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  #31  
Old February 4th, 2010, 21:33
xjbubba xjbubba is offline
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by Ecomike View Post
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
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  #32  
Old May 5th, 2010, 12:28
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by Ecomike View Post
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:
+5VDC ---/\/\/\/\/\---+---\/\/\/\/\/----- GND
          Fixed R     |       O2
                      |
                     ECU
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.

Last edited by n1ywb; May 5th, 2010 at 12:38.
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  #33  
Old May 5th, 2010, 12:40
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Re: Testing Jeep O2, Oxygen sensors

This wikipedia article describes our Renix O2 sensor to a T: http://en.wikipedia.org/wiki/Oxygen_...Titania_sensor
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  #34  
Old May 6th, 2010, 18:55
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Re: Testing Jeep O2, Oxygen sensors

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 .
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  #35  
Old May 6th, 2010, 19:03
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Re: Testing Jeep O2, Oxygen sensors




LOL.
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  #36  
Old May 27th, 2010, 13:21
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by Ecomike View Post
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??
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  #37  
Old May 27th, 2010, 21:54
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Re: Testing Jeep O2, Oxygen sensors

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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.
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  #38  
Old June 26th, 2010, 11:47
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Re: Testing Jeep O2, Oxygen sensors

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
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  #39  
Old January 20th, 2011, 18:50
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Re: Testing Jeep O2, Oxygen sensors

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.
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  #40  
Old January 24th, 2011, 13:00
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Re: Testing Jeep O2, Oxygen sensors

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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  #41  
Old January 24th, 2011, 13:07
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by Ecomike View Post
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.
that is odd, I thought the heaters were always 12 volts and the sensor side was always 5. Running the heater off 5 volts seems wrong, because that large a current draw will cause a voltage drop across the harness and skew the computer's idea of the rest of the sensor readings.
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  #42  
Old January 24th, 2011, 13:15
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by kastein View Post
that is odd, I thought the heaters were always 12 volts and the sensor side was always 5. Running the heater off 5 volts seems wrong, because that large a current draw will cause a voltage drop across the harness and skew the computer's idea of the rest of the sensor readings.
If It had not been dead on 5 V, if it had been 6 or 7 volts, I would have looked at the relay connectors, etc. Still seems to odd to me, but until some one elses posts an 89 to confirm a 12 V or 5 V reading on the heater, data is data, and the sensor was working and the MPG is 20 to 24 mpg on this 89 XJ (stock 2WD), when the POS starts, LOL!

Begs the question as to the 5 volt source, and relay wiring?

I will retest it when I get a chance. Maybe I was reading the wrong scale or something, but I never make mistakes (LOL)
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  #43  
Old January 27th, 2011, 07:27
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Re: Testing Jeep O2, Oxygen sensors

I scanned through the entire thread and did not see this posted anywhere, sorry if its been covered...

Where is the best place to physically attach the multimeter to test these voltages/resistances? It sounds like I'll have to strip some wires or something.
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  #44  
Old January 27th, 2011, 09:45
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Re: Testing Jeep O2, Oxygen sensors

Most people back probe the quick connect, from the wire side of the QC. I sometimes solder and splice an extra QC and wires in parallel for test purposes, if I end up doing frequent testing in the same place. Some just use the probe tip and non conductive backing behind the wire to pierce the insulation in a tiny spot to get the signal.
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  #45  
Old January 27th, 2011, 11:24
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by Ecomike View Post
Some just use the probe tip and non conductive backing behind the wire to pierce the insulation in a tiny spot to get the signal.
I have done this when very frustrated but I strongly suggest not doing it. Any kind of opening in the insulation will allow water in, if you think the XJ has problems with a stock wiring harness you should see one that has a badly internally corroded wiring harness. It's damn near impossible to track down.
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