Having trouble after timing chain replacement on my 2000 XJ8.
I'm only reading about 12.4 volts on the battery after charging. Could this be a problem?

 

Should read 12.6 static and between 13.7/14.7 while the cars running/charging it via the Alt. Are you using a digital or analog meter?

 

Should run, but if it drops under load then expect problems.

 

Actually I'm using a digital multi meter and there is sufficient cranking amps available to turn the motor over fairly briskly but I wasn't sure if it was capable of supporting the engine management

 

Check the voltage while cranking. If it drops below 11 it may be a problem. If it were mine I would replace the battery.

 

You might also check the belt: may be loose; may have a bad tensioner.

My alternator went at 90,000 and 14 years.

 

You should get 12.7 volts on a battery when fully charged, not under load, and when all the surface charge has dissipated.

So there are some possibilities :

1) The battery didn't get charged fully.
2) The battery won't hold a charge.
3) The battery is under load.
4) You aren't measuring the voltage properly.

Have you ever checked the DVM against one of known good calibration? You should. I checked mine and it was only 60mV out. Pretty good, but it is possible that they can be much worse.

What exactly do you mean by "after charging"? How did you charge it? How do you know it was fully charged?