Brother you are new best friend and hero. I just installed a new rotor and my old girl now purrs like a kitten. I had to order the dist. cap and it should be in tomorrow. I can you, and everyone who replied, enough for all your input. I am sure inputs from this situation will help me later the next time she craps out. I still have no vcm code reading. I will just wait and see how that plays out.
Hope you all have a happy and blessed holiday season.
Gary - if you are worried about your VCM working correctly you can force a condition (non-destructive) that will cause a code to be thrown. Simply remove the connector from the coolant temperature sensor
( see long-time contributor Bryan N.'s post here: [xj40] Code 14 Fuel /Failure - #5 by Bryan_N ) then start your car. You should have a check engine light. Shut the car off, then without reconnecting anything check your VCM and you should see the FF 14 code Bryan describes. Turn the key off, reconnect the sensor, then clear the code, again as Bryan describes in his post. Let us know how you make out.
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Keep a spare rotor in the car
To all XJ40 owners …
ALWAYS keep a spare rotor AND a spare distributor cap in the car.
I’ve owned my car for almost 30 years and it’s only quit on me twice in all that time (seriously). Both times … you guessed it cap or rotor.
Throughout the years we’ve preached the gospel on the forum about this and people still tend to scoff at so simple a fix. So Gary you can now ask, (“Who’s laughing now” 
)
I forgot to mention, there is a modified crank shaft position bracket called “The Andy Bracket” I believe. You can probably find it somewhere on this site. It is made and sold by an engineer in Britain. When you’re changing the crankshaft position sensor it’s simple to also remove the bracket and replace it with the modified bracket. Why? It provides a few degrees of permanent timing advance which gives you more power and better mileage. It’s not a giant improvement but it is noticeable. It would guess 5 more horsepower, give or take? There may be other opinions on here. I think I picked up a couple miles per gallon, again, roughly. On level ground if I were to cruise at 65 miles per hour ( I don’t, ha-ha) I could get close to 25 miles per gallon. It’s fun having the extra power too. Super simple mod. Cheers.
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That’s good, but I believe you have to run high octane gas to suit the mod, right?
At today’s prices I’ll sacrifice the one or two m.p.g to stick with running regular at 20¢/litre less than hi-test. At fill up, that translates into over C$17 a tankful. Thanks very much but using these damn cars as daily drivers costs enough as it is and I seem to have plenty of power anyway …come to think of it, I never even bother with sport mode and still have plenty of get-up-and-go.
I guess if you just drive on sunny weekends on empty highways the bracket may make sense, but for me, almost always dealing with a great deal of city driving, not so much. 
I go to Costco. The spread is only ten cents. I’ve come to the conclusion that the only role for mid-grades is to allow the companies to increase the spread between reg. and premium.
No you don’t have to run high octane IIRC.
The engine has knock retard but it is so very conservative that it can take a few more degrees of advance. It’s here on the forum, made sense when I read it.
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David methinks you are confused. The AJ6 engine has no knock sensor. Perhaps the X300 models or X308 models used an engine with a knock sensor. I once owned a 1997 Chevy Tahoe that had a knock sensor - in the front passenger seat! A/k/a SWMBO.
Ah, the good old days!
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Always makes me laugh when folks insist on putting mid-grade or premium in cars designed for regular, thinking it’s better for the engine.
I guess the logic is if it costs more, it must be better.
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It is the same mindset that the oil companies encourage when they advertise all their alphabet soup additives. They want you to think their gas is super-duper special, to encourage brand loyalty. All oil comes out of the same holes in the ground, refined by the same processes and to the same API standards that car engines are designed to. No oil company can, or would dare to, add some new additive that potentially could ruin 100’s of thousands of engines that aren’t designed for it.
Right, the AJ16 has one and a bracket helps there too; but the AJ6 was mapped in the factory and conservatively so, and it doesn’t have a knock sensor on the engine:
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Thank you for the link. Interesting read.
I had the damper off my ‘92 XJ40 and realised that I could replicate the Andy Bracket by simply repositioning the reluctor wheel on the damper.
Did you actually follow through and reposition it? Did you drill new mounting holes or what?
Yes I did, it went fine never did any full throttle runs as the transmission used to go into limp mode.
I’m not doubting the ‘Andy Bracket’ works, It gets mentioned quite a lot in the XJS section of the JEC mag and I’ve never seen anything negative mentioned about it, but considering the extensive R&D Jaguar put into that engine it does make me wonder how could they miss such a simple mod as that.
They didn’t, they were just being conservative.
My Mercedes has much lower boost than the motor can take and uses more fuel, because it’s the low power option. Every engine you can buy uses a little more fuel and produces a bit less power than ultimately possible. Jaguar just really didn’t want it to knock figuring in fuel quality differences and a few horses don’t matter that much either.
Now we do have more consistent fuel even in the poorer eastern countries and we don’t use the cars to their limit and still expect them not to run perfectly smooth.
Casso, did you read the link posted by David? Its written by ‘Andy’ who supplied the brackets. He describes the reasons as he worked on the engines for Jaguar.
Thanks Robin, I just read the link now ! I didn’t read it first time thinking it would just be a description of how it fits etc. I had a gut instinct there would be a reason for why it was not a standard fitment, thanks for clearing that up.