02 milivolts all over the place
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Registered User
Joined: Mar 2002
Posts: 3,245
From: Ocala, Florida
02 milivolts all over the place
I just got myself a scanmaster and the 02 milivolts are all over the place. They basically jump around between 20-900 constantly. Is this normal? 
I thought they were supposed to hold somewhat steady...
I thought they were supposed to hold somewhat steady...
Registered User
Joined: Aug 2002
Posts: 4,676
From: Melvindale, MI, US
Re: 02 milivolts all over the place
Originally Posted by speed_demon24
I just got myself a scanmaster and the 02 milivolts are all over the place. They basically jump around between 20-900 constantly. Is this normal? I thought they were supposed to hold somewhat steady...
I thought they were supposed to hold somewhat steady...
Registered User
Joined: Sep 2004
Posts: 1,152
From: Wyoming
Re: 02 milivolts all over the place
I got about the same thing when i hooked up freescan. My left o2 was somewhat constant, but the right one was all over the place, turned out that the header had burned the right o2 wires...i have yet to drag the stupid desktop comp to the back seat of my car and hook it up again but is certainly gets better gas mileage.
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Registered User
Joined: Mar 2002
Posts: 3,245
From: Ocala, Florida
Re: 02 milivolts all over the place
Originally Posted by Dave89IROC
nope, thats correct, they cycle (switch) past 0.45-0.5 V(450-500 mv) its when they stay some where that there is a problem
Thread Starter
Registered User
Joined: Mar 2002
Posts: 3,245
From: Ocala, Florida
Re: 02 milivolts all over the place
Originally Posted by Jameslt1TA
I got about the same thing when i hooked up freescan. My left o2 was somewhat constant, but the right one was all over the place, turned out that the header had burned the right o2 wires...i have yet to drag the stupid desktop comp to the back seat of my car and hook it up again but is certainly gets better gas mileage.
I'm going to have to take a closer look.
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Joined: Aug 2002
Posts: 4,676
From: Melvindale, MI, US
Re: 02 milivolts all over the place
Originally Posted by speed_demon24
They jump around alot more than between there. They go from 20 milivolts to 900 milivolts and jump around between there constantly, they never hold somewhat steady at all. They dont stay within any range at all, basically from the bottom of what they can read to the top of what they can read.
Registered User
Joined: Aug 2001
Posts: 1,983
From: Jacksonville,fla
Re: 02 milivolts all over the place
everybody seems to be right in one way or another. Under normal driving the the o2 millivolts will jump usually between 450-900 millivolts. Now, the only time they'll go steady is when you go wot. Thats when they "should" be about 800-900 millivolts depending on how rich or lean you are. 
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Registered User
Joined: Mar 2002
Posts: 3,245
From: Ocala, Florida
Re: 02 milivolts all over the place
Originally Posted by MEAN LT1
everybody seems to be right in one way or another. Under normal driving the the o2 millivolts will jump usually between 450-900 millivolts. Now, the only time they'll go steady is when you go wot. Thats when they "should" be about 800-900 millivolts depending on how rich or lean you are.
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Joined: Nov 1998
Posts: 71,098
From: Hell was full so they sent me to NJ
Re: 02 milivolts all over the place
And switching rapidly, over a range of 20-900mV on closed loop is TOTALLY NORMAL.
Read the "Air/Fuel Management" section of my online Scanner guide.... its all covered in there:
http://members.aol.com/InjuneerZZ/ScanMast.htm
The specific paragraph that answers your question:
You might want to read the rest of the document to learn more about the ScanMaster.
Read the "Air/Fuel Management" section of my online Scanner guide.... its all covered in there:
http://members.aol.com/InjuneerZZ/ScanMast.htm
The specific paragraph that answers your question:
When you first hook up your ScanMaster, and start your car, you will be convinced either the ScanMaster is broken, or your car is "possessed". Don't worry…… the unit is SUPPOSED to be flashing constantly changing O2 sensor values. The sensor is extremely sensitive at an A/F ratio of 14.7:1. Go very slightly richer than that (14.6:1) and the voltage can soar to 700mV. Go very slightly leaner than 14.7:1 (say 14.8:1) and the sensor output voltage plummets to 200mV. Since the PCM is constantly juggling the fuel up and down to keep it right at 14.7:1, the voltage is going to jump up and down too. So, you will see that, since the PCM updates it's calculations nearly 10 times per second, the O2 sensor voltages are going to be cycling rapidly back and forth between 100 and 800mV, and you might even see values as low as 050 mV, and as high as 950 mV. THIS IS NORMAL.
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