlogics!!acg@uunet.UU.NET
Date: Mon Sep 21 12:04:48 1992
Subject: Re: Ford Ox sensor number

Let me add a brief followup note to DJE's excellent oxygen sensor article...

Whenever a Motorcraft part number (e.g. DY-606) is assigned to a standard part
number (e.g. F0SZ-9F472-A), it indicates that the part is available over the
counter as a retail maintenance item at well-stocked auto parts stores. You
should not need to stand in line at the parts counter of a Ford dealership for
it unless you strike out elsewhere first. (i.e. Buying a Motorcraft DY-606
oxygen sensor is like buying a Motorcraft FL-1A oil filter...) By extension,
you could then shop around for aftermarket (i.e. "even cheaper") replacements
for Ford's DY-606, although perhaps we are straying a bit too far afield from
the original part now...  :-)

Andrew C. Green
Datalogics, Inc.      Internet:
441 W. Huron          UUCP: ..!uunet!dlogics!acg
Chicago, IL  60610    FAX: (312) 266-4473

From: "Mellum Ron" <emory!!mellum_ron>
X-Source: The Hotrod Mailing list
Subject: O2 Sensors: Again
Date: Thursday, Oct 22 1992 11:15:25

One small question on Oxygen sensors:  What is the typical response time of a
sensor?  The reason I ask is this, if one was to design an O2 sensor monitor
how often would you have to go out and get updates?  I realize that around the
stoich. point change is greatest.  In the case that I'm interested in,
"response time" is defined as the time it takes the sensor to react to a change
in the A/F ratio.  Along that line, are there typical output voltages for
values of the A/F ratio (at a given sensor temp), or does this depend on the


[If the sensor is good and hot, the time constant is typically a few
milliseconds.  Yep, you can see the individual cylinders at idle.  I've
built a little rig that explodes about 20 cc of propane/air in order to
generate a combustion square wave to measure the response time.  I'm not sure
yet whether I'm measuring my O2 sensor or the propagation of the combustion
gases :-)  For a standard zirconia sensor operated in voltage mode,
the voltage swings from 0 to 1 volt in a range of about 1/2 A/F click
around stoch.  JGD]

From: John S Gwynne <emory!!jgwynne>
X-Source: The Hotrod Mailing list
Date: Feb 1993
Subject: Horiba Inst, UEGO, BMEP, BSFC, life...

On Jan 7, 1993, the following exchange transpired regarding
the use of oxygen sensors:


Today I talked to a Horiba Instruments representative. After I convince him I
did not wish to buy a MEXA110 analyzer for $8800 he informed me that the most
inexpensive UEGO bases analyzer was approximately $2500 :(. This unit was not
even a standard catalog item, but rather a special item used to test race cars.

[Yes, they had this stuff on display at the PRI show.  $2500 is list; they
intimated that selling price was much less.  JGD]

During our discussion, I was told that Horiba and, I believe he said, General
Electric teamed together to develop the first UEGO sensors in the '70s. Since
then, NGK, under some sort of agreement, was selected to produce the current
sensors. He implied that NGK would not be able to directly sell UEGO's. The
sensor itself with no electronics cost roughly $900 :( , and this was
apparently due to the low production volume. I could tell he was "dying" to
sell detroit on the idea of using these in there cars due to the wider fuel/air
ratios covered. In passing I mentioned the above Motes reference, and the
response was of the sort "... if anyone else is using a UEGO for this type of
application, *I'm going to sue them* ... we own the rights ..." Any how, I've
found myself discouraged on the prospect of obtaining a UEGO.

John, $250 for the sensor and electronics? Is it possible that these
analzyers were indeed lambda sensor based?

Who/where/what is Motes?

[Boy was that guy full of &#$%^*.  Here's a quick brain dump.

Motes is made in Astralia and imported by JGM Automotive tooling, 5692
Buckingham Drive, Huntington Beach, CA 92649, 714 895 7001.  Person I
chatted with at PRI was Jim Munn.  Jim indicated they use a inexpensive
Bosch sensor that must be a new development.

Horiba Inst 3901 Varsity Drive, Ann Arbor, MI 48108 313 973 2171.
Person I chatted with was Rob Stawarz.  He told me the marketing manager
is Don Johnson.

On the UEGO, here is a bunch of information.  There are 2 major SAE papers of
interest, 890299 by several scientists from Hitachi, and 860409, again
by engineers at Hitachi.  A related paper is 860408 on how to drive a
conventional zirconia sensor over a wide range using the pumped current mode.
These are in the 89, 86, and 86 editions of "Sensors & Actuators" from SAE
or can be bought individually from SAE.

I also have on hand, compliments of "a friend" who may identify himself
if he so desires, some information that may be proprietary.

One item is the data sheet for the NTK #TL-7113 UEGO sensor and #TC-5111
control module.  Each sensor and control module is individually
calibrated.  The cal sheet example covers a range of 10:1 to 19.6:1 on
gasoline.  That pretty much covers the range of flammability for gas :-)
The notes on the drawing note that the sensor and the control module is
made by Ceramic Sensor Co, ltd, of Japan for NGK sparkplugs.

Another item is a letter from Epcom Corp, PO Box 47032, Oak Park, Michigan
48237, (313) 257 0627.  This letter covers the data sheet for the company's
Model 10630 air/fuel analyzer.  The picture looks a lot like the NTK  unit
but with a microprocessor to linearize the sensor and a digital display.
It is built into a Hammerlund cast aluminum box.  The price is listed
as $1247 ea or $987, quantity 10 (anyone interested in a bulk order? :-)
The unit has a display and a voltage output.  Range is 8:1 to 25.5:1.
The data sheet notes that it will accept either the Hitachi or NGK sensor.

How's that for a brain dump? :-)


Form "Holley Carburetors and Manifolds" by M. Urich and B. Fisher, maximum
economy is near 16:1 and maximum power approximately 13.3:1 (based on maximum
Brake Mean Effective Pressure (BMEP) and minimum Brake Specific Fuel
Consumption (BSFC)). In addition, the reference states that mixtures as lean as
18:1 are sometimes approached when seeking peak economy at high engine speeds
and low loads. The Edelbrock air/fuel ratio monitor works over the range 12:1
to 15:1. Not much overlap :( . Are there other portable *calibrated* exhaust
gas analzyers with a broader air/fuel range for less than, say, $500?

Finally, BMEP and BSFC in the above reference did not have a labeled y-axis.
Just how much do these quantities change as the air/fuel ratio is varied from
18:1 to 13:1?

John Gwynne

From: emory!!dave.williams (Dave Williams)
X-Source: The Hotrod Mailing list
Date: Feb 1993
Subject: How to detect/prevent leaning out?

-> leaning out the fuel mixture while under boost.  Is there some way I
-> can measure the fuel mixture?  Maybe some sort of sensor in the
-> exhaust? How about exhaust temp?  Will it raise and lower dramaticly

 An oxygen sensor in the exhaust would probably be the simplest way to
see if you're running too lean.

 You might also order a copy of B&M's Blower Handbook.  It's slanted
toward B&M products, of course, but it has an astonishing (well, to me
anyway) amount of good, useful information on blower setup, tuning,
and the like.  My copy was $6 from a local speed shop's book rack.

[I meant to mention in my brain dump previously, a very reliable method
of measuring A/F ratio on a fuel injected car is to measure the output
of the MAF sensor for air and compute the fuel flow from how long the
injector is open, and the flow capacity of the injector,
and do a simple division.  IF you use a GM MAF whose output is a variable
frequency pulse train, you can do the whole thing through the parallel
port of a PC. Just use the microsecond timer code from my fuel injector
flow bench software and tweak it around to read bits instead of outputting
them.  Hook the injector signal through a diode pointing toward the
computer to one bit and the MAF to another and measure when the bits
change.  JGD]

X-Source: The Hotrod Mailing list
From: John S Gwynne 
Date: Tue Mar 30 11:11:25 1993
Subject: Edelbrock air/fuel ratio monitor


I just bought the Edelbrock air/fuel ratio monitor and hears what I discovered.
The sensor is a Bosch PN E971-9F472-AA (a lot of numbers stamped on it, I think
this ones the Bosch part number). I believe this to be a standard three wire
conventual O2 sensor though admittedly I do not have the manufacture's
literature. The "little black box" is nothing more than little and black.
Inside there is a surge suppresser, a filter capacitor, one needed and one
redundant resistor to control the LEDs brightness, and a LM3914 Dot/Bar Display
Driver. The design is straight out of the application books with no creativity.
Did I mention the lack of input signal conditioning/filtering to remove engine/
ignition noise? Given the speed of the LM3914's comparators, this is a problem
and certainly a problem in my implementation.

   The electronics clearly runs the sensor in the voltage mode drawing only
a 25nA biasing current for the LM3914's internal buffer. The sensor voltage
and air/fuel ratio have the following corresponds:

                      volts      air/fuel     Lambda
                 (open circuit)
                       .250       15.0:1       1.02
                       .375       14.5:1       0.99
                       .500       14.0:1       0.95
                       .625       13.5:1       0.92
                       .750       13.0:1       0.88
                       .875       12.5:1       0.85
                      1.000       12.0:1       0.82

From what I have read in the SAE Transaction pertaining to O2 sensors, this
relationship is "bull shit". :( I can not believe this mode of operation would
let the sensor go as low as .8 lambda let alone have this type of linearity.

I would have at least expected Edelbrock to use a current mode of operation.

Any comments?

My next step is to change Edelbrocks "little black box" into a current
mode of operation and call NGK in hopes of finding an affordable UEGO.

John S. Gwynne

X-Source: The Hotrod Mailing list
From: John S Gwynne 
Date: Thu Apr  1 12:39:23 1993
Subject: Re: Edelbrock air/fuel ration monitor

Bob Valentine  writes:

>     From the tone, I can tell that the design is not a good one.
>However, I'd like to get away from the DVM hanging under my dash....
>Would using a 3914 (I used those in grade school for really cool audio
>power meters...) suffice with a 1 wire O2 sensor?

From what I've seen so far the electronic portion needs some improvements. The
input signal will have to be conditioned/filtered to gain a steady display. The
signal line from the sensor has no loading at all to reduce ignition noise. In
addition, I do not like the voltage generation mode of operation. From some of
the generic voltage-vs-current curves (as a function of lambda), in the SAE
transactions, I intend to find a load line that will maximize the sensor's
dynamic range and hope it works well for this sensor too. In the circuit to do
this, I will include some filtering. The use of the LM3914 is a good choice,
but I don't see it doing the job alone for a 1 wire or 3 wire sensor.

>  [chart showing voltage, air/fuel, lambda deleted]
>     So then, is this chart valid?

I don't think so. IMHO I think Edelbrock wanted a product to match MSD's O2
sensor, which has only one tri-color LED to indicate the mixture condition.
Their gimmick was to add more LED's and who would know if these LED's had any
real meaning? They almost flash in a believable fashion.

>     I don't have the reference here anymore, but I belive a LM3915
>works on current, rather than voltage.   Nice thing about this series
>is that you can chain several of them together to get a rather precise
>display. (ie., a 20 segment display... hell, just carpet the dash with
>those plug in segments! 8^>)

The LM3914 has a linear display and the LM3915 is logarithmic. Both are a
function of input voltage, and both will let you carpet the dash :) .

>     If you can find a UEGO, let me know.   Last I heard they were
>made of "Unobtanium", and way out of bounds on price.

The data sheet I have from HORIBA on their UEGO sensor for the MEXA-110 says
it's made of zirconia and ceramic :) . But at a price of $900, it is
unobtainable. If I can find the time, I'm still going to look for an affordable

[I mentioned awhile back the MOTES A/F analyzer that competes with the MEXA
but costs less than Horiba's sensor.  They told me they were using, I believe,
the Bosch UEGO sensor that is much cheapter than the one Horiba uses.
Someone else noted that one model of Honda lean burn engine uses a UEGO.
Might want to check the archives for that info.  They're at

John S. Gwynne

From: Dan Malek <emory!gatech!!dan>
X-Source: The Hotrod Mailing list
Date: May 1993
Subject: Re: O2 sensors, M85, stoichiometry
X-Sequence: 5275

> Date:  Mon, 10 May 93 03:04 EDT
> From:  Jonathan Lusky
>Anyone here ever used a zirconia O2 sensor with M85?

From my documentation, it appears that Ford uses them on their M85
flex-fuel Taurus.

>Should stoich still be approx .5v (how bad is the hydrogen
>shift with methanol)?  Right now my engine is running like

It seems to me that regardless of the gazintas (gasoline vs. methanol),
the combustion process should result in the same gazottas (mostly CO2
and H2O, plus the other NOx, aldehydes and stuff).  The O2 sensor
should be OK.

>crap, and won't run at all unless O2 sensor voltage is > .8v.
>Could I have somehow damaged the sensor in such a way that it would
>be reading high?  I know my voltmeter isn't the problem, since
>I get the same numbers from an oscilliscope.  Anyone know the
>stoiciometric A/F ratio for M85?  Hydrogen/carbon ratio &
>oxygen/carbo ratio?

As I recall (and this is a little foggy) from watching the 100%
methanol engines on the dyno, they run an AFR somewhere around 10:1.
I can only guess that M85 will be somewhere close to that, rather
than the 14.7:1 for gasoline.

[Automotive Fuels Handbook lists stoich for methanol as 6.45:1 and
the best power full throttle mixture of around 4:1.  That fits pretty
well to my rule of thumb experience of 3X enrichment over gas.  JGD]

I will go into my experiences with O2 sensors, so you can tune out at
this point if you are not interested.  I have found that you can't
run an engine at stoich all of the time (I was aware of acceleration
enrichment and running rich at WOT, but there is more).  I have found
that at idle and very light engine loads (i.e. air flow is below some
low water mark level), there is no way an engine will run at stoich,
you have to run it rich.  After an acceleration phase, I don't hop to
the O2 adjustment too fast.  The extremely rich condition (to the sensor)
will cause you to slam the AFR way too lean, and the engine will do the
choke and puke until your algorithm settles down.  You have to slowly
work into the O2 adjustment.

There is also some lag in the closed loop feedback.  Some engines are
worse than others, but the point is that you don't actually maintain
the set point of 0.45 or 0.5 volts.  For example, if you detect a rich
condition and start to lean out the injectors, when you get to the set
point the injectors are running much too lean.  You start making it a
little richer, but the O2 is lagging and it continues to tell you lean
and by the time it swings back through stoich and to rich, you are really
running rich.  Part of the problem is the very non-linear nature of the
sensor.  The other part is that "really rich" to the sensor is about an
AFR of 14.5:1 for gasoline, and "really lean" is about 14.8:1.

I have about a dozen different algorithms, and the very simple seem to
work the best.  Here is what I do, and I hope someone can tell me how
to do this better.  Below a certain air flow low water mark (and especially
at idle), I don't even look at the O2 sensor.  I rely on the injector
maps and other sensors to get the injector pulses to make the engine run.
The O2 is pegged big time rich at this point.  After an acceleration
phase that caused enrichment, I wait about 100 engine revolutions using
the injector map and other sensors before engaging the O2 algorithm.
This seems to cure the lean out condition right after the enrichment.
When running closed loop, you don't want to sample the O2 and make
adjustments too quickly.  Things just don't happen that fast in an engine,
especially when you have more computes than most folks have on their
desks.  I sample the O2 once per engine revolution, and make a very small
change in the injector pulse width.  My current algorithm computes a
percentage change, which is adjusted up or down depending upon O2 value.
It can handle both positive and negative adjustment from the current
injector map value.  The change is very small.  I can adjust the injector
pulse by as little as 0.4%, and that is the granularity of the change
once I am within the mostly linear "window" of the O2 sensor.  A very
small change in the injector pulse width makes a big difference at the
O2 sensor.

[I can see a couple of problems.  First off, you probably need to
do a composite sample on the oxygen sensor.  It is so fast that if you
sample it only once a revolution and use that value, you'll likely only
see one cylinder and it could vary significantly from cycle to cycle.
If you have the CPU cycles, you should sample the sensor several times
per revolution and run a sliding average.  If you don't have the CPU cycles,
build an analog low pass filter into the sensor circuit that will average
over a significant period of time.  JGD]

That's enough writing for now.  This is working pretty well for
me, but it changes a little from one engine to another.  I am looking
for more suggestions, also.

Now, can someone tell me how they do FI enrichment when coming off of idle?
I can get it right about 90% of the time, but I always find that 10%
when I pull out in front of some big truck.

[What is the configuration of the injectors and intake?  Is much of the
intake manifold wetted?  These problems you've described sound exactly
like the ones I've experienced with throttle body injection.  A whole bunch
of fuel must be injected to wet the manifold in addition to that needed
for acceleration enrichment.  The enrichment wave form looks like a
tail pulse.  Sharp rise and a slow decrease to the new steady state
value.  Closed loop control is greatly complicated by this delayed
fuel transport mechanism.  JGD]

	-- Dan

Date: Wed Jul 14 17:53:20 1993   
Subject: Re: O2 Sensor Mix Analyzer 

>Could someone resend the information on how to build a homebrew
>exhaust gas analyzer using an oxygen sensor?
>[About the best you can do with a standard O2 sensor is make a "rich-lean"
>indicator.  The sensor's linear range is very narrowly centered around
>stoich.  All you need is a high impedance voltmeter that will read in the 
>0-1 volt range.  JGD]


A rich lean indication would be good enough, I think.  Could you supply more
details?   What vehicle(s) have cheap sensors that would be appropriate?
Will this scheme work if I am sampling the exhaust at the tailpipe after
a catalytic converter?  How do I get the sensor up to operating temp. ?

Thanks again.

[Probably the cheapest way to get an indicator is to buy the Cyberdyne
dashmount unit.  About $29 from Summit, etc.  IF you want to build your
own, all you need is a high impedance meter circuit with a range of 
0-1 volt.  0.5 volts is exactly stoich.  A mechanical meter with an
op-amp buffer will do, as will the LM3910 barcode driver IC (available
from Radio shack.  You'll need to buy a self-heating (three wire) sensor.
Most car parts places carry generic replacement units.  The self-heating
one works just fine sampling the tailpipe though you do have to protect
the sensor itself from exhaust gas.  This is because the sensor must have
a clean air reference around where the wires come out.  JGD]

From: John S Gwynne <emory!!jsg>
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: Oxygen sensors and DIY instrumentation 

   In message <> , you write:
|    Could you explain exactly what you mean when you say 'short' the 
| output of the O2 sensor.  Do you mean right to ground?  Are you
| talking about when you physically have access to the leads of the
| sensor and simply haphazardly short it? :-)
| 				- David (

Well... yeah (red face :) ). When you put it that way, it sounds kind of
"stupid."  I don't know what the failure mode is when you do this, but I
ruined one sensor to what I attribute to an accidental shorting of the output
to ground. At the time it didn't occur to me that with the engine and
electronics off that the hot sensor was still alive.  Of the T.F.HEGO (3-wire
thick-film heated EGO sensor) I played with, all had a floating heater. So I
now just tape the leads together (out-of-the-way) after a test.

Speaking of failure modes, SAE paper 860478 "Poisoning of Zirconia
Exhaust Oxygen Sensors by Silica" has some interesting information.  A while
back someone asked why their EGO had a negative output voltage. One
possibility is silicon poisoning. Poisoning on the air reference port of the
sensor can cause the lean and rich voltages of the sensor to decrease.  The
output can even go negative. Poisoning on the exhaust electrode will cause an
increase in the overall output voltage for a given air-fuel ratio.  The first
can occur if silicone rubbers are used in areas near the sensor which get too
hot.  ie: don't put a protective silicone rubber boot around your sensor :).
The latter exhaust electrode poisoning has been link to two sources: 
(1) Gasoline. Outbreaks of sensor poisoning have been observed in Detroit and
northern Florida were Silicon levels as high as 500ppm have been confirmed in
the gasoline.  (2) RTV form-in-place gaskets.  If an RTV gives off excessive
silicone containing volatiles, they can be absorbed by the engine oil which
revolatilizes when the engine heats up. The vapors are drawn into then
combustion chamber through the PCV system and silica formed.

                                       John S Gwynne

From: John S Gwynne <emory!!jsg>
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: silicone, O2 sensors 

   In message <> , you write:
| I would bet that it's the acetic acid fumes from RTV silicone rubber that
| screw up the O2 sensors and not some mysterious silocone containing volatile.
| Most silocone oils or rubbers are very stable and are not very volatile at
| all.  There is a big difference between siloxane polymers and silica which is
| what glass is made of.  Most siloxane oils have very high boiling points, so
| I doubt if even uncured RTV silicone has any silicone containing volatiles.
| I know there are RTVs that are guaranteed not to hurt O2 sensors.   the
| Acetic Acid is what's to blame.

Perhaps, but in my brief summary of the article I left a lot in
information out. While in no way do I wish to defending this
author and his conclusions, I should at least make the following
points (at the risk of wasting network bandwidth :) ): First, it
doesn't take very high levels of silicon to contaminate the
sensor. Second, the silicon volatiles (assuming that they exist
in very small quantities) are oxidized in the combustion chamber
(introduced through the PVC system) to form smoke "containing
molecule size particles of silica (SiO2)."  Further, the author
states "when the material is on the exhaust side of the sensor,
it can be seen on the sensor shield as a fine white powder."  It
is the fine white powder, identified as silica, that poisons the
sensor by partially blocking the pores.  In essence, it acts as
a selective filter letting small molecules such as hydrogen pass
easily while larger ones such as oxygen pass not so easily.
Hence, the sensor gives a signal indicating a richer mixture.
Third, a model was sited that supports the conclusion of the
role that the silica powder plays. Fourth...  well, read the
article before you pass judgement... The authors go on to
describe screening tests used by AC for silicone rubbers to
avoid poisoning of the sensor.  (SAE article 860478, "Poisoning
of Zirconia Exhaust Oxygen Sensors by Silica", by B.W.
Holleboom, S.W. Hawes, and E.L. Ker of AC Spark Plug Div,
General Motors Corp).

                                       John S Gwynne

Oxygen Sensor Information

Written by Rick Kirchoff ( Edited to html by Kyle Hamar 

>From Fri Nov  4 12:42:39 1994

In response to several requests for more information about Oxygen (O2)
sensors, perhaps the following information will help.


     These procedures are only for self powered conventional sensors.
     Some very new cars are using a different style sensor that is
     powered.  *Many* Oxygen sensors are replaced that are good to
     excellent.  *Many* people don't know how to test them.  They
     routinely last 50,000 or more miles, and if the engine is in good
     shape, can last the life of the car.

What does the O2 sensor do?

     It is the primary measurement device for the fuel control computer
     in your car to know if the engine is too rich or too lean.  The
     O2 sensor is active anytime it is hot enough, but the computer
     only uses this information in the closed loop mode.  Closed loop
     is the operating mode where all engine control sensors including
     the Oxygen sensor are used to get best fuel economy, lowest
     emissions, and good power.

Should the O2 sensor be replaced when the sensor light comes on in
your car?

     Probably not, but you should test it to make sure it is alive and
     well.  This assumes that the light you see is simply an emissions
     service reminder light and not a failure light.  A reminder light
     is triggered by a mileage event (20-40,000 miles usually) or
     something like 2000 key start cycles.  EGR dash lights usually fall
     into the reminder category.  Consult your owners manual, auto repair
     manual, dealer, or repair shop for help on what your light means.

How do I know if my O2 sensor may be bad?

     If your car has lost several miles per gallon of fuel economy and
     the usual tune up steps do not improve it.  This *is not* a
     pointer to O2 failure, it just brings up the possibility.  Vacuum
     leaks and ignition problems are common fuel economy destroyers.
     As mentioned by others, the on board computer may also set one of
     several failure "codes".  If the computer has issued a code
     pertaining to the O2 sensor, the sensor and it's wiring should
     be tested.  Usually when the sensor is bad, the engine will show
     some loss of power, and will not seem to respond quickly.

What will damage my O2 sensor?

     Home or professional auto repairs that have used silicone gasket
     sealer that is not specifically labeled "Oxygen sensor safe",
     "Sensor safe", or something similar, if used in an area that
     is connected to the crankcase.  This includes valve covers, oil
     pan, or nearly any other gasket or seal that controls engine oil.
     Leaded fuel will ruin the O2 sensor in a short time.  If a car is
     running rich over a long period, the sensor may become plugged up
     or even destroyed.  Just shorting out the sensor output wire will
     not usually hurt the sensor.  This simply grounds the output
     voltage to zero.  Once the wiring is repaired, the circuit
     operates normally.  Undercoating, antifreeze or oil on the
     *outside* surface of the sensor can kill it.  See how does an
     Oxygen sensor work.

Will testing the O2 sensor hurt it?

     Almost always, the answer is no.  You must be careful to not
     *apply* voltage to the sensor, but measuring it's output voltage
     is not harmful.  As noted by other posters, a cheap voltmeter
     will not be accurate, but will cause no damage.  This is *not*
     true if you try to measure the resistance of the sensor.
     Resistance measurements send voltage into a circuit and check the
     amount returning.

How does an O2 sensor work?

     An Oxygen sensor is a chemical generator.  It is constantly making
     a comparison between the Oxygen inside the exhaust manifold and air
     outside the engine.  If this comparison shows little or no
     Oxygen in the exhaust manifold, a voltage is generated.  The
     output of the sensor is usually between 0 and 1.1 volts.  All
     spark combustion engines need the proper air fuel ratio to
     operate correctly.  For gasoline this is 14.7 parts of air to one
     part of fuel.  When the engine has more fuel than needed, all
     available Oxygen is consumed in the cylinder and gasses leaving
     through the exhaust contain almost no Oxygen.  This sends out a
     voltage greater than 0.45 volts.  If the engine is running lean,
     all fuel is burned, and the extra Oxygen leaves the cylinder and
     flows into the exhaust.  In this case, the sensor voltage goes
     lower than 0.45 volts.  Usually the output range seen seen is
     0.2 to 0.7 volts.

     The sensor does not begin to generate it's full output until it
     reaches about 600 degrees F.  Prior to this time the sensor is
     not conductive.  It is as if the circuit between the sensor and
     computer is not complete.  The mid point is about 0.45 volts.
     This is neither rich nor lean.  A fully warm O2 sensor *will not
     spend any time at 0.45 volts*.  In many cars, the computer sends
     out a bias voltage of 0.45 through the O2 sensor wire.  If the
     sensor is not warm, or if the circuit is not complete, the computer
     picks up a steady 0.45 volts.  Since the computer knows this is
     an "illegal" value, it judges the sensor to not be ready.  It
     remains in open loop operation, and uses all sensors except the
     O2 to determine fuel delivery.  Any time an engine is operated
     in open loop, it runs somewhat rich and makes more exhaust
     emissions.  This translates into lost power, poor fuel economy
     and air pollution.

     The O2 sensor is constantly in a state of transition between high
     and low voltage.  Manfucturers call this crossing of the 0.45
     volt mark O2 cross counts.  The higher the number of O2 cross
     counts, the better the sensor and other parts of the computer
     control system are working.  It is important to remember that the
     O2 sensor is comparing the amount of Oxygen inside and outside
     the engine.  If the outside of the sensor should become blocked,
     or coated with oil, sound insulation, undercoating or antifreeze,
     (among other things), this comparison is not possible.

How can I test my O2 sensor?

     They can be tested both in the car and out.  If you have a high
     impedence volt meter, the procedure is fairly simple.  It will
     help you to have some background on the way the sensor does
     it's job.  Read how does an O2 sensor work first.

Testing O2 sensors that are installed

     The engine must first be fully warm.  If you have a defective
     thermostat, this test may not be possible due to a minimum
     temperature required for closed loop operation.  Attach the
     positive lead of a high impedence DC voltmeter to the Oxygen
     sensor output wire.  This wire should remain attached to the
     computer.  You will have to back probe the connection or use
     a jumper wire to get access.  The negative lead should be
     attached to a good clean ground on the engine block or
     accessory bracket.  Cheap voltmeters will not give accurate
     results because they load down the circuit and absorb the
     voltage that they are attempting to measure.  A acceptable
     value is 1,000,000 ohms/volt or more on the DC voltage.
     Most (if not all) digital voltmeters meet this need.  Few
     (if any) non-powered analog (needle style) voltmeters do.
     Check the specs for your meter to find out.  Set your meter
     to look for 1 volt DC.  Many late model cars use a heated
     O2 sensor.  These have either two or three wires instead of
     one.  Heated sensors will have 12 volts on one lead, ground
     on the other, and the sensor signal on the third.  If you have
     two or three wires, use a 15 or higher volt scale on the meter
     until you know which is the sensor output wire.

     When you turn the key on, do not start the engine.  You should
     see a change in voltage on the meter in most late model cars.  If
     not, check your connections.  Next, check your leads to make sure
     you won't wrap up any wires in the belts, etc. then start the
     engine.  You should run the engine above 2000 rpm for two
     minutes to warm the O2 sensor and try to get into closed loop.
     Closed loop operation is indicated by the sensor showing several
     cross counts per second.  It may help to rev the engine between
     idle and about 3000 rpm several times.  The computer recognizes
     the sensor as hot and active once there are several cross counts.

     You are looking for voltage to go above and below 0.45 volts.
     If you see less than 0.2 and more than 0.7 volts and the value
     changes rapidly, you are through, your sensor is good.  If not,
     is it steady high (> 0.45) near 0.45 or steady low (< 0.45).
     If the voltage is near the middle, you may not be hot yet.  Run
     the engine above 2000 rpm again.  If the reading is steady low,
     add richness by partially closing the choke or adding some propane
     through the air intake.  Be very careful if you work with any
     extra gasoline, you can easily be burned or have an explosion.
     If the voltage now rises above 0.7 to 0.9, and you can change it
     at will by changing the extra fuel, the O2 sensor is usually good.

     If the voltage is steady high, create a vacuum leak.  Try pulling
     the PCV valve out of it's hose and letting air enter.  You can
     also use the power brake vacuum supply hose.  If this drives the
     voltage to 0.2 to 0.3 or less and you can control it at will by
     opening and closing the vacuum leak, the sensor is usually good.

     If you are not able to make a change either way, stop the engine,
     unhook the sensor wire from the computer harness, and reattach
     your voltmeter to the sensor output wire.  Repeat the rich and
     lean steps.  If you can't get the sensor voltage to change, and
     you have a good sensor and ground connection, try heating it once
     more.  Repeat the rich and lean steps.  If still no voltage or
     fixed voltage, you have a bad sensor.

     If you are not getting a voltage and the car has been running
     rich lately, the sensor may be carbon fouled.  It is sometimes
     possible to clean a sensor in the car.  Do this by unplugging
     the sensor harness, warming up the engine, and creating a lean
     condition at about 2000 rpm for 1 or 2 minutes.  Create a big
     enough vacuum leak so that the engine begins to slow down.
     The extra heat will clean it off if possible.  If not, it
     was dead anyway, no loss.  In either case, fix the cause of the
     rich mixture and retest.  If you don't, the new sensor will

Testing O2 sensors on the workbench.

     Use a high impedence DC voltmeter as above.  Clamp the sensor in
     a vice, or use a plier or vice-grip to hold it.  Clamp your
     negative voltmeter lead to the case, and the positive to the
     output wire.  Use a propane torch set to high and the inner blue
     flame tip to heat the fluted or perforated  area of the sensor.
     You should see a DC voltage of at least 0.6 within 20 seconds.
     If not, most likely cause is open circuit internally or lead
     fouling.  If OK so far, remove from flame.  You should see a
     drop to under 0.1 volt within 4 seconds.  If not likely silicone
     fouled.  If still OK, heat for two full minutes and watch for
     drops in voltage.  Sometimes, the internal connections will open
     up under heat.  This is the same a loose wire and is a failure.
     If the sensor is OK at this point, and will switch from high to
     low quickly as you move the flame, the sensor is good.  Bear in
     mind that good or bad is relative, with port fuel injection
     needing faster information than carbureted systems.

     ANY O2 sensor that will generate 0.9 volts or more when heated,
     show 0.1 volts or less within one second of flame removal, AND
     pass the two minute heat test is good regardless of age.  When
     replacing a sensor, don't miss the opportunity to use the test
     above on the replacement.  This will calibrate your evaluation
     skills and save you money in the future.  There is almost always
     *no* benefit in replacing an oxygen sensor that will pass the
     test in the first line of this paragraph.

Rick Kirchhof   Austin, Texas                   | Experience is what you
Domain:                   | get when you don't
Bang path: ...!!peyote!posms!rick  | get what you want.


X-Source: The Hotrod Mailing list
From: emory!!xgg3511 (Roger Hensley)
Date: Thu Sep  9 19:12:41 1993
Subject: Air / Fuel Guage results & Thanks.

Just a word to say thanks to all those people that helped us out on our
Air/Fuel meter question I posted a few weeks ago. We bought a couple of
Cyberdyne Air/Fuel Gauges from SUMMIT for $30.99 and installed a BOSCH O2
sensors at each collector on my friends (Andy) Datsun 240Z SCCA ITS race car.

During warm ups at Grattan raceway on 04 September both gauges read two bars
too rich (what ever two bars mean). The car was brought in and the carbs
leaned out. Back on the track the gauges read center or stoch. and Andy's
times improved down the straight and throughout the course. Saturday Andy
qualified second in class behind a 280Z. On Sunday the gauges were still
reading stoch and Andy won the South Bend regional race being chased by the
280Z. On Monday he qualified for the Western Michigan regional races 3rd
overall and 1st in class in the rain. The Cyberdynes were now reading two bars
too lean; however, we did not readjust the carbs because the race was
scheduled to be run later in the day and the forcast was for clear skies. I
figure the cooler temps were making the air a little denser thus the reason
for the lean condition. The guess was correct. During the race the skies were
clear and temp was warming up to what it had been Saturday and Sunday. Andy
won the Monday race again being chased by the 280Z.

We learned a lot using the Cyberdynes. They aren't perfect but do  give an
adequate indication of what is going on. By the way we used 75% HI OCTANE
unleaded fuel and 25% leaded Racing Fuel. It didn't seem to bother the O2
sensors. Anyway Thanks a Bunch!

Roger Hensley
Patriot Motorsports

[The guys down at Ga Tech F-SAE team have been using lambda sensors with
leaded fuel for quite some time.  They were fortunate to have had GM
donate a whole box full of sensors to the effort.  They tell me the sensor
will last for a few hours of dyno running.  The first indication
of poisoning is sluggish response.  Sounds like yours should be good
for a couple of events.  JGD]

Date: Mon Oct 11 23:39:00 1993
Subject: Re: custom O2 gague (& others)
X-Source: The Hotrod Mailing list

   In message  , you write:

|   these questions deal with the air/fuel mix sensor (like cyberdyne's
| in the summit catalog):
|  - where does the sensor need to be located, ie real close to the
|    engine (reporting on just one cylinder (and hoping it is
|    'typical')), or can it be put down on the collector, so it would
|    report on how the cylinders (as a whole) are doing?
|  - how does the placement affect the accuracy/linearity (or what else?)

Sensor location is important for the non-heated EGO sensor. Too close
to the engine and it will become too hot and shorten the life
expectancy. Too far way and the sensor may not stay warm enough to
work at idle.  Location is not a problem for the thick film heated
sensors (TFHEGO), and placement in the collector is fine.

|  - does the sensor come with a full spec sheet (ie what the voltage or
|    resistance is for different a/f ratios, or can one be obtained?
|   which leads me to the thought that brought on the questions: i want
| to make a small 'gage' for a/f ratios (i don't like the look of the
| cyberdyne unit), with 5 lights or led's on it:
|    1) red    -> way too lean
|    2) yellow -> fuel-economy cruise (slightly lean)
|    3) green  -> stoich
|    4) yellow -> acceleration (slightly rich)
|    5) red    -> way too rich

As far as I know (which may not be much :) ), all of these gauges for
under $150 that claim to cover such a wide A/F range (specifically on
the rich side) ARE bullshit...  I bought the Edelbrock air/fuel
monitor (see post end of March/93 in the archives --
and traced out the circuit. It uses a TFHEGO in the voltage
generation mode which can really only indicate 2-states (rich/lean).
Needless to say that I was not happy and you should not waste your
money on that one....  Before you buy one of these, run down to that
auto parts store and get a generic 3-wire sensor.

To build a wide-range Air/Fuel meter, you need something like a UEGO
sensor (again see the archives) that would use a oxygen cramming
method or oxygen bias method (see SAE journals). This can cover the
range .6

Date: Tue Jul  5 13:15:15 1994
Subject: Honda LAF sensor
From: emory!!dave.williams (Dave Williams)
X-Source: The Hotrod Mailing list

 The wide-range O2 sensor used in some of the Hondas is called an LAF
sensor in England, UEGO over here.  There's a chart in the October 1991
Car Design & Technology which shows the response curves of a
conventional Lambda O2 sensor and the Honda LAF sensor

 The LAF's response isn't linear, as depicted on the chart.  It starts
at about -5v at 10:1 A/F, moving up sharply to about -1v at stoich, then
progressing slowly up to maybe +2v at 25:1.

Date: Fri Nov 11 01:36:58 1994

Almost forgot.  On the Grand Nationals the usual recommendation is to tune
for an O2 volts of 0.76-0.78 V at wide-open throttle.  Over .8 is too rich
and less than .74 is just starting to knock (according to the knock sensor,
anyway).  I know that there is some variation from car to car, but I don't
know how large it is.  Ken Mosher has the most experience with this, and he
has gone through at least 6 O2 sensors in several seasons of racing with
leaded race gas and he has always recommended .76-.78 V, so the variation
can't be greater than .02-.04 V from sensor to sensor.  If you mount the
sensor in the header collectors on a V8 I would strongly recommend a heated
(3-wire) sensor so it doesn't cool off at idle.  Good luck.


Carl Ijames

From: (Larry Piekarski)
Subject: Re: New Question (was Re: Determining AFR...)

> Second Question:
> If the above is true, how would I go about wiring up one of these bar graphs
> from radio shack, as to not short anything out, or ruin any of my current
> wiring?  (i.e. what resistors, etc. would I need for this readout)
> I'm not much of a circuit builder -but am trying to learn.

First, the O2 sensor is extremely high impedience, 22 MOhm. If you are
building a readout device, make sure you start with a very high impedience
voltage follower.
Second, most voltmeters and scopes have only 1 MOhm inputs, so be cautious
of the readings you get.

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