Hi All,
A friend is getting intermittent DTC errors when his ´97 XK8 Coupé is hot and he suspects his alternator may be faulty as he has already changed his battery.
What level of voltage would be expected at the battery terminals with the engine running and with everything turned on (A/C, lights etc.)
Many thanks!

 

Hi,

With a properly functioning alternator, and the system at full load and idle, the voltage should be 13.0Volts to 14.2V, and increase with engine speed to 14.2V. If you don't see this, further examination of the alternator and connections would be warranted.

All the best,
Jerry

 

Hi Jerry,

That is what I suspected.

Many thanks.

 

Here’s the excerpt from the Workshop manual how to test from a cold start.




Before replacing the alternator best to first try cleaning clean all the electrical contacts at the rear of the unit first.

Also the electrical voltage regulator can be removed from the unit for a rebuild but this tends to be a lot of work for not much cost saving compared to R&R of the entire unit.

Bear in mind that earlier X100s also had a separate suppression module located under the air box.

 

Hello again,

My friend has just called me to say he has changed his alternator and that he no longer gets any DTCs and the battery voltage seems fine.

However, he has noticed that his idle speed is 670 - 680 rpm, which seems low and that his headlights dim when the car is idling.

What would be a `normal´ idling speed and would you expect the headlights to dim at this speed? Is the idle speed adjustable?

Many thanks.

 

I have an early '97 coupe and it idles at around 660 rpm. I've never noticed the headlight dimming even with the AC on.

 

FWIW, people have many times reported poor results after replacing alternators recently, and having to redo the job with other parts. Folks seem to have had a lot better results rebuilding their original unit instead. Denso again seem to come across as the more trusted manufacturer.

Best of luck.