I was driving the XJS 4.0 a few weeks ago and it appeared to cut out on the highway (just like the key was turned off) for about 1-2 seconds. I noticed the rev counter drop to zero and then everything returned to normal. No warning, no splutter, no nothing. The Check Engine light came on and I nursed the car home but there were no other issues. Unfortunately I did not get the error code but I drove several short'ish distances over the next few days trying to repeat the problem but it did not reappear and it happened so fast I started to doubt myself so I reset the Check Engine light. No more issues until yesterday. Driving home on the Interstate, doing around 65-70, not accelerating hard just cruising and it happened again. Engine shut off, rev counter to zero, all lights on dash, car was coasting just like I had shut off the key. No issues with steering or brakes. I coasted for about 10 seconds slowly beginning to move over to the right to pull off when everything restarted without me doing anything. The Check Engine light came on but the car was running fine. I cruised for another approx. 10 careful miles then, about a mile from home, it did it again. This time it did not restart by itself. As the car slowed I put it in neutral and coasted to a safe spot. Once stationary I put the car in park and immediately restarted it using the key as though nothing had happened (although the Check Engine light was still on). When I checked the Error Code it is FF69 which is I suspect because I went from Drive to Neutral while it was moving and coasted to a stop. I did not put the car in neutral when it happened earlier that same day when it restarted by itself. There are no other error codes reported.

Any suggestions or has anyone else experienced anything similar. Car is mint with just over 30,000 miles. Full service history, everything works fine until this. I suspect something electrical based on the symptoms, not fuel, as there was no splutter or warning signs. The FF69 error may be valid, I'm not sure. Appreciate any advice before I go off down a rabbit hole. Thanks.

 

Have you downloaded the S91_AJ6 4.0 Engine Management.pdf?

14mb file size and you can find it on the internet.

 

WOW, that document is excellent. It doesn't appear to tell me what might be the root cause of my issue. It does go into great detail on FF69 and others so it's very useful flow for troubleshooting. Would the Drive/Neutral input circuit cause the engine to shut down and apparently all electrics to cease?

 

Hi Brit1965

Assuming you've got the AJ16 Engine in your Car

My first thoughts on this would be 'The Crank Position Sensor' that can suddenly go very flaky for almost no reason at all and that is why many drivers of the XJS 4.0L (6 cylinder) 'including myself' tend to carry a Spare one of these in the 'Glove Box'

As a Faulty Crank Position Sensor can simply cut your engine dead, in the way you have described just as if you had gone and turned the Ignition off

Where the reason that I know this is because it happened to me and so could easily cause you a Fatal Accident, in the event you were overtaking a Truck or anything at all for that matter

So while you've seem to have got away with it so far

Next time you may not be so Lucky and so I wouldn't be 'Rolling The Dice' if I were you

On the face of it having to change the Crank Position Sensor is a 'Nightmare of Epic Proportions' as the first time I did this, I tackled this job from under the Car and it took me nearly all day and was such a PIA to do that I was literally one away from booking in for Therapy and Counselling!

Though once you know the right way, then you can literally do it by the Side of the Road in a Couple of minutes

(if you've got the right size Spanner with you!)

So instead of going from underneath like I did the first time, tackle the Job from under the Bonnet/Hood from on Top

No real need to disconnect any Hoses although maybe just a little trifle easier if you do, especially the first time so you can see how it all hangs together

There is basically just one Bolt to undo and a Wire to unplug, which is a whole lot easier if you undo the other Bolt that holds the Bracket that holds those Wires in Place (needles to say don't drop that Bolt down on the Ground or you will surely lose it and also don't lose the Big Special Washer behind it

So far so good but now we come to where the 'Magic Happens' especially when it comes to putting it back, as you can't see what you're doing as you hand will be right in the way

Where in order to overcome this, you have to look and take a Snap Shot in your Mind, where once having done so you do the Job by Memory and the Feel of what goes where and then you Start her up and off you go

Maybe the Gap just needs a bit of Adjusting of else maybe the Sensor is Covered in Crud and needs a Clean

Or maybe it is none of those things and you just need to get yourself a New Water Temperature Sensor, that can be checked in various ways including Bridging the Terminals with a Piece of Wire or 'Paper Clip' aka 'The Paper Clip Trick'

If none of that Works then there are lots of other things to try

Although I think the Crank Position Sensor, would probably be the First thing I would gravitate towards

This is how to do it: How to Change the Crank Position Sensor: How to Change the Crank Position Sensor XJS 4.0L with AJ16 Engine

 

Here are the three items that are most likely to cause your problem:

1. Camshaft position sensor- not expensive, should take 15 minutes

2. EGR Valve - more expensive, perhaps cleaning is possible, but I’ve never been able to get positive results.

3. TPS - very expensive, simple to replace. You may have the kind that collects fluids and can be drained. Check forum posts. AJ16 TPS cannot be serviced, I believe the AJ6 can.

I’d do it in that order, only because of the costs involved.

 

Thanks to everyone for the helpful responses. Great forum!

 

And yes, it is the AJ16 4.0L engine

 

The 1994MY 4.0 liter engine is OBDI and is the AJ6 engine. (NOT AJ16)

 

Brit1965

I guess it depends if you're referring to a car built in 1994 or a US 1994 MY car.

I have a 1994 AJ16 car (1994.75 MY) If your VIN is after 194774 then you will have an AJ16 engine

I can't add much further to the other thoughts as to why the car might cut out. Although an erratic ignition switch might also cause it. But if the engine isn't running then you definitely didn't have any power steering. And your power brakes wouldn't be operating properly either.

The really intriguing thing is how the engine started itself after cutting out! I can't work that one out at all!

Good luck with the problem

Paul