Thanks for all the previous replies as to how these work, but I have another question regarding the failure to restart after a cold start then stop.
As the Lambda sensor only works when hot, and any signals from it are disregarded until then, what tells the ecu not to let the vehicle start due to too much fuel in the exhaust?
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Most of them contain a heater.
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Thanks for raising the question Dave, it's something I have often wondered about and look forward to some advice from the experts. Also, what does LAMDA mean. Is it an acronym for some long technical term or, did Mr Lamda get hold of the idea first ? (tongue a bit in cheek there)
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Why it's called a lambda sensor...
If you plot the concentration of one pollutant in the exhaust gases against the fuel/air ratio, the carbon monoxide and hydrocarbon concentrations decrease rapidly around the stochiometric point, whereas oxides of nitrogen increase. This line makes the shape of the Greek character lambda. That's why the sensor is called a 'lambda sensor'.
Andy
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Thanks Andy and, yes, I really wanted to know because of a bit of a heated argument a few weeks ago with someone who professed to be a bit more knowledgeable than he really is on these matters. Armed with your information, and dropping it casually into the conversation, I am going to raise my motor "cred" enormously. Mind you, that cred was already quite high in the days of the Ford side valves but, when they started to bring in all those overhead camshaft thingys and abandoned 6 volt electrics, I kind of lost touch.
Thanks again
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Andy
Yes, and at the point where stochiometric combustion occurs lamba = 1, which is the figure the car should register at MOT time (Usually =/- 3%)
Regards
John
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Pete, I know they contain heaters these days, but that only speeds the response, and until it gets to temp, the ecu disregards it. So what tells it it is over fuelled?
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Going to your original question there isnt anything that TELLS the ECU 'not to fire up'. It is just an unfortunate set of circumstances that results in a flooded engine. On some cars, notably GM, they have a 'clear flood' facility if you do inadvertantly flood the engine say by running it for a few seconds then switching off then restarting a few minutes later, initiated by depressing the accelerator to the floor then cranking the engine until it starts. This action has the effect of disabling the injector(s) clearing the excess fuel until it starts. At this point the management system comes back in and runs normally. The other reason for some engines reluctance to fire up after a momentary cold start is sticking valves and or lifters which pump up excessively holding the valves open. Causes for that is short journeys, cheap petrol, lack of servicing etc....
Funny, I have just realised that we used to clear flooded carb engines the same way, progress huh!
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Going to your original question there isnt anything that TELLS the ECU 'not to fire up'. It is just an unfortunate set of circumstances that results in a flooded engine. On some cars, notably GM, they have a 'clear flood' facility if you do inadvertantly flood the engine say by running it for a few seconds then switching off then restarting a few minutes later, initiated by depressing the accelerator to the floor then cranking the engine until it starts. This action has the effect of disabling the injector(s) clearing the excess fuel until it starts. At this point the management system comes back in and runs normally. The other reason for some engines reluctance to fire up after a momentary cold start is sticking valves and or lifters which pump up excessively holding the valves open. Causes for that is short journeys, cheap petrol, lack of servicing etc....
Funny, I have just realised that we used to clear flooded carb engines the same way, progress huh!
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And how long do these things last? I recall an article in a car mag a couple of years ago saying that they could only last 30/40 k miles.
Thoughts/comments/observations anyone?
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