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Testing Jeep O2, Oxygen sensors

Not much experience with the Renix O2 sensor. I had a problem with my 4.0, but it was an open O2 heater circuit, found using an ohm meter.
The digital VOM works fine for testing the HO O2 sensors (they're the same as GM units). The last high impedance analog volt meter I had access to, besides an o-scope, was a vacuum tube VOM;). I find it hard to beat the accuracy of the digital meter, especially when you take into consideration parallax and meter movement error.


My analog has 2 zero knobs, one for volts, another for ohms, that you use to calibrate the meter before each test (compensates for battery age), and it has a silver mirror behind the neddle for eliminating the parallax error. But you are right concerning cheaper design analog meters. I have found digitals to be error prone just before the battery dies, just like analogs.
 
Have you run across a similar testing procedure for HEGO units akin to our RENIX ones?

See my first 2 posts, first one for Renix, the other for HOs. I got tired of posting it weekly here in a thousand threads, so I gave it a thread with an easy to find title and you still missed it!:rattle:

LOL. :D

xjbubba,

I might add that the bench test you described could be run by hot wiring the O2 heater wires to a 12 volt car battery (make damn sure you know which wires folks, or you might fry the O2 sensor), then all you need is to vary the O2 concentration locally, using say propane, or nitrogen gas. Nitrogen, if available would be safer. CO2 gas should work too.
 
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Is it using a lot of oil? You might try disconnecting the O2 sensor to see if mileage drops further. A bad O2 sensor seems to waist about 6 mpgs of gas on our rigs. If the mileage is unchanged in a tank of gas with no O2 sensor connected, then your MPG problem is at least partly an O2 sensor problem. But you need to find out if it is the sensor, bad wiring (all too common, they tend to get intimate with exhaust pipes, the wires), or a bad ECU, or cracked Ex-manifold.....before buying a new sensor.


Interesting rig you found there. Certainly priced right. I wonder if it would test the CPS too?

On my XJ, if the primary O2 sensor is disconnected the engine will not run past the initial 5 minutes after a cold startup. It must be connected and be working reasonably well. Also a bad O2 sensor causes the engine to stumble at highway speed and shut down on the city streets. It will restart after about 15 minutes and run for another 5 minutes. The sensor in the cat triggers the check engine light but that is all.
 
In response to Ecomike's comment stating my testing procedure is in error regarding the output of an O2 sensor with the key on/engine off, I'll stand by my "guidance". Now, first, I stated in another post that I had minimal experience with Renix O2 sensors, but was referring to Jeep HO and similar O2 sensors (like the ones GM has been using since the mid '80s); I've had extensive experience testing the more common sensors. When you back probe the sensor output lead, and turn the key to "ign", you are looking at the ECM generated reference voltage--not the O2's output. Obviously, with engine not running, there will be no output.
If you read "0" volts in this circumstance, as Ecomike suggests you should, that would indicate a problem with either the wire, or with the ECM. That's why it's a good first step in testing the ECM circuit.
And, no, it's not necessary (or recommended by me) to pull the O2 sensor out of the exhaust to test it; however, if you have a couple of sensors laying about, for whatever reason, it's easier to "bench" test them than to install them in the exhaust just for that purpose.
I don't care what kind of meter you want to use for testing electronic circuitry, it should be high impedance. For testing low-end devices, like resistors, capacitors, transformers, most any analog multimeter will work, and for some cases, as previously discussed (the TPS for example), the analog meter is preferred. That said, the analog meter requires more interpretive skills than a digital meter to use correctly and accurately; also the meter is most accurate in the upper 1/3rd of the select range. There are no issues with parallax or meter movement error to consider with the digital multi-meter. The problem with the digital meter is that it uses circuits to convert from analog to digital, requiring it to sample detected voltage at some predetermined rate (such as to times per second). I might add that anytime you're using a scanner to look at engine sensor data, the operation is the same as using a digital meter; the ECM is converting the sensor data to digital and sampling the converted data at some predetermined rate. This sampling requirement reduces the digital meters effectiveness in testing varying DC voltage, or varying resistive values, such as seen when testing a TPS for discontinuity (bad spots); a relevant reading may be lost between samples.
As far as high or low impedance goes, most people in the business would call 40k ohm/volt low impedance. Testing an O2 on the 3-volt range would be the same as putting 120k resistor in parallel with the sensor--not good. The digital meter (the common variety most of us have) is like placing a 10 meg-ohm resistor in parallel. With the circuits we test (automobile ECM/PCMs), 10 meg-ohms will not affect the readings in a material way.
The best I can tell searching for info on the E-bay meter you sited as using over the last 35 years, the Micronta 22-210, the unit is a 30k ohm/volt multimeter--not good, in my opinion, for testing active electronic circuits or components: "22-210 30,000 OHMS/VOLT MULTITESTER".
With regard to using nitrogen or CO2, neither will accomplish the objective of richening the mixture to test O2 response. Since the test I described required the engine to be running, the O2 heater circuit should also be active, by default.
 
In response to Ecomike's comment stating my testing procedure is in error regarding the output of an O2 sensor with the key on/engine off, I'll stand by my "guidance". Now, first, I stated in another post that I had minimal experience with Renix O2 sensors, but was referring to Jeep HO and similar O2 sensors (like the ones GM has been using since the mid '80s); I've had extensive experience testing the more common sensors. When you back probe the sensor output lead, and turn the key to "ign", you are looking at the ECM generated reference voltage--not the O2's output. Obviously, with engine not running, there will be no output.
If you read "0" volts in this circumstance, as Ecomike suggests you should, that would indicate a problem with either the wire, or with the ECM. That's why it's a good first step in testing the ECM circuit.
And, no, it's not necessary (or recommended by me) to pull the O2 sensor out of the exhaust to test it; however, if you have a couple of sensors laying about, for whatever reason, it's easier to "bench" test them than to install them in the exhaust just for that purpose.
I don't care what kind of meter you want to use for testing electronic circuitry, it should be high impedance. For testing low-end devices, like resistors, capacitors, transformers, most any analog multimeter will work, and for some cases, as previously discussed (the TPS for example), the analog meter is preferred. That said, the analog meter requires more interpretive skills than a digital meter to use correctly and accurately; also the meter is most accurate in the upper 1/3rd of the select range. There are no issues with parallax or meter movement error to consider with the digital multi-meter. The problem with the digital meter is that it uses circuits to convert from analog to digital, requiring it to sample detected voltage at some predetermined rate (such as to times per second). I might add that anytime you're using a scanner to look at engine sensor data, the operation is the same as using a digital meter; the ECM is converting the sensor data to digital and sampling the converted data at some predetermined rate. This sampling requirement reduces the digital meters effectiveness in testing varying DC voltage, or varying resistive values, such as seen when testing a TPS for discontinuity (bad spots); a relevant reading may be lost between samples.
As far as high or low impedance goes, most people in the business would call 40k ohm/volt low impedance. Testing an O2 on the 3-volt range would be the same as putting 120k resistor in parallel with the sensor--not good. The digital meter (the common variety most of us have) is like placing a 10 meg-ohm resistor in parallel. With the circuits we test (automobile ECM/PCMs), 10 meg-ohms will not affect the readings in a material way.
The best I can tell searching for info on the E-bay meter you sited as using over the last 35 years, the Micronta 22-210, the unit is a 30k ohm/volt multimeter--not good, in my opinion, for testing active electronic circuits or components: "22-210 30,000 OHMS/VOLT MULTITESTER".
With regard to using nitrogen or CO2, neither will accomplish the objective of richening the mixture to test O2 response. Since the test I described required the engine to be running, the O2 heater circuit should also be active, by default.

Two comments or questions, one, do you have a link to the .45V reference voltage on the ECM (PCM) reference voltage to the O2 sensor on the HO models with power on, run mode, but engine off? Or is this just your own test data. Either way is it the same for OBD-I and OBD-II years? I find it a little strange they would supply a test volatge in the that mode, but pehaps they had pre test reasons.

Second, the CO2 / nitrogen comment was for bench testing, not live in the running engine testing. Sorry if I was clear on that.
 
FSM says the Renix O2 sensor operating temperature is "1475 F (850 C)".
 
I don't have specific sites for the Jeep HO engine PCM, but do have sites for the use of the .450v for fuel injection control systems using the zirconia oxygen sensor. This is the sensor type used to control air/fuel mixture in the 90 up Jeep, and many other vehicles.
Besides the sites I pasted below, I quote page 3-10 from my 1994 C/K (GM) truck driveability, emissions and electrical diagnosis manual: "--The control module puts out a reference signal of 0.45 volt (450mV). The reference signal serves two purposes. The first is to run the engine when it is in "open loop" mode of operation.---" It then goes on to explain "closed loop" operation, and the use of the reference signal to control the air/fuel mixture.
I know this info is valid for OBD-I Jeeps and GM trucks/cars, and I believe many OBD-II vehicles, who are using zirconia sensors, also follow similar practice with regard to the .450v reference signal.

Info relative to Renix O2 sensors:

http://www.dnd-automotive.com/tuneup/02-sensor.htm
Some vehicles are equipped with a different type of O2 sensor that has a titania rather than zirconia element. Instead of generating its own voltage signal, a titania O2 sensor changes resistance as the air/fuel ratio goes from rich to lean. Instead of a gradual change, it switches from low resistance (less than 1,000 ohms) when the mixture is rich, to high resistance (over 20,000 ohms) when the mixture is lean.
The engine computer supplies a base reference voltage of approximately one volt to the titania O2 sensor, and then reads the voltage flowing through the sensor to monitor the air/fuel ratio.
When the fuel mixture is rich, resistance in a titania sensor will be low so the voltage signal will be high (close to 1.0 volt). When the fuel mixture is lean, resistance increases and the voltage signal drops down to about 0.1 volt.
Compared to the more common zirconia O2 sensors, titania sensors have three advantages: (1) they don't need an air reference (there is no internal venting to the outside atmosphere to plug up); (2) they have a fast warm-up time (about 15 seconds); and (3) they work at lower exhaust temperatures (they won't cool off at idle and they can be located further downstream from the engine or used with turbochargers).
Chrysler also uses them on the Jeep Cherokee and Wrangler (because of the sensor's ability to handle off-road driving through water), and the Eagle Summit.

Info relative to the standard zirconia (as in '90 up Cherokee) sensor

http://www.brakeandfrontend.com/Article/38744/Oxygen_Sen.aspx


Based on the oxygen sensor voltage, the controller will increase or decrease the pulse width of the injector, which in turn will change the oxygen sensor voltage for the next injector pulse. The oxygen sensor is also referred to as a lambda (l) 1 sensor. Lambda is the Greek letter equivalent to “L”. Lambda (l) 1 is the reference voltage of 450 mV. l 1 represents an air fuel ratio of 14.7:1 or stoichiometric. The controller will drive the injector pulse from rich to lean and lean to rich to maintain a stoichiometric air fuel ratio.

http://answers.yahoo.com/question/index?qid=20100103215158AAa4lA8

The Powertrain control module
(PCM) will provide a .45 volt reference voltage to the Oxygen sensor. When the O2 sensor reaches operating temperature, it will generate a voltage that will vary depending on the oxygen content of the exhaust.

http://www.sjmautotechnik.com/trouble_shooting/10vo2sen.html

If the O2 sensor wire is disconnected with the engine running, the ECU normally has a 0.450 V (+/- 0.050V) reference voltage on the ECU wire connecting to the O2 sensor.
 
Unless I am mistake (and I don't think I am), the 90 model was a Renix, not OBD-I. Also Renix used a 5 volt not a 1 volt signal. So they have 2 errors in those links.

I don't get the reference voltage on OBD-I and II, It makes absolutely no sense to me at all why they would have the computer send a reference voltage to a voltage producing sensor while it is running. That just seems bizzare.

Have you actually seen .45 volts on the sensor "computer side" wire of a disconnected O2 sensor on 91-01 model while the engine was running? I understand you said earlier that you have seen it, with power on, engine off... or something to that effect. I don't have any non renix jeeps, and I have not played with son's 96 Ford Taurus O2s yet (but that happen soon) so IO have no way currently to verify it.

Thanks for your posts and contributions (I do appreciate your input!;)), but for others reading this thread, let me say that I started it because of the number of wrong and incomplete posts on other sites that had incomplete information on our O2 sensors or info that was simply wrong. So don't take my arguments the wrong way, I just have seen so much wrong stuff, I don't take anything at face value anymore.
 
The guy answering on the yahoo site:

http://answers.yahoo.com/question/index?qid=20100103215158AAa4lA8

Contradicts himself, he goes from a .45 V reference voltage statement early on to a 5 volt signal from the PCM to the O2 sensor later in his same disertation. Not sure what to make of that. He is answering a question about a 2000 infiniti g2.
 
Unless I am mistake (and I don't think I am), the 90 model was a Renix, not OBD-I. Also Renix used a 5 volt not a 1 volt signal. So they have 2 errors in those links.

I don't get the reference voltage on OBD-I and II, It makes absolutely no sense to me at all why they would have the computer send a reference voltage to a voltage producing sensor while it is running. That just seems bizzare.

Have you actually seen .45 volts on the sensor "computer side" wire of a disconnected O2 sensor on 91-01 model while the engine was running? I understand you said earlier that you have seen it, with power on, engine off... or something to that effect. I don't have any non renix jeeps, and I have not played with son's 96 Ford Taurus O2s yet (but that happen soon) so IO have no way currently to verify it.

Thanks for your posts and contributions (I do appreciate your input!;)), but for others reading this thread, let me say that I started it because of the number of wrong and incomplete posts on other sites that had incomplete information on our O2 sensors or info that was simply wrong. So don't take my arguments the wrong way, I just have seen so much wrong stuff, I don't take anything at face value anymore.

The .450 volts is a reference voltage for the ECM's O2 input transistor. The presence of a steady-state .45 tells the ECM, by electronically comparing the input voltage to the reference, that the O2 sensor is inactive. When the sensor starts generating the varying DC volts, the ECM is able to determine when the O2's output is <,= to, or > than the .45v reference.
And yes, I have personally measured this reference voltage numerous times, in my Chevy ECM, which uses a common zirconia O2 sensor. The references I quoted are of different vehicles, all with the zirconia sensor. It appears, based on my unscientific sample, that the common scheme for monitoring a zirconia sensor, by the ECM is the use of a .450v reference signal generated internally by the ECM. I know that to be true with the GM ECM/PCMs. I believe it's true of other applications using the zirconia sensor; however, if you need certainty, I suggest you research it further.
My '88 Cherokee now has a '94 Chevy engine installed, so I'm not motivated to spend the effort validating my reasoning with regard to Renix, or non-Renix Jeep O2 sensors. If I had an OB-I or II Jeep in the driveway, I would have tested it by now---would take about 10 minutes to do.
I think Ford uses a different style of O2 sensor than we've been discussing. So you may want to research that before testing.
Good luck
 
Unless I am mistake (and I don't think I am), the 90 model was a Renix, not OBD-I. Also Renix used a 5 volt not a 1 volt signal. So they have 2 errors in those links.

90 is Renix.

The general concept of the article is correct but the jeep setup is a little different. The O2 sensor is in series with a fixed resistor and +5VDC is applied to both, then the ECU reads the voltage dropped across the O2 sensor.

Code:
[FONT=Courier New]+5VDC ---/\/\/\/\/\---+---\/\/\/\/\/----- GND
          Fixed R     |       O2
                      |
                     ECU[/FONT]
At full lean, the O2 acts like an open circuit and drops the whole +5V. At full rich the O2 sensor acts like a short and drops zero volts. At stoichiometric, it's R is equal to the fixed R, and it drops 2.5VDC.

This schematic is in the RENIX FI Manual, BTW.
 
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Hypothesis: A Renix O2 sensor can be tested with a digital volt meter.

Test 1: Using an analog meter
http://www.youtube.com/watch?v=VRzXMWjTrck

Observations: It's nice and smooth. You can easily see how it dwells momentarily at the far ends of it's range.

Test 2: Using a digital meter
http://www.youtube.com/watch?v=B6YPzAWV8mQ

Observations: It is jumpy. But on every cycle you can see it hit the top and bottom of it's range and usually see at least one sample in the middle.

Conclusion: The analog meter is better, but the digital meter is adequate.

Any further remarks on this topic are !!!1 .
 
Hasta


LOL.
 
One more thing, if any one of the grounds or the O2 sensor to ECU/PCM wire reads a high voltage chances are the wiring harness is damaged and the 12-14 volts for the O2 sensor heater is getting through a bad spot in the wires insulation and contacting a ground wire or the O2 sensor wire feed to the ECU/PCM. Also not the O2 sensors fault, but a wiring problem.
My xj has a code for O2 high voltage and the harness is infact damaged, casing got warn away from falling on drive shaft. I also have a code saying it is running lean causing me to run rich and having poor MPG. both mention bank. 1 could this be linked to the Harness being damaged? f not any ideas on why it says I'm lean??
 
My xj has a code for O2 high voltage and the harness is infact damaged, casing got warn away from falling on drive shaft. I also have a code saying it is running lean causing me to run rich and having poor MPG. both mention bank. 1 could this be linked to the Harness being damaged? f not any ideas on why it says I'm lean??

Yes, the 12 volt wire is probably shorted to one of the other O2 sensor signal wires, likely the 0-1 volt output wire, causing the lean condition and the high voltage computer alarm. Fix the harness, and that may fix the entire problem, unless the high voltage damaged the sensor or computer, but I suspect they are designed to handle that short. I know renix can handle that short, as I had the same problem, but I had no way to ask the renix computer what the problem was. I had to hunt for it with an ohm meter, the OLD FASHIONED WAY! Good luck.
 
My brother also has had his o2 sensor wires get caught in the driveshaft and ripped to pieces. Out of his rear o2 are the 4 wires but the other side of the plug harness only has two wires-can you point me in the direction of a wiring diagram for him to repair, or are the two ground wires grounded somewhere in between the pigtail of the o2 and the connector for the o2? He has a 97
 
Update. I discovered that the feed voltage to the O2 sensor heater on my 89 is only 5 volts, not 12 volts like my 87.
 
Thanks for the thread, Got me thinking about my very poor 10mpg with 4.56 gears.

The relay for the heater was bad, I was poking around with a power probe and everything else is good.

The engine idles a lot smoother, no hesitation off the line and you can smell the exhaust is not rich smelling if you know what I mean.
 
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