My SLR has a Racing Pulse - Voltage Regulator Problems

[Mike Scott]

Hi Guys,

I’ve searched the archives on voltage regulators and charging problems but haven’t found anything like the problem I have, maybe Chris W or Andrew (Soupy) may be able to shed some light .

The spec is a 98 SLR with VHPD engine, a Rover branded Magnetti Marrelli alternator (can’t see the model number) and Rover MKC104521 ECU. Having read the archives they suggest the voltage regulator is in the ECU, however my alternator only has 2 connections, a thick brown wire on B+ and a thin brown with white stripe wire on D+, there is no stud (or wire) on the W terminal.

 

Now for the strange part

Engine off battery volts = 12.6V

Engine off lights on battery = 11.9V

So the battery is OK

 

BUT

When the engine is running, throughout the rev range, and with the lights on or off, the battery voltage oscillates between 14.7V and 16.6V at about 2Hz

 

This gives the lights a “racing pulse” when they’re on, as they beat at about 2Hz and is quite amusing to other drivers

 

Any idea on what is causing this? Could it be the diode pack or the regulator in the alternator 🤔

 

Cheers

Mike

 

 

 

[Jason Plato]

my lights pulsed when my chassis earth was a bit dodgy

 

here is C7 TOP

South Wales AO

[Mike Scott]

Hi Dave,

Thanks for the suggestion, can you tell me on your car which earth connection was a fault. Was it the engine to chassis strap, or some other connection 🤔

 

Cheers

Mike

 

 

 

[Jason Plato]

Engine to chassis was at fault.

 

but its also worth checking the other earth - under the scuttle on the windscreen wiper bracket .

 

here is C7 TOP

South Wales AO

[Mike Scott]

Hi Dave,

Thanks a lot for the pointer on the earth connections. I’ll check it out this weekend and let the Blatchat community know the results.

 

Cheers

Mike

 

 

 

[Mike Scott]

Hi Guys,

I just thought it was worth updating this thread in case anyone else sees this problem. I finally got to the bottom of my flickering lights problem, stripping down the alternator it was a loose connection within the regulator pack . So it’s always worth stripping the alternator and checking the internal connections before forking out for a replacement unit .

 

Cheers

Mike

 

 

 

[silver-7]

I traced my problem to the smaller of the two wires connected to the alternator

 

The tiny 6mm? bolt was loose

 

This caused the lights to flicker and the voltage to read from 11 to 15+ volts

 

hope this helps anyone else in the future

 

Alex