Alternator only works with sidelights on

[Skifo 0]

Hi everyone, I'm new here but having a problem with my wife's 451, 2008, petrol. She broke down going to work 3 weeks ago and I've figured out that the alternator is only providing power when (at least) the sidelights are on. 

 

At engine idle it provides around 14.4v, but any higher than idle i only get 12.7v. Also this only happens approximately 40 seconds after the engine is started. As soon as i turn the sidelights on while engine is higher than idle, it goes back up to 14.4v. Nothing else affects the output, air conditioning, radio, fan, rear window heating have no affect on it.

 

I changed the battery as it was old and 2 of the cells weren't looking good and one was a bit low. I've removed, inspected and cleaned the alternator. It looks good, brushes are fine. (I can't really check the regulator/diodes though).

 

I've checked all the fuses and wiring from alternator to battery and all the grounds i can find. Yesterday i removed the SAM to see if anything looks odd/loose/burnt in there, but that looks ok too.

 

I was thinking it could be a relay due to it only happening after 40 seconds of the engine being on...

 

Anyone have any ideas?

 

Thanks

[Dangem 0]

Hi Skifo, did you find the fault with the alternator charging ?  I have the same model and year with exactly the same fault. It seems like a timer issue. If I switch off and on above 1500 rpm it will charge again for about 40 seconds. No charge when accelerating but charges on overrun. Driving me mad.

 

Mike

[Skifo 0]

Hi Mike,

I got a little excited when I got the email that someone replied to my post. I thought someone would have the answer!

I haven't really had much time to investigate any further really. I bought a small voltage meter which sticks directly into the cigarette lighter socket to keep an eye on it while driving. I just turn the lights on each time I use it. I do sometimes turn them off in the hope the problem will automatically disappear though!

 

I'm also busy with the car not always going into reverse, which is more of a problem.

 

It could be the alternator, but don't really want to buy a new one when it might not fix it...

 

I'llpost something if I figure it out though.

[Huronlad 186]

The alternator in my 2011 failed this year.  With the new aftermarket alternator replacement I noticed right away  the Ultragauge in my car now starts up almost instantly.  It shows the alternator working from idle and is steady under all conditions.

[Dangem 0]

Hi Skifo, sorry still no luck in finding  an answer. I thought it was the alternator, but am now convinced it is the control from the ECU not powering the field winding (should be pulsed). I am looking at the throttle control to the ECU as the fault seems to be related to the throttle position. Main problem is finding a good circuit diagram ! Anyway, just fitted a rear wheel bearing kit to pass MOT.

 

I will let you know if I fix it. Where are you in Italy, love the country.

 

Cheers

 

Mike