Is it this that detects too much unburnt fuel in the exhaust as a result of cold start then stop?
If so, how does it detect it? I thought it detected oxygen, not hydrocarbons.
Also, if it packs up, then engine can still run, so how does it tell the ecu to shut down firing?
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You can short the sensor out and it will run no problem
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If you short out the lambda sensor, the ECU will go into open-loop mode and use a fixed (pre-programmed) fuel/air ratio. It does this to try and reduce emissions. The result is that performance (and fuel economy) suffers and you get a permanent 'Service Engine' light.
The signal sent to the ECU from a working lambda sensor alternates between about 0V and ~6V and if the ECU doesn't see this change, then it assumes that the sensor is faulty.
The reason that some engines will not start after a short on/off period is that the ECU software remembers that the last time it was started, the engine never reached sufficient temperature before it was switched off again.
If you REALLY have to:
Removing the fuse for the ECU for a few minutes will reset it and allow you to start the engine but will damage the cats.
Personally, I'd recommend that you go back in the house, brew another coffee and give it 20 minutes or so.
Kevin...
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Yes, lambda's detect oxygen. Its job is to ensure a stoichiometric mixture, ie an air fuel ratio of 14.7:1 (And I've just got back from the pub, -Abbot ale) by mass. If an engine is running lean, there is too much oxygen in the gasses, and the sensor will tell the ecu to richen it up a bit, and vice versa. It works by comparing the oxygen value of air to the oxygen in the exhaust through a ceramic porous component. these can often become dirty, causing a slowness in the reaction time and subsequent problems. Andy is right that they cycle between 0v and about 2 in my experience. 6v seems a bit high. The response time is about 1/2 second. If a 14.7:1 ratio is maintained, perfect combustion is possible, and the cat stands a chance of reducing any unburned hydrocarbons, CO and NOx to minimal quantities.
Regards
Mike
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Mike,
I think Andy meant 0.6v, not 6v !! Actually the normal switching voltage should be between 0v and 1.0v, but in practice it is more like 0.1 - 0.9v.
2.0v is very high for a normal Lambda Sensor. Some Ecotec systems employ a slightly different Lambda principal, with voltage switching between 0v and 5.0v
Regards, Adam
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Adam, You are quite right! Thanks for the courteous reminder. I should know better really.
Regards
Mike
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Thanks Mike!
That's gone in "my documents". I suppose it would be a bit steep to ask if a Jap cat would be exactly the same animal?
Regards, Tomo
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The Lambda or HEGO(heated exhaust gas oxygen) sensor is switched off by the module for the cold start-it starts operationg when the extra fuel used for starting is switched off.
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