LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Car won't stay in closed loop. Whats causing it?

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Old Mar 16, 2008 | 10:38 AM
  #1  
mrmint69's Avatar
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Car won't stay in closed loop. Whats causing it?

I was looking at someones datalog and the car would go from closed loop to open and back several times during the run. There were several DTC codes set so what would cause it to change back and fourth?
Old Mar 16, 2008 | 11:07 AM
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IMHO, address the DTCs first. If they are for O2s, for instance, it might cause your loop issues.
Old Mar 16, 2008 | 11:28 AM
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The O2's both show they have failed. They will read 400's for several times in a row and then go to the 500's and repeat. One side won't reach the 900's during wot so replacement will be necessary.
Old Mar 16, 2008 | 12:05 PM
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The PCM can't control the A/F ratio in closed loop without the O2 sensors. If you have an active code for a sensor, its only logical it would revert to open loop.
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