In the project I am working on, I am installing a number of modern conveniences and as part of the logic, do not want to enable power to them until the engine is actually running i.e. no power draw on battery until engine has started. Going through all the Fiero schematics, I cannot see anything that only gives a 12V signal when the engine is actually running.

Since I am doing an engine swap and custom digital dash, I do have a modern tach signal that I could run through a Dakota Digital SGI-8. This would provide both an output to the tach and try to use the high voltage output to drive a integrator to smooth to a DC signal that could be used to drive a base control relay.

Does anyone here have a working solution to the basic problem ??

If you have something that will provide a signal (12V output?) when it sees a tach signal, you could use that to fire a relay to feed the accessories. (Kind of like what you said...)

[This message has been edited by tesmith66 (edited 12-24-2012).]

Pull off of the fuel pump relay. With the exception of priming, it's only on when the engine is running. If you wanted to avoid the prime, just put a timer relay in there that times out at a period longer than the prime.

Look for the input voltage to be above 12.5v. Use two voltage divider resistors and send the signal to you analog input to your arduino. But the problem with that is you have your arduino running all the time unless you have the input to the arduino on a switched circuit. The same problem occurs if you look at the tach.

So what is wrong with using the switched voltage?

The fuel pump supply should work also.

Shoot, if using an arduino, that is an easy one. Feed the tach signal into an appropriate filter circuit, test for RPM above a threshold for X amount of time. If RPM is above minimum settings for said time, send power good signal or what ever you want. When RPM or power signal drops below a threshold, start a timer to shut down after a set time. I did something similar on a push button starter circuit. The device worked great. But alas, I am not a push button start type of person. This could be modified to do what you want with a minimum of hassle.

Keep tuning my friends.

Chet W.

[This message has been edited by chetw77cruiser (edited 12-24-2012).]

I am trying to avoid using a CPU. Can program in Basic so I could use a Coridium ARM processor. The fuel pump line is a possiblility. Typically how long does it take to prime ? and then does it shut off until the engine is started? I already have timed delay relays. Using one to delay the ignition start button enable so that an Accusump oiler can deliver oil to the cylinder heads before the engine can be started. Dash will display a 'Waiting to Start" while the timer counts down.

quote Originally posted by MCDUCK: I am trying to avoid using a CPU. Can program in Basic so I could use a Coridium ARM processor. The fuel pump line is a possiblility. Typically how long does it take to prime ? and then does it shut off until the engine is started? I already have timed delay relays. Using one to delay the ignition start button enable so that an Accusump oiler can deliver oil to the cylinder heads before the engine can be started. Dash will display a 'Waiting to Start" while the timer counts down.

2 second prime when ignition is first on, then it's off until you crank and start. Cascade a time delay relay off of the fuel pump relay set for something like 3 seconds and you'll never see the prime, and you'll avoid damaging the ECM if something goes awry.