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Disconnected O2 Sensor, Car Runs Better?????

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Old 06-07-2001, 10:49 PM   #1
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Join Date: Sep 2000
Location: Bowmanville,Ontario Canada
Posts: 1,075
Car: 1990 Iroc Z Convertible
Engine: LB9
Transmission: 700R4

Disconnected O2 Sensor, Car Runs Better?????

Been having problems with my car as of late,after it warms up it runs rough, nearly cutting out but catching itself just in time. Did the paper clip analysis and came up with a code 45(Car running Rich).Diconnected the O2 sensor because it was the easiest thing to try. Car now runs better, It has been disconnested for 3 days, car runs smooth most of the time, a little rough periodically. Check engine light comes on after a while, but is not on after start up(takes a while). A Mechanic friend brought home a analyser which also gave us a code 45, funny thing is that after he took the power supply out of the lighter socket the engine idle increased. He thinks my computer is faulty.Shouldn't the car run like a complete Piece of crap if the O2 sensor is disconnected? Do you guys think my computer is Fubared?????

1990 Iroc convertible,305 tpi,Black with black leather interior,lowered,Taylor 8mm wires,K&N's
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Old 06-08-2001, 12:34 AM   #2
Join Date: Jun 2001
Location: Oklahoma City, OK. USA
Posts: 215

Have you thought about replacing the O2 sensor?

If the O2 sensor is bad it is very possible that with the carbon/crap on the sensor that it is telling the ECM that your engine is running very lean hence will give the engine unwanted fuel causing that rough running problem you are having.

Because the oxygen sensor does not perform properly at low temperatures, two modes of operation are employed. The modes are referred to as "closed-loop" and "open-loop." Open-loop mode is utilized during engine warm-up. During open-loop the fuel delivery system does not recognize or use the information from the oxygen sensor until a temperature of approximately 600 deg. F is obtained. Once the operating temperature is achieved, the system enters closed-loop mode were the oxygen sensor information is routed to the ECM to control the fuel and air delivery. Your O2 sensor maintains a 14.7 to 1 air fuel mixture for gas mileage and emittions.

If you leave the O2 sensor disconnected expect a 7 MPG decrease in fuel economy or worse.

An O2 sensor is $30.
A gallon of gas is $2.

[This message has been edited by whiteroc (edited June 07, 2001).]
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Old 06-08-2001, 12:35 AM   #3
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Location: Hayward, CA
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Car: 91 camaro
Engine: 383
Transmission: T56

Have you tried replacing the O2 sensor yet? They're a lot cheaper than a computer; they cost about $25. You're car runs good when it is cold because when it is cold the computer ignores the O2 sensor. This is also why it takes a few minutes to throw a code when the sensor is unplugged. Until a certain temp, the computer is ignoring the O2 sensor and therefore doesn't know it's unplugged. When it warms up, then it takes info from the sensor.
Try this: plug the sensor back in, and start the car. Then take a paperclip, and jump A and B like you would to get a code. The SES light will flash fast, like two times per second. This means the car is in open loop, or not taking info from the O2. When it goes into closed loop and starts reading the O2, the light will fluctuate between on and off every few seconds (at least it would if everything was functioning properly, yours may stay on since code 45 is for rich) On means rich, off means lean. But what you should look for is if your idle goes to crap at the moment the car goes into closed loop. I suspect that it probably will. This is just to confirm that your problem is related to the O2 sensor. Of course the problem could be the sensor, the computer, or something else. Hope this wasn't too confusing.

91 Z28
Come see The Vicious...

Hmmm... looks like someone beat me to it.

[This message has been edited by ViciousZ (edited June 07, 2001).]
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Old 06-08-2001, 09:00 AM   #4
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Join Date: Jan 2001
Location: PA
Posts: 1,978
Car: 88 Firebird WS6
Engine: 350 TPI
Transmission: T56
Axle/Gears: 3.42

A lazy at idle alternator may cause this also. Whats your idle voltage.

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Old 06-12-2001, 01:06 AM   #5
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Join Date: Sep 2000
Location: Bowmanville,Ontario Canada
Posts: 1,075
Car: 1990 Iroc Z Convertible
Engine: LB9
Transmission: 700R4

I did buy a new O2 sensor, however the one in the car now looks new. I will replace it this weekend and see if it makes a difference. The above info makes sense and I hope the O2 sensor is the problem since there can be alot of other things wrong with a code 45.
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