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Discussion Starter · #1 ·
I have been getting pretty poor gas mileage lately (12-15 mpg) so I was all set to replace my O2 sensor today as that seems to be the cause of a lot of everyone else's problems. Before I got into the engine, I decided to rum my ECU codes and I followed the instructions in the Hayne's manual. Before I replaced the sensor, the computer would flash green, stay lit, flash red, and then both lights would go out. This would repeat over and over. As this varied from the description in the manual, I set to replace the sensor. Now that the sensor is new, the computer is still flashing the same lights. What's up?
 

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I might be wrong but I think after you replace anything the computer says is bad you need to reset the computer by taking off the battery cable for a minute and putting it back on .
If i am wrong I'm sure someone will let you know.
 

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Discussion Starter · #3 ·
OK, so I disconnected the battery and checked the code again. Instead of the one light flashing and then the other, now both flash simultaneously. I know a lot of you have changed your O2 sensors, has anyone ever checked to see if their code was erased? Thanks guys.
 

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I'll add that the manual should also describe the procedure to erase stored error codes.
Also, the exact procedure to monitor O2 function is different on the late cars. Is it a 87+?



Post Edited (Aug 21, 9:51pm)
 

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Discussion Starter · #6 ·
The car is an '84 turbo. Today I took your advice and actually erased the codes as the manual describes, and ran the check again. After the car has been running at 2 grand and the "screw" on the ECU is turned counterclockwise, the ECU flashes both red and green evenly when the car is run at 2000 rpm's. According to the manual, wouldn't that mean that the problem is still present?
 

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Discussion Starter · #8 ·
So I'm cool then? How come it's flashing different than before?



Post Edited (Aug 22, 2:51pm)
 

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Don't know.
It wouldn't hurt to check the ECU part number against the parts fiche to make sure the ECU suits that car.

Going by the PDF 84 FSM, both LEDs should flash at idle when the TPS connector is disconnected, but that FSM does not specify a flash rate under that condition (like it does for the 2000rpm no-load test).

I think some people put too much faith in the O2 sensor. If the basic tune of the engine is correct then the O2 sensor only fine tunes the mixture under closed-loop coditions, and even then the FSM does not go into details as to what triggers closed-loop operation.
 
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