This is probably already revealing how old some of us are, but we remember that we had to start our cars by turning the key and waiting to hear the engine “catch”. At that point you knew the engine was ok to proceed, and if you stopped turning the key it wouldn’t die.
How does the starter today (push button) know all this, and it never seems to get it wrong? I have never heard a push button starter fail to get it right unless some other issue like dead battery, etc. (and btw, today’s engines seem to have so far fewer issues like we used to have)
In: Engineering
Well, the ECU knows when the engine is running. It keeps the starter going until it senses that the engine is running.
If you disconnect the fuel line from the engine and hit the push start button, it’ll keep trying to crank the engine for a while.
There weren’t computers in cars back then, but every car has one now. In a modern car with a push-button starter, the computer knows exactly what is happening with the engine (and pretty much everything else), so it cuts off the starter once the engine starts turning over.
There are tons of parameters that are monitored by the ECU. Manifold pressure O2 and rpm would be three things that would tell the computer the engine is running.
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the p01 computer in 99-03 chevy trucks looks for a crank/cam sync minimum run time vs crank speed.
i would assume they just added more stuff like airflow vs time or crank speed.
i reckon it’s probably all crank speed based since your average idle rpm is about 2-3x crank speed
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Part of this is fuel pressure. This is controlled more exactly now. Ten or fifteen years ago the car would not pressurize the fuel system right away. It would take a second or so to build up. Fuel pressure close to instantaneous now so less time is needed to crack the now brushless starter.
I am not a mechanic, but isn’t there also a mechanism that disengages the starter from the flywheel once the engine has begun turning faster than the starter?
The system would be able to detect that disengagement and know it can deactivate the starter.
Tach signal.
I left this simple but accurate answer but apparently it lacked enough words to be accepted.
There’s a signal from the engine called tach signal. Remote starters use it to know when to stop cranking. Push button starters will use the same signal. There’s lots of different data streams in a modern engine but tach signal will be the one used for the scenario in your question.
You didn’t always need to keep the key in the “start” position. Some Mercedes for example, you would turn the key to “start” then let if go and it would keep cranking until it started, kind of like the “push button” ignition now.
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