I have been driving the XJS for a couple of weeks now with no issues. Today my daughter and I went to the store, her first time in the XJS, and it was going well. Of course she seemed less than interested as she was reading a book the whole time . Of course a few minutes into the drive the XJS just shut off! As in, running great rpm around 1800 then nothing, rpm dropped straight to 0 and we were coasting! I pulled to the side of the road and put on my hazards. Put it in park and tried to start it. Vroom! It fired right up! Decided to drive on figuring if it did it again I would go get the xk8 instead. It did perfectly the rest of the trip. Hmmmmm

 

One thought I had was possibly your key might have been on the hairy edge of being in the full on position. I had an older AUDI and one morning while driving to work, the car just shut shut off and since it was a manual, I simply coasted to my exit as I was close. When I went to restart it, i noticed my heavy key ring had slowly vibrated the ignition key tumbler to the off position. My tumbler was very loose and didn't take much for the key to rotate to a point of no contact. I lightened the load of my key ring and got in the habit of always checking the key to make sure wasn't wiggling to the off position while driving. This may have absolutely nothing to do with your issue but thought I would share just in case you wanted to check the looseness of your ign key tumbler/switch.

 

It's definitely something I will look at. It didn't feel like it was on off, but you never know

 

Maybe not fully off but there is a point between ign off and on and maybe that's where it was. ..or could be the switch itself, the electrical portion I mean behind the physical tumbler.

 

Welp went out this morning to go to work and the XJS just spun over and wouldn’t start. Drrrrrrr! I guess I will be looking into it this week

 

First check for 12 volts at the coil positive. Also, it is a good plan to renew the connector on the coil positive feed, as the copper can break under the connector insulation, giving the appearance of all being well when it isn't.

 

Good thought. I did replace the coil, but it's definitely something else to check. I'm hoping that I'll pop the hood and go "Ah ha!". Highly doubt it, but it would be nice lol 😁

 

Hi Timeisrelative

Just had a thought based on my own experience, as I'm thinking that it could possibly be your CPS Crank Position Sensor, as if it gets out of position or Starts to go on the 'Blink'

It can cut your engine in a heartbeat in just the way you described, which is really handy if you happen to be in the process of overtaking a Truck!

If you've got an AJ6 or an AJ16 Engine replacing it is really a 'Walk in the Park' and can even be done by the side of the road

Though not so much with an XJS V12 ask me how I know or rather don't

 

Yeah that's kinda where I'm leaning towards too, which sucks since I just put a new one on less than a year ago, and have only actually driven the car about 20 times. Drrrrrr

 

To me that sounds like a TPS failure mode- on the AJ16, the car would randomly die this way, and no amount of testing could diagnose the failing part until I replaced in on a hunch- I know you have a AJ6 and your TPS is different, however, but I think this is a more likely candidate

 

Just in case anyone has to replace the Crank Position Sensor on an AJ6 or AJ16 Engine, this is how I did mine but don't attempt it from underneath or you will be there for ever but from on top it only takes a few minutes and in an emergency situation, can be easily done by the side of the road

Providing you have the right socket with a long extension handle and maybe a couple of spanners

How to change the CPS Crank Position Sensor on an AJ6 or AJ16 Engine

 

Ok so I got to look into it a little and I had no spark. I started by checking my coil and I had voltage there. I checked the connector to my cps and looked at the wires up front to see if anything was loose. I didn’t see anything, but tried the switch anyway. Still no start. I then thought “what did I do before I started having problems?”. I realized that I had pulled the ecm connectors and cleaned off the dielectric grease I had put on when I was trying to get it running. I decided to put some dielectric back in and try. I hit the switch and it fired right up! I then went to move the ecm and it shut off. I pulled the connectors again and refitted them and it wouldn’t start! I pushed down on the connectors and it fired right up again! I pushed slightly sideways on the blue connector and it died! Tried starting and nothing. Pushed to the other side and vroom! So apparently my blue connector has some play. I put a piece of foam wrapped in thin cardboard between the connectors and tried pushing and it stayed running! Not a proper fix, but it will work for now!