Oxygen Sensor Information

Written by Rick Kirchoff (rick@posms.cactus.org). Edited to html by Kyle
Hamar

>From Terrill_Yuhas@smtpsc1.sc.pima.gov 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.

Comment:

     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
     fail.

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: rick@posms.cactus.org                   | get when you don't
Bang path: ...!cs.utexas.edu!peyote!posms!rick  | get what you want.

===========================================================================

>From hotrod@Dixie.Com Tue Mar 30 11:11:25 1993
Subject: Edelbrock air/fuel ratio monitor
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 4717
X-Archives: ece.rutgers.edu

Well....

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
   jsg@magnus.acs.ohio-state.edu

----------
Posted by: John S Gwynne

>From hotrod@Dixie.Com Thu Apr  1 12:39:23 1993
Subject: Re: Edelbrock air/fuel ration monitor
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 4777
X-Archives: ece.rutgers.edu

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
one.

[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 ece.rutgers.edu
JGD]

John S. Gwynne
   jgwynne@magnus.acs.ohio-state.edu

----------
Posted by: John S Gwynne

>From hotrod@Dixie.Com Mon Jul 26 12:46:06 1993
Subject: Re: More about Holleys
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 5884
X-Archives: ece.rutgers.edu

> O2 Sensor setup, etc <

 I drilled a hole in the cast iron exhaust manifold right before the outlet
flange, and reamed it out until an 18mm anti-fouling spark plug adaptor was
a hammer fit. I ground down the adaptor until its inner end was flush with
the interior wall of the manifold, and then welded it in place.

 The O2 sensor I used was a freebie 1-wire type. A 3-wire is better for
reasons I'll go into in a bit, but costs more. I picked up ground locally
using a valve cover bolt through a loop soldered in the end of the ground
wire, and connected the O2 sensor to its mate, solder and shrink-wrap.
I used some automotive "trailer wire" (the 4-conductor ribbon used for
hooking up auxiliary lights etc.) which seems to be taking the heat
and grease reasonably well. The reason for taking a local (engine block)
ground is to minimize any error induced by body/block return currents
and any voltage offset that might develop from loads like A/C, lights
if you used the dash as ground.

 I am using a spare analog VOM to read O2 volts; it seems to be working
well enough, even though I've been told that the O2 sensor needs a very
high load impedance. This meter has about 100Kohms (50K/volt, 2.5V scale)
and I think it's about on the edge of affecting the sensor output
accuracy; if I switch to the next lower scale I get a slightly lower
value reading indicating Zload sensitivity to me.

 The reading ranges from 0 to 1V (approx), with 0 indicating lean and 1V
indicating rich. 0.5 is supposed to be stoichemetric. When warm I seem
to be pegged rich, or close to it, except for a "hole" during throttle
transitions.

 The one-wire sensor depends on exhaust heat to activate it; the element
has to be pretty hot to develop any voltage and low temperatures result
in a reduction or absence of output. I find that there's not enough heat
at idle to keep the sensor fired up. If I idle for more than a few seconds
the output voltage starts to decay. The other thing is that it takes a
while to start reading. For a tailpipe test rig I made, a 3-wire was a
necessity since by that point there's not enough heat ever.

 For a permanent installation I think the best solution would be to use
a small panel meter with a single-supply op amp as a unity gain buffer
and a calibration resistor to get 1V full scale. A shunt resistor from
amplifier output to ground might help the amp in the low end. I tried
cobbling up a bar graph display using an old LM3914 I had in the parts-
is-parts tin but it seems to have developed an attitude. For some
reason Radio Shack has stopped selling these although they still sell the
bar graph displays.

----------
Posted by: emory!mlb.semi.harris.com!jws (James W. Swonger)

>From hotrod@Dixie.Com Mon Aug 16 21:12:16 1993
Subject: 02 sensor help!
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 6040
X-Archives: ece.rutgers.edu

> O2 Sensor setup, etc <

.....

>The O2 sensor I used was a freebie 1-wire type. A 3-wire is better for
reasons I'll go into in a bit, but costs more.

We are interested in putting an 02 sensor in a Datsun 240Z SCCA ITS class
road race car. The Datsun has a six into two header (where three cylinders
being fed by one carburetor) into a dual exhaust system. We are interested in
monitoring the air / fuel ratio of each carb (3 cylinders) while the car is at
speed to determine efficiency at high RPM.

We understand K & N makes an air/fuel monitor that retails for $139.00. Can we
inexpensively duplicate this device or do you have a better, less expensive
alternative.

Also, does the 02 sensor develop its own voltage or is it a variable
resistance device? Any explanation (reference material, etc.) on how this
operates would be greatly appreciated.

Roger Hensley
Patriot Motorsports
1099 N. 16th St.
Otsego, Mi 49078

[Cyberdyne makes an in-dash A/F indicator that lists for $29 in Summit's
catalog.  Don't pay a dime more.  Many of these things are labeled with
wide range A/F ratios.  Since the standard O2 sensor covers a narrow range
around stoich, this labeling is fraudulent.  As long as standard production
O2 sensors are used (UEGOs sensors by themselves cost several hundred bux),
all the displays must work the same.  If you want an analog readout,
a simple analog meter with an op-amp buffer does the trick.  the voltage
range from the sensor is 0-1 volt at high impedance so gain isn't necessary;
only buffering.

For references, see the archives plus SAE's "Sensors and Actuators"
publication from the last few years.  More info than you can stand.
Remember though, lead-free gas only.  JGD]
----------
Posted by: emory!dcmdc.dla.mil!xgg3511 (Roger Hensley)

>From hotrod@Dixie.Com Thu Sep  9 19:12:41 1993
Subject: Air / Fuel Guage results & Thanks.
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 6309
X-Archives: ece.rutgers.edu

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]

----------
Posted by: emory!dcmdc.dla.mil!xgg3511 (Roger Hensley)

>From hotrod@Dixie.Com Mon Oct 11 23:39:00 1993
Subject: Re: custom O2 gague (& others)
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 6678
X-Archives: ece.rutgers.edu

--------

   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 -- ece.rutgers.edu)
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

>From hotrod@Dixie.Com Tue Jul  5 13:15:15 1994
Subject: Honda LAF sensor
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 8868
X-Archives: ece.rutgers.edu
X-Comment: Send subscription and drop requests to hotrod-request@dixie.com
X-Comment: Send comments and trouble reports to jgd@dixie.com

 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.

----------
Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)

>From KEN_MOSHER@gmgate.IMD.Sterling.COM Tue Apr 20 15:21:53 1993
Date:    20 Apr 1993 15:18:26 U
Subject: Injectors
From:    "KEN MOSHER"

                          SUBJECT:  Injectors
I ran across the following information about injectors and thought it may be of
general interest:

Manufacturer        Part #        Flow @ 45 psi
================================================
Lucas              5208006         15.8 lbs/hr
Lucas              5207011         23.9 lbs/hr
Bosch (Stock GN)   0-280-150-218   29.8 lbs/hr
Bosch (Supercoupe) 0-280-150-756   32.0 lbs/hr
Bosch (Porsche)    0-280-150-213   33.0 lbs/hr
Bosch              0-280-150-911   33.0 lbs/hr
Lucas              5207009         33.2 lbs/hr
Lucas              5207008         40.1 lbs/hr
Bosch              0-280-150-803   40.0 lbs/hr
Lucas              5107010         52.0 lbs/hr
AC Rochester       MSD 2014        72.0 lbs/hr
Bendix (red)       GM25500139      82.0 lbs/hr
AC Rochester       MSD 2015        96.0 lbs/hr
Bendix (white)     GM (alcohol)   180.0 lbs/hr

This data was gathered from ATR's literature enclosed in their 7th injector
kit.  Also, they note that the rated flow is NOT at rail pressure.  The value
at 45 psi is the differential pressure across the injector.  In other words, if
the fuel pressure is 65 psi @ WOT and the boost is set at 20 psi, the
differential pressure is 45 psi.

They also included an A/F ratio graph that confirmed what I saw on the chassis
dyno with my car ... namely that under boost the car should hover around 12.5:1
for best HP and detonation resistance.  A crude ASCII rendering of the graph is
below:
___
   |         ! *******    !       !       !        !
   |         **        ******     !       !        !
   |      *  !            !  *****!       !        !
BHP|    *    !            !       **      !        !
   |  *      !            !       ! **    !        !
   |*        !            !       !   **  !        !
___|         !            !       !      *!        !
   |  RICH   !  CORRECT   !  LEAN ! LIGHT !* SEVERE!
   |         !    A/F     !       ! KNOCK ! *KNOCK !
   |         !            !       !       !  *     !
   |         !            !       !       !   *    !
   |         !            !       !       !    *   !
   |         !            !       !       !     *  !
   |         !            !       !       !      * !
___|_________|____________|_______|_______|________|
   |         |            |       |       |        |
  11.0      12.0         13.0    13.5    14.0     14.7
                      Air/Fuel Ratio

-- Ken Mosher
-- Buick Grand National:  More *POWER*!  More *BOOST*!  Urrrrr! Urrrrr!

>From ijames@codon.nih.gov 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.

Regards,

Carl Ijames     ijames@codon.nih.gov

From: jws@billy.mlb.semi.harris.com (James W. Swonger)
Subject: Re: Determining AFR from O2 Voltage readout

 A non-heated sensor will behave as described if driving a low
impedance load. This is due to the low exhaust temperature at
idle, which reduces the current available from the cell. There
will be an error induced, which is less into a higher impedance
DVM than a resistive input such as a VOM (I have used both and
observed this directly). The bargraph indicator may have an
input resistance low enough to make this noticeable. On my
van, I could see the sensor output voltage indication drift
downward at about 100mV/sec after dropping onto idle. Eventually
it would hit the floor, just "go out". Revving it for a few
seconds would light it back up, and cruise was enough to keep
it hot. With a very high input impedance meter, the indication
remains steady even at idle.

 You can substitute a heated sensor to get around the problem
of inadequate exhaust temperature; three wire Bosch sensors
can be gotten cheap at the AutoZone or whatever, if the
future high school graduate behind the counter can be made
to understand the concept of reading a parts list. I used a
heated generic sensor to make a slip-on tailpipe sniffer.

 You could also try using header wrap to maintain exhaust
temperature up to the point where the sensor is located.

From:

     Steve, I saw your post on rec.autos..... and thought I'd lend you my
     ?.02.  Somone on the Corvete mialing list had a similar type of
     question, so I thought I'd just copy the note over to you too.  If you
     have any questions, EMAIL me.  For some reason I can't post to
     rec.autos.

     Standard O2 sensors basically measure rich or lean operation.  Their
     response is very nonlinear and can not be used to measure precise A/F.
      In computer controlled cars, the computer operates on a limit cycle,
     switching between rich and lean in order to average out to a
     particular A/F (usually stoich.).  Sensors to measure actual A/F and
     not just rich/lean do exist, they are called Universal Exhaust Gas
     Oxygen sensors (UEGO) or Linear EGO sensors.  Essentially a UEGO
     sensor is two EGO sensors physically linked.  One half of the sensor
     is exposed to exhaust gas, the other to O2.  To make a long, complex
     story short,  just as O2 causes a potential difference across the
     walls of the O2 sensor, pumping current into the O2 sensor can cause
     O2 ions to flow through the sensor.  By measuring how much current
     must be pumped into the sensor in order to maintain a constant voltage
     across the O2 detecting cell (450 mV), the A/F can be determined.
     These devices are common place in dyno/engine calibration labs (at
     least here at Motorola and at Ford).  The interface circuit for the
     sensor is extremely complex, as the sensor must be maintained in a
     closed loop and the currents measured are very small (into the tens of
     uA's).  Besides having to control the O2 detecting and pumping cells,
     the heater must also be controlled and maintained at 10V RMS, battery
     voltage will burn it out.  However, battery voltage (actually 12V
     RMS)is used to quickly warm up the sensor, after which the heater
     voltage is reduced.  Thus, another circuit is used to detect when the
     sensor is warm.  If current is pumped into a cold sensor, it will
     "blacken" and be destroyed.  Operating temperature of the sensor is
     determined by measuring its electrical impedance.

     I worked on such a circuit for Ford a few years back with the
     intention of putting it into production vehicles.  It turned out that
     it was not cost effective for the benefits (at least that was their
     reason for killing the project).  Instrumentation sensors like this
     exist, along with their digital readout, but they cost about ?8K! NTK
     (a division of NDK Spark Plug) is a very popular one.

     I think that it would be possible to make a crude A/F meter using a
     standard ZrO2 EGO sensor and measuring the time that is spent lean (<
     450mV) vs. rich (> 450mV).  Note that nearly all (if not all) EGO
     sensors are actually HEGO sensors, H for heated.  With these standard
     O2 sensors, battery to the heating element is sufficient.

     Hi Steve.  You asked:

     " If an AFR sensor is basically two EGO sensors (one on the inside of
     the exhaust manifold, and one on the outside), and the two compare
     readings, I don't see why it would
     be so hard (so expensive) to make a device to do this.  Probably the
     circuitry in determining the AFR from the comparison of inside/outside
     voltages I guess."

     They are not two separate sensors.  As a simplification, you can think
     of them as two separate sensors, but they are physically linked so
     that the O2 ions can flow from one side to the other.  The O2
     reference is created by applying a very small bias current to the
     sensor.  This creates an O2 reference in part of the cell.  It is not
     exposed to outside air, however.

     I will keep an eye peeled for your summary post.

(here it is Mark ;-)

Mark Stavropoulos
Motorola AIEG
Northbrook, IL
g10137@email.mot.com

>From sorlin@magnus.acs.ohio-state.edu Sat Nov 12 20:49:30 EST 1994

In article <1ad.2720.1765@uchoice.com>,
John Avery  wrote:

>The November 1994 issue of SEMA News (Specialty Equipment Marketing
>Association) shows the folowing "tuning aid" as they call it:
>Accell...introduction of a new air/fuel ratio meter for all automotive
>and light-truck applications. The new product is a tremendous tuning aid
>for enthusiasts with both carbureted and fuel-injected engines. The
>meter allows the driver to the monitor the air/fuel ratio during actual
>operating conditions and is driven by a fast response oxygen sensor that
>is bolted into the exhaust system. Close calibration of fuel curves
>becomes quite easy, allowing precise fuel metering at all engine
>speeds." The address is:
>Accel
>8700 Brookpark Rd.
>Cleveland, OH 44129
>(216) 398-8300
>I have nothing to do with this company. I just thought it was relevant
>to this thread. Hope it helps somebody.

It definitely is.  Before I started this thread, I knew very little about
O2 sensors, and was hoping that I could use one to determine exact AFR
in my engine.   Since then, I have received much information from everyone
(thanks everyone!) and have learned quite a bit about O2 sensors.  Still would
like to know more though.

I'm going to repost with all the info I have received in a few days, maybe
somebody with some more disk space would like to keep all the info as
FAQ material?

Anyways, from the descriptions of how O2 sensors work, and operate in a closed
loop system, it appears obvious to me know that all a regular O2 sensor
can do is sense rich or lean conditions with reference to the stoich mixture
of 14.7:1   In fact, that is all it NEEDS to do to keep a closed loop system
working well, since in closed loop, the computer wants the mixture to
stay as close to stoich as possible (the rich and lean voltage indications
of the O2 sensor just keep bouncing signals back to the computer, which
in turn keep the mixture very close to 14.7:1)

>From the many descriptions, and opinions I have received, there is NO steady
relationship (linear, cubic, quadratic, etc.) between the O2 sensor voltage
and the AFR.   Therefor, from many others conclusions, I have come to the
conclusion that no products which offer an AFR from a regular O2 sensor
can even be the least bit accurate in determining a numerical AFR.

On the other hand, a system like MSD's which only indicates rich/lean is
plenty accurate, because that information CAN be obtained from the O2 sensor.
Whether it is worth $150 is up to the owner, seeing as how the same readings
can be obtained by a regular O2 sensor and a good voltmeter.

According to the information I have received, only a UEGO  (Universal exhaust
gas oxygen) sensor can determine accurate AFR readings.   I won't go into
how one of these gems works right now, it will be in the repost.
Also, according to the information I have received, these sensors cost a LOT
of money, and the interface circuitry is extremely complex and expensive.

So, that's pretty much where it is left with me,   any product which works
off of a regular O2 sensor and claims to measure AFR is a scam.
And the products which actually can measure AFR cost a pretty penny.

This is NOT to say that the regular O2 sensor can't be used for tuning.
Because it can be very helpful for tuning for emissions, or returning an engine
to a previous mixture setting (which you had recorded in O2 sensor volts).

So in conclusion, I would like to know how Accel's unit operates.  Does it
operate off of a regular O2 sensor, or a UEGO sensor?  (rhetorical question -
unless someone has the answer)

Steve

From: pi@c1ilep.delcoelect.com (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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