Usually starting is the problem.......

[flob...@gmail.com]

...... but not today, stopping the engine is the problem. Fired up the saloon today, first time for a few weeks, no problem starting but when i turned the key to off the engine continued to run and did so on subsequent start/stop tests. Only clue is ignition warning light comes  on when key turned to off. Checked the switched live feeds and they had 5volts on them with engine running and key out, enough to hold the relays i use to feed ignition/fuel pump etc. So where is it coming from? As it's only there when the is running the alternator looks a good place to start, but how or why can it cause the problem? 

Anyone know or have alternative theories/ideas?

Russ

[Jim Hearne]

I’m assuming it’s an injection engine.

What is happening is that when you turn the ignition off, power is flowing from the alternator warning light pin ,  through the alternator warning light and supplying power to the ignition / fuel pump relays.

This doesn’t happen on  carbed car as the ignition coil is powered directly from the ignition circuit so when you turn the ignition off you can’t  supply enough power through the ignition warning light to keep the ignition coil running.

On the injection cars everything is powered from the battery via the relays so doesn’t need much to keep the relays powered.

 

There should be a diode in series with the blue alternator warning light wire near the alternator to stop this problem.

Maybe the diode has gone short or maybe in the past you have always had something else switched on that draws enough extra power from the ignition feed circuit to drop the voltage low enough for the relays to open and stop the engine, heater fan maybe ?

 

Jim

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[flob...@gmail.com]

Thank you Jim that sounds a distinct possibility, the car is running carbs but the ignition is edis/megajolt, so the electrical system should behave as fuel injection car. I will try turning on something  electric that is not powered via relays and see what happens. I take it the diode should go in the switched live line to the alternator? or is it the ind line?

Russ

[flob...@gmail.com]

Sorry Jim, stupid question, you quite clearly say where the diode should go.

On Wednesday, March 15, 2023 at 4:58:04 PM UTC Jim Hearne wrote:

[flob...@gmail.com]

Found a potted diode with spade connections in the 12v electrics bits and pieces box and fitted it today. Everything as it should be now. Thought for a moment that the fault had gone when i moved the car this morning but then realised i had my foot on the brake pedal when i switched off the ignition; perhaps this why i had not noticed the problem before.

[Jim Hearne]

Good news.

I was waiting for you to ask which way round the Diode goes.

As long as the warning light still come on with the ignition on but the engine not started then it is the right way round.

For those technical people, the diode should should have the cathode on the alternator side and the Anode on the warning light side.

 

Jim

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