Problem with O2 sensor
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Senior User
Joined: Jan 2003
Posts: 383
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From: Newport News USA
Problem with O2 sensor
it actually shows the major grounds? I've looked through the manual many times now to include going over the wire diagrams for my year and I don't see it. Am I missing it? Are they actually part of the diagrams in the back of the manual or somewhere else? Do you know which exact block of the diagram it's in, cuz the manual doesn't list general grounds.
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Senior User
Joined: Jan 2003
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From: Newport News USA
Problem with O2 sensor
If the O2 sensor doesn't "switch" at idle, but does react to the throttle when applied, is it a problem with the O2 sensor or something else? Seems that the computer isn't seeing a switching from the O2 sensor so it resorts to the default a/f mixture and then doesn't adjust throughout driving conditions. What might cause this? Is the computer not actually adjusting the injectors to make the switching happen.
If I'm completely off base, somebody please let me know. I've monitored the O2 sensor sig line from startup to about 5-8 minutes. From the get go, the voltage jumps above 1volt (when cold, upwards of 3.8v), and then continuously drops until the computer reverts to the default(5-8 minute mark). At that point it jumps up to 1.2-1.5 volts and holds steady.
I've checked all grounds, rewired some, and even added a few to make sure.
Has anyone ever run into this prob where the O2 sensor didn't "switch", and if so what were the symptons and/or solutions.
Apologize for the long posts.
All help makes you my best friend!!
Thanks in advance.
Luke
If I'm completely off base, somebody please let me know. I've monitored the O2 sensor sig line from startup to about 5-8 minutes. From the get go, the voltage jumps above 1volt (when cold, upwards of 3.8v), and then continuously drops until the computer reverts to the default(5-8 minute mark). At that point it jumps up to 1.2-1.5 volts and holds steady.
I've checked all grounds, rewired some, and even added a few to make sure.
Has anyone ever run into this prob where the O2 sensor didn't "switch", and if so what were the symptons and/or solutions.
Apologize for the long posts.
All help makes you my best friend!!
Thanks in advance.
Luke
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Joined: Jan 2001
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From: Rural Florida Panhandle
Problem with O2 sensor
Well, I just re-read your first post.
First - there is no way the o2 sensor can generate voltage that high. There has to be a bleed or short to some other source.
You checked the heater voltage to the sensor. Is it possible that the sensor itself has an internal short? Do you still have the old one that you could substitute in to check?
Can you disconnect the harness from the computer and the sensor and check the signal line for a high resistance to any other wire in the harness, or to ground?
I just can't give up on this one. There just has to be a voltage bleed from somewhere, and you have already replaced the computer.
I have 5 or 6 old sensors, and have tested them using the propane torch method, and all run between .5 and .7 volts max.
???
First - there is no way the o2 sensor can generate voltage that high. There has to be a bleed or short to some other source.
You checked the heater voltage to the sensor. Is it possible that the sensor itself has an internal short? Do you still have the old one that you could substitute in to check?
Can you disconnect the harness from the computer and the sensor and check the signal line for a high resistance to any other wire in the harness, or to ground?
I just can't give up on this one. There just has to be a voltage bleed from somewhere, and you have already replaced the computer.
I have 5 or 6 old sensors, and have tested them using the propane torch method, and all run between .5 and .7 volts max.
???
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Senior User
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From: Newport News USA
Problem with O2 sensor
I have pulled the O2 sensor, and tested it using a torch (easily getting 1.0 volts), as well as swapping it out with another O2 sensor that also tested fine. Did the resistance testing of all three wires on the sensor, no prob there either. Have even gone as far as to replace the entire sig return line, as well as a lil rewiring of the harness itself. All grounds seem to be good. I was talking to one of the techs who works at the local dealership and he said he "thought" there was supposed to be a reference voltage from the computer, but I've never heard of that or read it anywhere. Is he right or was he just "thinking" too hard? after that... I'm running in circles.
Thanks again Winford!!!
Thanks again Winford!!!
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From: Rural Florida Panhandle
Problem with O2 sensor
< O2 sensor is installed in the cat .> Do you think this could be your problem? Is it really inside the converter? I believe it should be before the converter. I have no experience with other than stock setups.
Is it possible that you have a gasket between the converter and the header that is causing a poor ground for the sensor? I would think that the bolts ground it if that was the case.
Sorry, I 'm all out of guesses for now.
One last gasp for the poor ground theory; with the power on, check for any voltage between the body of the sensor and the truck ground.
Is it possible that you have a gasket between the converter and the header that is causing a poor ground for the sensor? I would think that the bolts ground it if that was the case.
Sorry, I 'm all out of guesses for now.
One last gasp for the poor ground theory; with the power on, check for any voltage between the body of the sensor and the truck ground.
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From: Newport News USA
Problem with O2 sensor
the dual exhaust kit I'm running I got from Summit, and I wasn't running a cat for a while, so to try and get the system running right, I just had a bung installed in the passenger side exhaust(6 inches past the header) and just yesterday I tried plopping the O2 sensor back in there to see if it made a difference, but alas, it didn't. Same exact readings, and still no switching. I'll try the ground test like you were saying between the O2 sensor body and a ground. But I'm not really too hopeful.
What does the computer control to initiate the switching seen from the O2 sensor? Does it tell the injectors to pump more fuel?
I wish you could see what it does... it's definitely thrown me for a loop!!
Thanks again!!
Luke
What does the computer control to initiate the switching seen from the O2 sensor? Does it tell the injectors to pump more fuel?
I wish you could see what it does... it's definitely thrown me for a loop!!
Thanks again!!
Luke
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Joined: Jan 2001
Posts: 1,124
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From: Rural Florida Panhandle
Problem with O2 sensor
I believe that the switching is simply a change from rich to lean or lean to rich, as you suggested, by changing the pulse width to the injectors. It then looks for a change in voltage from the o2 sensor.
I remember you stated earlier that you get the bias voltage even with the engine off but power on. I have never seen any signal from an o2 sensor without the engine running. That is why I am convinced that there is a wiring problem, but you have exhaused all my guesses.
I remember you stated earlier that you get the bias voltage even with the engine off but power on. I have never seen any signal from an o2 sensor without the engine running. That is why I am convinced that there is a wiring problem, but you have exhaused all my guesses.
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Joined: Feb 2000
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From: Connecticut
Problem with O2 sensor
Pull the computer and measure for continuity between pin 49 on the computer end of the harness connector and the case of the sensor. This is the HEGO ground. Should be close to zero ohms. Also measure to battery negative, should be near zero ohms.
Disconnect the HEGO sensor and measure between pin 29 on the computer end of the harness connector and the vehicle harness side of the HEGO connector dark green/purple wire. It is the pin farthest from the connector latch. This is the HEGO signal. You should measure near zero ohms.
Ohm pin 29 to the rest of the pins at the computer end of the harness connector. You should measure a high resistance to all the pins.
The other two wires at the HEGO end of the vehicle harness should measure near 12 volts with the vehicle running. These are the heater wires.
Measure resistance with the battery disconnected and ign. switch off to eliminate false readings.
Any chance that the HEGO connector could be wired wrong? Above tests should rule that out.
Hope this helps.
Mark
Disconnect the HEGO sensor and measure between pin 29 on the computer end of the harness connector and the vehicle harness side of the HEGO connector dark green/purple wire. It is the pin farthest from the connector latch. This is the HEGO signal. You should measure near zero ohms.
Ohm pin 29 to the rest of the pins at the computer end of the harness connector. You should measure a high resistance to all the pins.
The other two wires at the HEGO end of the vehicle harness should measure near 12 volts with the vehicle running. These are the heater wires.
Measure resistance with the battery disconnected and ign. switch off to eliminate false readings.
Any chance that the HEGO connector could be wired wrong? Above tests should rule that out.
Hope this helps.
Mark
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Senior User
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From: Newport News USA
Problem with O2 sensor
You were all right!! And I apologize for immensely for not listening as well as I should have. My HEGO ground wire (orange wire from the comp) was bad. I rewired it and then that stray voltage was nonexistent!! I have yet to take it out for a drive to see what the voltage looks like while under load, but just at idle, it runs at about .2 volts, and then after about 2 minutes the comp readjusts and the voltage jumps up to .98 volts. Would this be indicative of a lean condition and the computer then reverting to the default a/f mixture? And if so, what might I try doing to even out the mix?
Thanks again for all your help guys. You've given me a lil' piece of mind, and sometimes that's worth more than dollar signs!!!!
Luke
Thanks again for all your help guys. You've given me a lil' piece of mind, and sometimes that's worth more than dollar signs!!!!
Luke
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Joined: Feb 2000
Posts: 482
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From: Connecticut
Problem with O2 sensor
Where did you find the connection to be bad?
Why didn't Ford add a 4th wire to the harness connector for such a critical connection? There is an unused location in the connector. They are relying on all the mechanical connections on the exhaust system to provide a signal return path for the O2 sensor. When your measuring millivolts you cannot tolerate too much resistance. To the best of my knowledge most manufacturers do the same thing. Are they that cheap?
Mark
Why didn't Ford add a 4th wire to the harness connector for such a critical connection? There is an unused location in the connector. They are relying on all the mechanical connections on the exhaust system to provide a signal return path for the O2 sensor. When your measuring millivolts you cannot tolerate too much resistance. To the best of my knowledge most manufacturers do the same thing. Are they that cheap?
Mark
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Senior User
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From: Newport News USA
Problem with O2 sensor
I can't physically say where I found the connection to be bad, cuz I just measured the resistance, found it to be bad, and then rewired it to a "true" ground, after finding out it wasn't grounded. It wasn't truly grounded as far as I can tell, and now it is. So I am SOOOOOOO happy now that it switches, albeit a bit slowly....
I'm gonna try running it off the header tomorrow to see the difference between "2 feet" and closer to "4 feet" from the head.i
The O2 sensor in the cat (close to 4 feet) seems to register a bit slow, even with a sensor that is less than 2 days old. Meaning that it actually switches, but does it very slowly. I'm going to install the sensor in the bung in the header to see what change it does.
Guys,
I want to thank ya'll once again.
Luke
I'm gonna try running it off the header tomorrow to see the difference between "2 feet" and closer to "4 feet" from the head.i
The O2 sensor in the cat (close to 4 feet) seems to register a bit slow, even with a sensor that is less than 2 days old. Meaning that it actually switches, but does it very slowly. I'm going to install the sensor in the bung in the header to see what change it does.
Guys,
I want to thank ya'll once again.
Luke
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