Ive come across another strange problem on my car, Ive started a new job and I have to go for a 20 min drive down the motorway every day, When I get to work or get back home the idle is really rough and any lights that are on go bright and dim, The head unit turns on and off too. It only does it when I drive on the motorway though.

 

Is the battery being charged though? Has it gone flat yet?

 

Battery doesnt go flat. Drove home just now, Had to drive steady cos of the weather, It was ok when I get home, Ive also left it idling for about an hour and it was ok, It only seems to happen when I give it some thrash

 

Do you have a multimeter so you can do a few tests?

 

I do indeed

 

Check this out:

http://forum.fordsierraclub.co.uk/viewtopic.php?t=18853

 

Have you got the heat shield on the back of the altenator????

Sounds like the altenator is getting too hot from the heat soak from the manifold/turbo

Fitted a re-con alt on my saph last year,lasted 2 days,had a good blast and it melted the regulater off the back of the altenator

This was before I realised there is supposed to be a heat sheild on the rear of alt

Made one out of an old piece of turbo heat shield now

 

It could be that, The alternator is on the back of the engine and the turbo on the front

 

It could be that the diode pack has failed and is letting current flow through the alternator the wrong way.

Just a thought...

 

Sorry m8,thought I was reading posts in the Cosworth section