Unplug injector and read change in O2 sensor volts: any diagnostic value?
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vancouverbc
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- Car: 1991 240sx
Unplug injector and read change in O2 sensor volts: any diagnostic value?
When i disconnected(electrical plug) fuel injector 1 and 2 , I created a rich condition of around .55 volts. When I disconnected 3 and 4, i got a lean condition of around .130 volts. With all injectors firing, the reading is around .9 volts. I'm only rich at idle.
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Re: Unplug injector and read change in O2 sensor volts: ... (vancouverbc)
The ecu suppies a bias voltage to O2 of around 0.45-0.55 volts to enforce the midpoint [14.7AF}.
The ecu just looks at leaner [<0.45]and richer [>0.55] than 14.7 and changes the injector time by a tiny increment [say 0.1 millisec] and looks at O2 result.The ecu has a trim range of +- 20% in millisecs from the calculated value so if the first 0.1 or 0.01 doesn't do it it keeps going in same direction at the next rpm and so on and so forth until 14.7 or it hit the 20% wall.
At idle the O2 is ignored because there is not enough exhaust flow or heat to create accurate readings.
Remember the first ~ 1 millisec is the time to open the injector so no fuel flows during that time and real flow time is the next millisec or fraction there of.
The test of an O2 sensor is how many times or how fast it switches lean to rich in a short period as they age they get slow and sluggish which reduces mpg as they stay rich too long
The ecu just looks at leaner [<0.45]and richer [>0.55] than 14.7 and changes the injector time by a tiny increment [say 0.1 millisec] and looks at O2 result.The ecu has a trim range of +- 20% in millisecs from the calculated value so if the first 0.1 or 0.01 doesn't do it it keeps going in same direction at the next rpm and so on and so forth until 14.7 or it hit the 20% wall.
At idle the O2 is ignored because there is not enough exhaust flow or heat to create accurate readings.
Remember the first ~ 1 millisec is the time to open the injector so no fuel flows during that time and real flow time is the next millisec or fraction there of.
The test of an O2 sensor is how many times or how fast it switches lean to rich in a short period as they age they get slow and sluggish which reduces mpg as they stay rich too long
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vancouverbc
- Posts: 3197
- Joined: Thu Oct 30, 2003 1:30 am
- Car: 1991 240sx
Re: Unplug injector and read change in O2 sensor volts: ... (Q45tech)
Interesting. I have the O2 sensor disconnected from the computer. I can get a reading of .130 if I discconect the two worst injectors. These are the two injectors at the front which are furthest from the O2 sensor and fuel regulator. With only two injectors firing , it is obviosly a lot easier to read lean as two cylinders have only air and the O2 sensor reads lean at low temperature. Disconnecting the two injectors closest to fuel regulator, yields a reading of .55 volts. I guess if I had a base I might be able to make some sense of these numbers.