C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Stuck in Open Loop

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Old Jan 23, 2010 | 06:09 PM
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Default Stuck in Open Loop

My '87 runs pretty good except it seems to stay in open loop

I set the minimum air, set tps to .56 and checked it out on the scanner

coolant temp is about 185f / 85c but the oxygen sensor voltage wont budge from .36 volts

do i need a new oxygen sensor or is there some other issue somewhere?
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Old Jan 23, 2010 | 07:18 PM
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When you rev the engine, the o2 voltage should change, it makes it's own voltage from heat & oxygen in the exhaust. It should range from 0.90s to 0.10s on the scanner.
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Old Jan 23, 2010 | 08:17 PM
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Originally Posted by DrEvil11417
the oxygen sensor voltage wont budge from .36 volts
do i need a new oxygen sensor or is there some other issue somewhere?
Would be a good start, when did you change it last?
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Old Jan 24, 2010 | 03:41 AM
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Originally Posted by rodj
Would be a good start, when did you change it last?
I've had the car for a few months and I have no idea how old the oxygen sensor is

If I rev the car it doesn't change at all, it just hangs out around .33-.35v
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Old Jan 24, 2010 | 06:58 AM
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I'd say bad 02, once over 140* water temp it should be fluctuating up and down over the crossover point. Is it a heated sensor, or stock loctaion ?
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Old Jan 24, 2010 | 10:44 AM
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Originally Posted by mseven
I'd say bad 02, once over 140* water temp it should be fluctuating up and down over the crossover point. Is it a heated sensor, or stock loctaion ?
no it's not a heated sensor, and it's got long tube headers
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Old Jan 24, 2010 | 10:55 AM
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where is the bung for the sensor located?? If you have long tubes and the sensor is near the collector, you need a heated sensor...
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Old Jan 24, 2010 | 11:20 AM
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If it stays in open loop, the engine cooling temp sensor that feeds the computer is what makes the ecm fall back into closed loop, not the oxygen sensor.
the difference between closed loop and open loop is temperature.............
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Old Jan 24, 2010 | 11:23 AM
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How ever a good O2 sensor will still show fluctuations during open loop.

Two problems

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Old Jan 24, 2010 | 12:56 PM
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Originally Posted by coupeguy2001
If it stays in open loop, the engine cooling temp sensor that feeds the computer is what makes the ecm fall back into closed loop, not the oxygen sensor.
the difference between closed loop and open loop is temperature.............
the scanner shows 85 degrees while the dash says 185 degrees, im assuming the scanner is reading it in celsius because 85 celsius is 185 fahrenheit

but ill go back and read the book just in case!

i was always under the impression the heated o2 sensor was mostly for idle since under load the exhaust gets more than hot enough to get the oxy sensor going
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Old Jan 24, 2010 | 10:37 PM
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the tip of the sensor needs to get up to 600 degrees to work properly...the only place a non heated sensor would see that temp is right at the exhaust port...thats why stock manifolds have the bung there...
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Old Jan 25, 2010 | 06:50 AM
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DrEvil there are 2 coolant temp sensers, 1 for gauge, the other for the ecm. Does the upper rad hose get to hot to touch?
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