My girlfriend’s car needed a jump and my 2002 XKR was the only other car available for jump duty.

I was worried about unknown strains being put on the XKR’s electrical system and reasoned that the best path would be to jump her car with the Jaguar not running and ignition off .

Did I do right ?

Z

 

Usually its done with the car running. The only important thing is to make the last connection to the engine block of the failed car not to the battery terminal in case you get a spark and blow the battery up ...ever seen one go ? very loud and messy .Usually blows the whole end off the battery . Never make the final connection to your battery!
Once connected raise the rpm to a couple of thousand and start the bad car . Take cable off the engine block first. Re charge with a mains charger over night . The alternator will not fully charge the battery its voltage is too low.

 

That’s the way I would jump a car normally. But the delicate nature of the XKR’s electrical system had me spooked. So I was fearful of putting any “load” on it with engine running and all the modules active.


Z

 

who told you it was delicate…this is not a eurotrash car lol

https://m.littelfuse.com/~/media/electronics_technical/application_notes/varistors/littelfuse_suppression_of_transients_in_an_automot ive_environment_application_note.pdf

https://media.monolithicpower.com/mps_cms_document/c/o/cold_crank_to_load_dump-primer_ver1.3.pdf

the only thing that could hurt itself is the car being jumped with its own alternator, and this never happens in the real world

 

Z ray asked if he did it right ..no need to attack him for checking out a procedure

 

Always interesting variations whenever jump starting is discussed. The handbooks for both my XK8 and X type state:

Do not run the jump start vehicle’s
engine when boost starting a
Jaguar vehicle. If the jump start
vehicle’s engine is running and
the jump leads are disconnected,
damage to the Jaguar vehicle’s
electrical system will result.

 

Z:
I think that it may depend on ones risk level.
I would have done as you did, except that in addition, I would disconnect the battery from my XKR. (I keep a 10mm wrench handy for such)
Xalty provided an excellent attachment on how the industry is protecting our delicate electronics from transients as he put it "that could hurt itself".
Not taken into account are my getting my grubby little hands into the mix. In the mid 70's, I zapped a $180 (high dollar then) electronic device on my dime and immediately realized that my near zero voltage source had a much higher transient voltage component. Steve (WhiteXKR) warned me years ago on this forum about the dangers of using non-Jaguar relays which may not have transient protection for our electronics. I trust him and his excellent Jagwrangler offerings.
Like me, I know that you also use a battery tender. That is probably indicative of the top of my risk level.

 

Z if it matters, the way you did it is how i was taught by an electrical engineer and a GM engineer. They both said that it is ok for any car to be running to help build a charge in the dead car for a while, however they strongly recommended turning off the jump car for the actual start event. Old cars, protects the alternator diodes, and newer prevents a surge back to the jump car's modern electronics if the dead car's regulator sees a shorted battery or very low battery and does not immediately read the voltage from the jump car due to cable resistance.