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Old 02-12-2010, 03:17 PM   #18 (permalink)
jfitzpat
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Quote:
Originally Posted by puddleglum View Post
I won't begin to debate this with you because you obviously know far more about it than I do and I've been wrong before. But, for the sake of curiosity, I will check how long it takes my car to get to CL from cold and see what the temp reads when it does. I was under the impression that the O2 sensor in my car did start to heat as soon as the key was turned on or at least as soon as the engine started. Maybe I'm wrong. Now you've got me curious.
No, not heated until condensation is cleared. And not CL until all the indications are for in range combustion and the O2 sensors are at temp.

As far as first, you should generally be CL long before you see much in terms of ECT change on most newer vehicles. In older vehicles, ECT was a thermal switch. On, normal, off, timing retarded and richer for cold operation. Then it advanced to a thermister, with multiple steps of enrichment, etc.

But think about what "Closed Loop" means. It means that the ECU is targeting lambda 1.0 for emissions purposes, so no extra fuel is involved. So, if the system reports "closed loop", the ECU has made the decision for normal, not cold engine, operation. On some vehicles, you can pretty much count on this being a specific ECT. But on many new vehicles, this is not the case. They are making the decision on a combination of other sensors instead of just accumulated radiant heat.

The problem with relying just on ECT is that energy goes three places, work, CHT, and EGT. EGT is put to use in driving emissions systems, and work moves the car. But CHT is, beyond a certain, fairly low, threshold, wasted energy, and destructive, since high CHTs lead to things like abnormal combustion.

So, modern engines try to minimize CHT with lots of techniques, including sophisticated timing systems, which move peak pressure. So, in cold weather operation, you've got ambient temp (and many modern ECU's have AAT even if there is no outside air temp in the cabin), which impacts how much air cooling is occuring, and ignition system trying to hold CHT down, and a cooling system which is meant to carry excess heat away, but whose efficiency is also impacted by AAT and air mass... (and so on)

If the decision was just a simple case of 'heat X has found its way into the coolant', there would be cases where vehicles stayed open loop for no valid reason, which would be bad for emissions.

-jjf
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puddleglum (02-13-2010)