BEYOND DESPARATE! No O2 signal after starting! Does work before starting!
06-23-2010, 10:38 AM
#1
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BEYOND DESPARATE! No O2 signal after starting! Does work before starting! I could write a novel on how these o2 sensors have driven me crazy. I have a 408 ls1 stroker in a 1950 Chevy truck and have deleted all emission items and rear o2 sensors. I have had a local professional tuner come to my house for the third time to baseline tune my truck so I can break-in the new motor and trans before it goes to be dyno'd. The truck runs and all sensors have signal input to the PCM. The o2 sensors flatline at 450 mV. So I swapped the sensors, same result. Then I completely removed the 02 sensor wiring and put in a new o2 sensor harness with its own dedicated ground and ignition power. This morning we plugged a TECH II scanner into the truck and turned the ignition on. We got a signal: 300mv, 700mv, moving around, and so on. He wrote a new OS (Efi-Live System #3 ?) and started it. The same result, no o2 signal, flatline at 450 mV. I am desparate here, this has kept me from about 3 months of car shows and I just want to drive my truck. Any help would be appreciated. Questions are welcome if I need to be more specific. Thanks!
06-23-2010, 11:22 AM
#2
Perform on cool engine.
Connect scan tool.
Turn on ignition, engine off.
Monitor O2 voltage.
O2 Voltage should change from bias voltage of 450 MV to either above or below 300-700 MV.
If the sensor is at the operating temperature the HO2S voltage will stay high or low. If the HO2S voltage stays between 300-700 mV indicates the HO2S heater is inoperative.
Connect scan tool.
Turn on ignition, engine off.
Monitor O2 voltage.
O2 Voltage should change from bias voltage of 450 MV to either above or below 300-700 MV.
If the sensor is at the operating temperature the HO2S voltage will stay high or low. If the HO2S voltage stays between 300-700 mV indicates the HO2S heater is inoperative.
06-23-2010, 12:01 PM
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When the engine was cool, I did not have a scan tool available to me te other day, but I put a multimeter on the purple signal wire and it went above 700 mV when I turned the ignition on. Then this morning we turned the ignition on (cold engine) with a TECH II plugged in and it confirmed that it had a signal. Once we got the engine running, EFI Live showed 450 mV and the TECH II confirmed that.
06-23-2010, 02:21 PM
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After reading these responses I am now officially frustrated with my truck. I want the OEM front o2 sensors to remain and will be tuned for closed loop speed density. It just seems that there is some kind of simple answer to why the o2 sensors stop putting out a signal. They have ignition hot power, both grounds go to the back of the cylinder head, and the ppl and tan wires go to the correct pins on the PCM. Thanks for everyone's responses, but please do not suggest OLSD any more. If anyone needs any further info or engine specs please respond so maybe someone out there can help me figure this out.
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06-23-2010, 03:24 PM
#8
I could write a novel on how these o2 sensors have driven me crazy. I have a 408 ls1 stroker in a 1950 Chevy truck and have deleted all emission items and rear o2 sensors. I have had a local professional tuner come to my house for the third time to baseline tune my truck so I can break-in the new motor and trans before it goes to be dyno'd. The truck runs and all sensors have signal input to the PCM. The o2 sensors flatline at 450 mV. So I swapped the sensors, same result. Then I completely removed the 02 sensor wiring and put in a new o2 sensor harness with its own dedicated ground and ignition power. This morning we plugged a TECH II scanner into the truck and turned the ignition on. We got a signal: 300mv, 700mv, moving around, and so on. He wrote a new OS (Efi-Live System #3 ?) and started it. The same result, no o2 signal, flatline at 450 mV. I am desparate here, this has kept me from about 3 months of car shows and I just want to drive my truck. Any help would be appreciated. Questions are welcome if I need to be more specific. Thanks!
When the engine was cool, I did not have a scan tool available to me te other day, but I put a multimeter on the purple signal wire and it went above 700 mV when I turned the ignition on. Then this morning we turned the ignition on (cold engine) with a TECH II plugged in and it confirmed that it had a signal. Once we got the engine running, EFI Live showed 450 mV and the TECH II confirmed that.
06-23-2010, 03:52 PM
#9
You don't need All Data or a scan tool to check the heaters.
O2 removed, key on engine off, does it get hot?
No, recheck power and grounds to O2 sensor since they are new.
Yes, check the wiring to the PCM for the high and low signals, you said you ran new power and ground but you did not mention the PCM signal wires.
O2 removed, key on engine off, does it get hot?
No, recheck power and grounds to O2 sensor since they are new.
Yes, check the wiring to the PCM for the high and low signals, you said you ran new power and ground but you did not mention the PCM signal wires.
06-23-2010, 05:38 PM
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2xLS1, I sincerely apologize if it appeared that I changed my story. I tested the o2's on two different occasions on two different days, once with a multimeter and once today with a TECH II. Those were the readings that were observed. ItI just did the "manual" o2 heater test by removing them from the pipes and feeling them with the key on. In about 30 seconds, they were very hot. Both sensors responded the same way. To answer the question about the o2 to PCM wiring, I replaced both purple and tan wires all the way to the PCM and crimped new pins on the end. The o2 wiring is completely new. Keep the comments rolling in, believe me, I really appreciate every single comment.
06-23-2010, 10:00 PM
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I guess that no one has ever encountered this problem before. When I fix it, and I know I eventually will, I will post the solution to help others in the future.
06-25-2010, 09:03 AM
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450mV steady, means the PCM has jammed the outputs
to that level. It does that for certain sensor faults (real
or imagined). What kind of codes do you see? Maybe you
have set them up for no light, but still bugging. Change
any heater or switching codes you find, to "Enabled, No
Error Reported" (option 3 in HPTuners, dunno how EFILive
expresses it).
to that level. It does that for certain sensor faults (real
or imagined). What kind of codes do you see? Maybe you
have set them up for no light, but still bugging. Change
any heater or switching codes you find, to "Enabled, No
Error Reported" (option 3 in HPTuners, dunno how EFILive
expresses it).
08-15-2010, 07:59 AM
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Update, I trailered my truck to the dyno the other day for some tuning and they put their best guy on troubleshooting the 02 sensor problem. He printed off his own diagrams and checked all the wiring in the 02 harness and all PCM grounds. They all were fine. He then checked the 02's against another known good 02. They were ok. Then the shop looked at the 02 sensor output on the dyno and it stayed at 450 mv. They plugged in another PCM and it read 450 mv also. They said they have only seen this happen on only one other vehicle and that problem still isn't solved either. Could it be an electrical fault in another circuit of the harness that is feeding back through the PCM and interrupting the 02 signal?
05-15-2013, 07:36 PM
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Update, I trailered my truck to the dyno the other day for some tuning and they put their best guy on troubleshooting the 02 sensor problem. He printed off his own diagrams and checked all the wiring in the 02 harness and all PCM grounds. They all were fine. He then checked the 02's against another known good 02. They were ok. Then the shop looked at the 02 sensor output on the dyno and it stayed at 450 mv. They plugged in another PCM and it read 450 mv also. They said they have only seen this happen on only one other vehicle and that problem still isn't solved either. Could it be an electrical fault in another circuit of the harness that is feeding back through the PCM and interrupting the 02 signal?
05-16-2013, 05:59 AM
#18
TECH Addict
Are the 02's for your system suppose to be case grounded? I would also check all your grounds and or add some from motor to frame. What kind of wiring harness do you have?
