924Board.org

[eturbo924]

Quick question here. If I put a multi-meter on the line to the O2 Sensor I shuld see some current correct? Between 0-1 volt depending on the fuel mixture right? So if no voltage even if I put the multi meter to a ground would mean a bad line to the O2 correct.... or am I missing some thing?

Thanks

Eric

[awilson40]

First, disconnect the sensor from the circuit. Then when the sensor is warmed up it should put out between .3-.8 volts depending on the mixture.
A good way to test is remove the sensor, hook up a dvm, pos to lead, neg to case and heat with a propane torch. Once red hot, you should get around 800 mv, rapidly dropping when the flame is removed and rapidly rising when the flame is returned.

[wdb]

I believe the o2 sensor acts like a thermocouple , the probe itself generates the milivolts and sends the current down the line . if the wires are disconnected from the o2 sensor there will not be any current in the wires

[Diesel]

[awilson40]

Or a photo cell...instead of light, its the difference in O2 content that creates the differenve in potential I.E. Voltage
But the sensor has to be up to temperature befor it will work. Some sensors have 3 wires, one being power for a heater.

[eturbo924]

Ok I will check it again. Maybe it was not warm enough at the time. I was just checking for any reading in the line and got nothing. I spliced in a line for the Muti-meter and saw no reading maybe the O2 sensor was not up to temperature yet. I will try again tonight .

Thanks guys

Eric

[eturbo924]

Ok guys I tested it again last night. I could still not get any signal from the O2 sensor. I did not remove it though. Let the car run for some time to warm it up. Then I put the probes of the Multi meter into the line from the Sensor and nothing. So then I played with a few things to try to get anything. Then I decided to try to put the meter in series with the O2 sensor so I unplugged the O2 and ..... hmmmmm the engine just jumped about 200 rpms. Weird.... so I decided to try driving the car with the O2 unplugged. WOW!!! What a difference! Car is now about 97% of what I expected. I am sure the fuel mixture is still off but it is much much better in the low rpms. No more bogging and then surging at 3200rpms. So any one want to guess what the issue is? Obvioulsy there is a signal coming from the O2 or maybe there is a short that is grounding through it and when it is unplugged ..... Anyway she is much better but I bet the gas mileage will go down. I used to run it this way all the time with decent results... my mechanic set it and unplugged the O2.

Eri

[John Brown]

First: these cars run just fine with the sensor unplugged, thank you very much! So if emissions inspections are not an issue leave well enough alone.

Second: been bothered much by your reference to 'multimeter'. Often people use the term 'mulitmeter' when talking about an inexpensive and LOW IMPEDANCE device. Not suitable for measuring things like O2 sensors as they are voltage (high impedance) devices and cannot supply current. So the meter loads down the device and the measurement is invalid.

Third: when inserted in series the operating voltage of the meter supplied the signal to the lambda control unit.

Question: Do you have the wiring diagram for the car? Are the throttle switches all set correctly? Is the mixture set? What about the ouput on the test lead provided? (small 3 conductor plug in the vicinity of the charcol cannister vacumn control valve)

[eturbo924]

Been bothered? Sorry not meant to bother.
I had a nice multi meter but it died and I did not feel like paying $200 again at the moment... so you are correct in assuming I am using a "volt meter". If this will not properly measure the O2 then just say so.

The switches are in proper position and wired properly. They seem to function also... when checked electrically for continuety (sp?) Yes I have the wire diagram.

Mixture may or may not be perfect. I do not have "the proper" instrument any longer to check. Best I can do is use the O2 with a new meter (if I pop for one) or give it to my mechanic... or do the set by ear thing.

Car does run great now with out the O2 so I might just leave it and play with the timing now. It does not need to be a rocket just wanted to be rid of the hesitation... I did and thus I am happy.

Thanks for the input. I will be more careful to use the correct terminology.

Eric

[wdb]

[awilson40]

I know mine wont run well with it disconnected. Even if I adj the idle mixture to compendsate.I read somewhere that the fuel distributor is different on Lambda cars. A different fuel flow rate and curve to allow the Freq valve to have room to compensate.

[924 turbo]

When I bought my '80 924, the O2 sensor was disconnected. It ran well disconnected, and I even passed California smog without it (albeit with a new catalytic converter). With the sensor connected, it runs just about the same. Of course, the car is at full throttle an awful lot.

[Paul]

From:

http://www.birrabrothers.com/tiger/e36/docs/all_o2sensor.htm

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.

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.

--





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.




[ This Message was edited by: Paul on 2002-08-11 11:40 ]