Are there any PCM signals that only go active once the car is running?

I am designing a push button start for my car and need a way for the circuit to know that the engine is running to disable the starter.

thanks

 

The PCM indirectly senses that the engine is running from several indications: RPM from the crankshaft position sensor, oil pressure, manifold absolute pressure among others. However, there is no discrete output that says running = 0 (no) or running = 1 (yes). In fact when you crank the engine either directly by the ignition switch or remotely via a remote starter, you have to decide when to release or disengage the starter.

Steve

If you had a vacuum operated switch that opened when the vacuum exceed a certain amount (like 20" Hg), then you could have that switch in series with your remote starter switch. Why not just buy a commercially available, no frills, remote start switch kit?

 

An oilpresssure switch such as the ones used on ford vehicles for the oil pressure gauges, that turn on at 6psi would be one method, but it would just work for preventing accidental pushing of the starter with the motor running, not to stop the cranking circuit from running the starter once the motor is running.

If you are really really good with electronics and programming, there is a "time running" function available through the OBD2 port, that could be used, but it is probaly far too complex for what you are looking to do.

Ryan

 

That takes some of the fun out of it. The circuit I am building will be an onboard system, not remote start. Push the button once and the car automatically starts. Push the button twice and the start circuit is disabled leaving you in IGN ON for programing and diagnostics. Tap it when running and the engine shuts off. I have it all figured out except for disengaging the starter once the engine is running on its own. I have it on a 3 sec timer to stop cranking if the engine never runs for whatever reason, but really need it to stop cranking when it does start. I was thinking of using the MAP voltage, kind of similar to your vacuum idea.

 

The easiest way is to use a vacumn switch. There will still be a window where damage could be done, though. I have one that you just put a t adaptor on and go.

Hell, you can damage you car with a normal key switch!

 

How long after the car is running on its own does vacuum build up?

 

You get some vacuum during cranking.

 

Makes sense otherwise no air would get into the cylinders for combustion.

How would the vacuum compare when cranking to when at idle?