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Re: How vital is an O2 sensor to a Saab's performance? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 11 Jun 2004 08:17:25
In Reply to: How vital is an O2 sensor to a Saab's performance?, B Hayes, Thu, 10 Jun 2004 08:43:35 Members do not see ads below this line. - Help Keep This Site Online - Signup |
If the ECU has determined that the O2 sensor is failed, it will use a default value to schedule fuel. In general, this value would insure a richer mixture.
Probably minimal performance (e.g. accleration time) impact. The engine will run a little cooler with a richer mixture, but probably not enough to notice. You probably still need a thermostat.
Downsides - (1) gas mileage; richer mixture is using more gas. At today's prices, that's no bargain. (2) emissions - a richer mixture is producing more emissions, usually HC and CO. (3) Carbon buildup - shorter spark plug life, and carbon buildup on valves, plugs, pistons and cylinder heads. In the very short term, not a big deal. Over time, this can result in stuck valves, increased compression ratio leading to knock, and shorter spark plug life.
So in the very short term - a few weeks - not a big deal. I would fix it.
However - be warned that an "O2 Sensor" fault code DOES NOT mean that the O2 sensor is bad. All the code says is that the sensor output is out of range. The sensor reading is stuck at rich or at lean. If the sensor says the mixture is lean, the ECU will add fuel (richen the mixture). But the O2 sensor only has limited control of richening (or leaning out) the mixture. If you have a vacuum leak, the sensor will say the mixture is lean, and it'll command more fuel. But it can command only so much - if that isn't enough to get the mixture back into 'normal', the sensor will still read lean, and that's the truth. But you'll get an O2 sensor fault.
So a vacuum leak can cause lean running that will give you an O2 sensor fault. A stuck fuel injector or leaky fuel pressure regulator can provide a rich mixture and a sensor fault.
Check the spark plugs AND measure the O2 sensor output. This takes some troubleshooting. Otherwise, you may change the O2 sensor and the problem will still be there. Fault codes are a start to troubleshooting, not the end.
posted by 192.249....
, Fri, 11 Jun 2004 08:17:25 <-- Viewing This Message, Thu, 10 Jun 2004 09:33:10
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