Xantia TD Electromagnetic Advance

Post by **CitroJim** » 16 Sep 2006, 22:10

My Xantia has the Bosch pump with the microswitch and electromagnetic advance arrangement.

What, precisely, is its purpose in life?

Under what circumstances does this little lot operate? I did some tests and found there is +12V present on the advance solenoid at all times, whatever position the microswitch is in. I checked the switch by disconnecting it and found it to be operating normally. I.e. short-circuit on idle and going open-circuit as the cam operates the switch.

I disconnected the wire to the solenoid and if I dab it on and off the solenoid I can hear a slight (but only a very slight) change in engine note. I can also hear the solenoid operating with a light click if I put my ear close enough.

I've searched past Posts but have not found any answer to my question and the BoL does not show this on any wiring diagram.

Many thanks

Kowalski · Post by **Kowalski** » 17 Sep 2006, 09:51

Is the advance on the older bosch pumps for cold starting / warm running?

KevMayer · Post by **KevMayer** » 17 Sep 2006, 10:19

Does your engine have ECU control. If it does then the folowing probably applies. If not , then its just a bit of interesting info.

For a Bosch AS3 pump :-

I read somewhere many moons ago that the supply to the timing solenoid has a pulse modulated DC supply.

I read that the solenoid is progressive so that it operates in proportion to the voltage applied. The ECU gives it effectively a variable voltage by modulating the 12 volt signal. eg. if you have full 12 v applied for the whole period then the solenoid sees 12 v as the average voltage. If you apply 12 v for only half the period the solenoid only sees an average of 6 volts and doesn't open so far. 12 v for a quarter is thus seen as 3 volts and so on.

Like you, I couldn't understand how there could be any variaton if 12 volts was applied all the time. But the modulation process explains how it works.

Now, I can't remember exactly where I saw all this. I know that this DC modulation is used on controllers in industry but I'm no expert and hopefully, if this is a load of rubbish, one of our friends here will correct me.

cheers, Kev

Post by **CitroJim** » 17 Sep 2006, 19:40

Hi Kev,

No, not an ECU controlled pump. Just a straight mechanical Bosch with this bit of electrickery on it. 8)

Strangely, SWIMBOs 405TD of much the same vintage does not have it although it has a suerficially identical looking Bosch Pump.

Dave Burns · Post by **Dave Burns** » 17 Sep 2006, 21:42

Lets have a picture.

Dave

Post by **CitroJim** » 18 Sep 2006, 07:40

Will put one up when I get home this afternoon...