We have a 1985 XJS V12 which was brought here on a rollback. It initially ran badly with gas coming out of the exhaust. It was deemed a large project and put on the back burner while I gathered some new or refurbished parts. Two years later, it's back in the garage and becoming worse than a cancer. First of all, a mouse moved in and chewed through some of the wires. After fixing those wires, there is no pulse for the injectors. If the key is removed from the ignition, the interior lights and dash stays on. The only ignition coil is a large square one, not 2 cylindrical ones and there are 6 wires not 2. The 6k resistor specs out at 5.94k, but when the battery is connected, the 12 volts go away. With the original British-Leyland manual and a Haynes manual, nothing looks at all like what they are showing or saying. We are at a loss. Has anyone seen anything like this? The manufacture date is Aug 1984.

 

Likely the dual dulcimer coils were replaced with the more modern available square single coil replacement (similar to if not idenical to the Marelli coil used on the later car). Re the management system, always start with the ignition first. It is separate upstream system of the EFI system. The EFI system is depending upon getting an RPM pulse in order to know to perform injection (which comes from one of the 3 way splits of the negative control side of the Lucas AB14 amp box (really a GM HEI 4 pin amp). The coil and amp get ignition power. The amp box controlls coil charging via a wire to it's negative side (one of the 3 way splits inside the box). The other two ways go to the tachometer, and to pin 18 of the EFI ECU via a white shielded wire through resisters inside a silicone bob inside the amp. No RPM pulse (bad wirng/box/etc) no fuel injection. That said the EFI ECU WILL command a single burst out of the injectors if the Wide Open Throttle switch (WOT) is triggered with key on by turning the capstan to full open (a good way to know the EFI ECU is in OK shape), but won't perform running injection w/o that RPM signal. The EFI ECU will also power up the fuel pump for a few seconds with each key-on but WILL NOT re-activate the fuel pump relay (provide a ground for it) unless it sees the Starter Relay +12V signal and ongoing RPM pulse. Get the 1987 electrical diagrams from JagRepair.com (free) as they're so close to the 1985 setup as it makes no difference.

For your lights staying on you probably have a stuck relay, or one of those mouse chew-throughs has created a groudn short that keeps a relay active.

Re your resistor specs are you speaking of the Power Resistors pack? (your spec is close enough). +12V should always be present to the injectors via the main relay which makes it present at the resitor pack AND to the EFI ECU for grounding (how the injectors are activated by the ECU). Or are you referring to testing one of the two resistors in the silicon bob inside the Amp box (2 different specs). Also a single ignitoin coil should have a 0.6 Ohm resistance as the dual setup had 1.2Ohms each for 0.6 Ohms in parallel.

~Paul K.