ECU Start Signal

I know the start signal is supplied during the operation of the starter motor but what does the ECU do with that signal? Does it modify or control the fuel pump operation?

Thanks, Andy

Hi Andy,

yes it does use it to run fuel pump and injectors no matter what trigger contacts say. There are further changes but they differ from ECU to ECU.

Thanks. I'm not sure I understand exactly what is happening though.

When the starter is turning the engine is rotating and the distributor will be rotating, so the trigger contacts will be operating, although at a low engine speed.

What does the start signal do exactly if the trigger contact pulses are present? What is the deficiency in the trigger contact pulses that the start signal overcomes?

Thanks, Andy

Hi Andy,

starter revs are nor enough to convince ECU of a running engine. It would normally not activate fuel pump. That is why fuel pump is activated for 1-2 seconds with igniton ON and then also when starter runs. Trigger cams are ignored during start. Only when engine runs they are taken into account by ECU.

An engine with not working TC will start from coldstart valve and ECU. But as soon as starter is off, it will die. Pin 18 is also used for some other function blocks. But that differs from ECU to ECU.

Thanks. I just tried a quick test. Start signal is at 0V (so no cranking), engine is rotating at 50 RPM.

I see that the trigger contacts are generating the pulses, the fuel pump is on and the injector pulses are being generated.

So it seems the ECU believes the engine is running fast enough to turn on the fuel pump at this low speed?

The start signal is only for a non-working trigger contacts? What condition do the trigger contacts not work as they are just mechanical based on the rotation of the engine?

Thanks, Andy

Hi Andy,

no all this is only to help the engine start.