Hi, Guys

I am having issue to start up my XJR. already replaced the starter and battery but car still could start up without a battery jump. once I connect it to the jump box, it will start update right away and it runs just fine.

alternator is about 11 years old..any thought about it? I think it went bad

 

Where you connect the jump box ?

 

About the only way the alternator is affecting the starter voltage is if the internal to alternator voltage regulator is under voltage but you would think you would see a alternator / charge light

The large B + terminal battery cable output on the Alt should put out 13.5 minimum to 14.5 volts which the auto parts store can measure for you , a fully charged battery is around 12.75 volts

There are some connectors shortfalls that can affect the delivery final voltage from battery to starter :

Bus protection module ( mega fuses terminal nuts get loose and they do )

False bulkhead connector under hood , someone posted some good pictures lately

Never overtighten the battery positive post bolt , splits nut underneith