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Re: Poor gas mileage=bad oxygen sensor????? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 10 Feb 2005 13:39:01
In Reply to: Poor gas mileage=bad oxygen sensor?????, Tino, Thu, 10 Feb 2005 13:14:56 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The O2 fuse isn't what you think it is. The sensor only works when warm. For emissions reasons, you want the sensor warm as fast as possible. The fuse is for the heater coil in the sensor. It gets the sensor warm in about 2 minutes. Without the heater, it takes a minute or two more before the exhaust temp gets it warm enough.
It's very hard to test the O2 sensor. If it's dead failed, that's one thing. But as they age, they don't respond as fast, and that's hard to test.
When you pulled the plugs, how did the old ones look? Black from rich running?
In '87, there is a mixture adjustment on the Air Mass Meter. I would try that first. Check out Ander's post:
http://www.saabnet.com/tsn/bb/900/index.html?bID=210522
The test connector signal is an amplified and squared-up version of the O2 sensor signal. THe O2 sensor (while still connected to the ECU) swings between 0.2 and 0.9 volts (lean to rich, respectively). If it's stuck at 0.9, that means rich. The sensor only works in a very narrow band, so slightly rich is 0.9, rich is 0.9, and incredibly rich is 0.9.
When the AMM is adjusted right, the O2 sensor signal swings back and forth from 0.2 to 0.9. That mixture swing is required to make the catalytic converter work right. That corresponds to a signal on the test connector bouncing between 0 and 12 volts. It goes back and forth about 1/second. Ideally, you want to adjust the signal to get the signal to spend 50% of the time at 12 volts, 50% at 0 (at test connector); that's the same as 50% of the time above 0.5 volts and 50% below 0.5 at the O2 sensor. However, if you can get the signal to swing back and forth, that's usually pretty good.
posted by 192.249....
, Thu, 10 Feb 2005 13:39:01 <-- Viewing This Message
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