Today, I was going to get my XJR from winter storage. It starts emidiately, but after about one minute it stops just like the ignition was turned off.
After that, the starter was not working at all, not eaven a click in the relay. Everything else in the car seems OK, and the battery is almost new an fully charged.
I was thinking about bad ground, and got a very thick jumper cable from the ground on the battery, straight to the engine. Just the same: Nothing happened.
Anybody who have a suggestion for what could be wrong.
The car had some issues last summer also, with suddenly turning off some times. The ECU is just returned from refurbishing in a proffesional carelectric workshop.

 

Questionable work on the ECU ?

For the starter there is an enable through the engine ECU so look to be powered at all times by the 2 ECU power sources , right engine bay fuse box relay in the corner ( # 9 ) and the large # 5 right ECU controlled relay , this relay is controlled by the ECU and brings high current power back into ECU

small relay swap with the left engine bay fuse box relay in corner , only runs car horn

large relay swap with the headlights , fog , or A / C clutch of the same part # but in this case the relay is controlled by the ECU so to take that out of equation jumper the relay socket 3 to 5

These large relays can be easily be in wrong mounting position

Your starter relay not clicking splits your starter circuit in half pointing to the enables which your BPM sums up and provides a ground to close the starter relay

 

The starter sequence as it relates to the ignition switch which must have a good car frame ground on pin 5 of the IG switch connector

IG switch will give a ground path ( through pin 5 ) to close the right engine bay fuse box relay in the corner ( labeled as ignition positive relay ) , this first ECU power provides an enable for starter motor

IG switch will give a spring-loaded momentary ground path through pin 5 as a starter enable / command , this is your primary starter command asking BPM if it has the enables ( ECU , security , trans position and such )

The car side of the connector lifts straight up to remove from dash to bring work out to you , in your case no need to remove key barrel and if removable IG switch from barrel needing replacement no new key needed

Nap time

 

Thank you. I will check the relays and fuses tomorrow

 

This is your starter circuit for your engine / GM transmission combo like the V - 12

 

Thank you very much.