disable high RPM during warm-up phase??


Old 12-24-17, 04:01 PM
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disable high RPM during warm-up phase??

RE: Scion 1st Gen vehicles, but probably exists on many late model cars. During open-loop warm-up phase, the ECM delays upshift (automatic transmission), resulting in higher RPM, presumably to speed the warm-up of catalytic converter, thereby reducing pollutants and saving the environment. Back when I learned to drive, we were still using single weight oil, and were taught the importance of warming the engine, as most engine wear took place during this phase. While I realize modern oils have negated this requirement to some extent, nevertheless I can't help but think it's still beneficial to keep engine load and RPM low, at least until closed-loop (137* water temp., in my case) is reached, esp. during winter.

Does anyone know whether disconnecting a particular wire, or shunting a particular circuit might disable this function? While it might incur an emissions trouble code, it could always be re-connected before a yearly inspection. Or is this embedded into the ECM microprocessor, thereby only changeable by re-programming?

Or am I after a solution that's not a problem?

Thanks, and happy holidays to all.
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Old 12-24-17, 04:29 PM
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Its most likely to warm the transmission... The fluid pressures in the trans are most likely high due to thicker oil..

IMO leave well enough alone....
Old 12-24-17, 11:54 PM
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Mike is correct, it is more for the transmission than for the engine. Modern synthetic and even semi-synthetic oils lubricate quite well even at below zero temperatures. Just don't try making a six second quarter mile right out of the driveway and you will be fine.
Old 12-25-17, 07:57 AM
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presumably to speed the warm-up of catalytic converter
OP is correct, the initial few minutes of engine operation produces the most pollutants until cat light off, the min temp that the cat actually does something.

Idle is controlled by ECM, there is no way you will be able to disable that function.
Old 12-25-17, 05:14 PM
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There are scan tools out there for performance cars that can reprogram ecm but I would not do it for your application.
Old 12-26-17, 07:34 AM
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Can't really change it, It's baked into the chip.

You could manually upshift until it's fully warmed up.
Old 12-27-17, 11:56 AM
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You might need a new throttle position sensor, it is about $50. Quite a bit of the engine and transmission behaviours respond to the signals from the TPS. Replacing a TPS might be a relatively cheap "for greater certainty" replacement item.

But if the condition you noted has been there and unchanged for all time, then it is probably the way the car was designed for the emissions regulations. As long you are idling and accelerating fine without stumbling or acceleration lag, and otherwise enjoy a smooth running engine, you should leave things be.
Old 12-29-17, 02:59 PM
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Thanks, all. A solution in search of a problem. I shall carry on.

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