O2 sensor good or bad?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: O2 sensor good or bad? (sinistervette)
I had a bad O2 sensor in my IROC that didn't set a code.
Jumper ALDL pins A&B, start the engine and watch the flashes of the SES light. After a minute of two the flashes should settle to about 1Hz. Then raise the idle to 2,000-2,500rpm and hold till for 30 sec.
In each case the SES flashes should be of equal On & Off duration. This indicates the ECM is in closed loop mode and the O2 sensor is fine.
Jumper ALDL pins A&B, start the engine and watch the flashes of the SES light. After a minute of two the flashes should settle to about 1Hz. Then raise the idle to 2,000-2,500rpm and hold till for 30 sec.
In each case the SES flashes should be of equal On & Off duration. This indicates the ECM is in closed loop mode and the O2 sensor is fine.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: O2 sensor good or bad? (sinistervette)
When the engine is first stared and WOT operation it is in open loop mode. Here the ECM looks at all sensors EXCEPT the O2 sensor to determine air/fuel mix.
After the engine warms up, a fixed amount of time has elapsed, and the O2 sensor is OK the ECM enters closed loop mode and stays there during part throttle operation. During closed loop mode the ECM uses data from the O2 sensor to assure stoch air/fuel mix.
This is the main reason our EFI cars get such terrific gas mileage and still have great performance potential.
After the engine warms up, a fixed amount of time has elapsed, and the O2 sensor is OK the ECM enters closed loop mode and stays there during part throttle operation. During closed loop mode the ECM uses data from the O2 sensor to assure stoch air/fuel mix.
This is the main reason our EFI cars get such terrific gas mileage and still have great performance potential.
Racer
Joined: Sep 2002
Posts: 270
Likes: 1
From: Torrance California
Re: O2 sensor good or bad? (sinistervette)
I read on another forum you should change them about every 50k. Even if there is no trouble code. Reason being is that it takes a certain voltage to set the code, and just because there is no code does not mean your 02 is good. Main thing to look for is rough idling, and poor mileage. Personally on my 97 Suburban I will wait for the code. Cost per 02...$125.00 x 4....... :eek:
Melting Slicks
Joined: Nov 2000
Posts: 3,388
Likes: 1
From: X
Re: O2 sensor good or bad? (sinistervette)
You can test an 02 with a volt meter and a torch...But an oscilloscope is idel.
http://www.wellsmfgcorp.com/counterp...erpoint2_3.pdf
http://www.wellsmfgcorp.com/counterp...erpoint2_3.pdf
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Racer
Joined: Jun 2002
Posts: 296
Likes: 0
From: Auburn ca
Re: O2 sensor good or bad? (JonM)
Sometimes they just need to be cleaned. To do this unpluge a vacume line, a good one unplug would be the brake booster. Then reve the motor to 2000rpm for one minute and then plug the vacume line back on. It worked for me. Got this tip from an old machanic.
Burning Brakes
Joined: Apr 2002
Posts: 755
Likes: 0
From: Patterson CA
Re: O2 sensor good or bad? (sinistervette)
Ecklers sells a test tool for about $15.
I'm not sure about yours, but on my '89 the O2 sensor is only $25 so I replace it every 6 months with the fuel filter and plugs.
Just my .02 :rolleyes:
I'm not sure about yours, but on my '89 the O2 sensor is only $25 so I replace it every 6 months with the fuel filter and plugs.
Just my .02 :rolleyes:
Racer
Joined: Jul 2002
Posts: 412
Likes: 0
From: corvallis or
Re: O2 sensor good or bad? (sinistervette)
O2s can be moving back and forth from rich to lean but not be in the proper voltage range. The flashing light method will let you know its switching but will not let you know what ranges. General replacement is 30k for the single wire and 60-90k for the 3 and 4 wire heated sensors. Those milege guidlines are designed because your signal may be switching and not setting codes but may not be working through the full voltage range it is designed for.
