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MG MGF Technical - Really strange eletrical problem 2002 MGF

A STRANGE thing happened with one of our MGF s - a 2002 - it stopped charging, ign lamp just glowing and we put in a recon alternator.

After a trial run all was ok, BUT when he started it up with a high rew (4-5000rpm for a second) the ign lamp started glowing again. Stoped it, started it and engine management lamp turned on, so did ABS warning, electric steering colum assistant stoped working and no ign warning lamp at all. But the really strange is this,,, as soon as the rew went below 2000rpm all went back to normal, on higher rews same thing happened again and again and again....

We put a digital Voltage meter onto battery and the alternator charged all from 13 upto 17 Voltage ref to engine revs and its infact correct as headlights were "flashing" accordingly!

This was just tried for short periods, but suddenly alternator stoped charging, and all went back to "normal" apart from no charging!(ö)

WHAT IS / WAS THIS, anyone had this kind of problem ever ???? Was it a faulty alternator regulator that made the car behave like this?? I guess its a inbuild thing, its a late MGF with a mgtf like 85A Bosch alternator! Was it the sudden rews that killed the regulator making the alternator send "unregulated" Voltage making all kind of fuss for the car electrical system?? Or what???
RN Roar

given that i am always reaching maximum revs thru gears in normal driving,and that the engine temp should not interfere with the alternator output, and that the only time ive seen the no charge light come on when the engine is running, has been when one of the alternator mounting bolts came off, and the belt slackened.. ive no idea as to the cause of your fault.. except to think that overvoltage, or unregulated output, - i.e AC not DC, would damage components that are DC voltage specific.. such as components on the ecu.. but even that is unlikely given that the battery would hold the circuits DC...

something iffy about the alternator i think.. and i would fit a new one.. thinking that removal by substitution is often the only way to cure faults that have no obvious cause..
N.J. Simon

Would aggree with N.J. Simons opinion.
We just had a similar case in our German Forum.
May be you can source the regulator only and change it.

It's a widely used type of regulator at late MGF/TF.
Have a look at the post in German and the pictures.
http://www.mgboard.de/viewtopic.php?f=2&t=7631&start=0
Page one and page two.
I.e. see for regulator *cargo 139925* with google.
Dieter

This thread was discussed between 02/07/2012 and 08/07/2012

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