Electrical Issues and Stalling

Greetings! OK so yesterday I picked up my XJS - 1990 V12 convertible is gorgeous nick. I have previously owned a 1995 4.0 Celebration and a 1994 V12 convertible (both face lifts) but been away from Jags for a good few years but now I’m back!

Anyway - the V12… its a 5.3 and the engine starts and purrs - absolutely lovely. The problem occurs when I am setting off. I select D and the engine is happy. As soon as I touch the accelerator to set off, the engine cuts out. The only way I can get it not to stall is to jab the accelerator to give it some revs and even the revs drop momentarily before it revs up. When decelerating for a junction and then accelerating, the problem doesn’t occur. It only happens when I set off from standstill.

The other issue I have is electrics. The indicators work when they want to! Quite literally I will indicate left and I can hear the flasher ticking and then randomly they will just stop. At the same time, other things stop working, such as electric windows. I’ve not had a chance to check fuses yet but wondered if anyone had experienced anything similar and whether fuses are likely to be a factor? I have not done any more research yet but thought I would ask.

I wonder if the stalling issue is related to the electrical issue?

Cheers

Sean

All of your electrical issues could be related.
Check ground connections. When going into gear and attempting to accelerate engine torque movement may be causing ground disruption.
Definitely not a fuse issue. Check engine block ground jumper.

Sean,

As for the electrics, fuses often cause problems.
Remove each fuse, check if they are broken or loose and bend the holders to be sure they make good contact.
Grounds as well as previously mentioned.

As for stalling, is there a difference if the engine is cold or warm?
First thing I would check would be the Throttle position potentiometer.
Ignition advance, ignition amplifier, plugs and wires would be the next.
Details in the Book.

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Thanks for the suggestions - I will do some investigations this weekend and report back

Cheers

Sean

Re the flashers. Take the hazard switch apart and clean it. Everything goes through that switch and internal oxidation of the contacts will make it do bad things.

Re the shut off during take-off… hmm… check to make sure the vac signal to the ECU from the crossover pipe at the rear of the engine to the ECU in the trunk holds vacuum. For giggles electrically clean the Coolant Temp Sensor connectors (both sides). There… IS some small possibility that the front crank position sensor is ailing, and confuses the Marelli ignition ECU when trying to pick up RPM from idle, but if it revs from idle in neutral I’d discount that — unless it’s a wiring thing (which has happened where moving said wiring affects whether a car will start or not)…

TPot? Eh… on these cars it can be unplugged and the car will still run - just won’t be as responsive (think electronic carburetor accelerator plunger + a little more)… on an AJ16 X300 it’s a little more sensitive - will run - but if it gets a bad input from a TPS it’ll break the EFI. Not so much on the V12 to my knowledge/exp.

~Paul K