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its undoubtedly your 12 cylinder experience... welcome to the roomier, simpler AJ16 engine, where there’s usually half of anything the 12 has, and it takes 1/4 of the time to replace it!
Hi Vee
You are absolutely right, I keep thinking V12
I know absolutely nothing about the engine on a 4.0L Six
So when I get a Spare moment, I will take some Photos of some of the components that are plugged into the engine and as such would be grateful, if yourself or others could tell me what they do
It does sound like the 'Crank Position Sensor' as has been suggested, so I think I will fit a new one of those and then see what happens
OB
All sympathy to you, and well done for getting the thing off eventually. I cannot answer your question, but on this matter my two questions for the forum about this problem are:
"Does anyone know for sure that the crank sensor controls the fuelling from the injectors, and if the sensor fails the injectors will not open?" and
"Even with a duff crank sensor, the spark will continue to be functioning correctly"
I do not think I have read anyone definitely stating these two propositions are true; but it seems to me they must be if the crank sensor is the cause of your problem, given your symptoms. Bung the new sensor on anyway, and see if it helps, though!
the AJ16 get's it's spark timing from a separate sensor. That sits on the front right side of the engine, on the same auxillary shaft as the power steein pump uses. It is a round distributorlike contraption, which sits where the AJ6 has it's dizzy. So yes, spark will still fly, even if the crank sensor is dead.
The crank sensor is ONLY for the EFI. Like on your V12, the crank is for the EFI. On mine, the rear is EFI, the front is ignition.
Thanks very much Daim. Crank sensor it is then, OB!
Daim, thankfully my V12 is Lucas, so no sensors at either end! Congratulations on that lovely engine restoration by the way.
I have heard one or two people say that these 'Crank Sensors' can lose their Magnetivity over time and so before I ordered a New one, I wanted to take the old one out to see if this were true
Where as you can see from the Photo, the Magnet on that 'Crank Sensor' was strong enough to be able to hold a very heavy Spanner clear of the ground which really Surprised me
So as of yet I haven't ordered a New one, as the Magnet on this CPS seems 100% OK
Where even though I know nothing about these Engines unless someone is able to convince me that I should, I cannot see any good reason for fitting a New one
It wasn't even gummed up with dirt, as the business end looked like brand new
The CPS on the V12 looks very easy to get to in comparison to the 4.0L Six
And while I may not have the mechanical skills of others on this forum, I'm not a 'giver-upper' but this was a job that very nearly broke me!
As without the undertray and the front spoiler removed, this just puts a job like this on another level, to anything that I have ever attempted before
It took all day to get it out and now I'm going to have to put it back
The Magnet on this CPS was Strong enough to hold a heavy Spanner clear of the ground and so if anyone can't convince me that I need to fit a new one I'm putting it back
Mate, the magnetic strength isn't everything. It has to be able to pick up the signals from the flywheel. So the Magnet may be strong right now, but it might not be strong enough to production a useable Signal for the ECU. The Marelli CPS are really wear but are also very close to the crank and the signals are really easy ans clear.
See if you can get a cheap used one prior to a new purchase...
There are pretty much only two things that can get you stranded in the middle of nowhere in your AJ16 or AJ6 powered Jag. Its crank sensor and the basterd hose.
There is no easy way to test CPS, you'd need an oscilloscope to see whether it works or not, plus as any AJ16 or AJ6 owner will tell you, you should keep a spare CPS in the boot at all times. Past the Jaguar hellish bracket that hold it to the engine it can be swapped in minutes and you can continue on your way. TBH it doesn't even need to sit in the bracket.
Last year my CPS failed 250 miles away from my home and I had two spare CPSs, packed in a tool box just behind my house front doors. I simply forgot to take it with me while packing for holidays
Lesson learned, don't repeat my mistakes. I had 4 AJ6 or AJ16 Jags and every single one of them had a replacement CPS sensor at some point, two replaced on the side of the road, one failed 10 meters from home and one 250 miles away from home
After you put the questionable sensor back in, what’s your plan going forward?
No one will be able to definitively diagnose your car from an Internet forum. All we can do is share our experiences.
You have someone here who strongly believes, based on your symptoms and his experience, that this is the part that could be the problem. You convince yourself that everything must be fine with the part because it happens to pick up a socket wrench.
With this kind of troubleshooting, you’re going to have to either invest in some heavy duty diagnostic equipment, in this case an oscilloscope, or use logic and experience to “throw a part at the problem and see what happens”.
I’m really not sure what else you can do. At this point, tow it to a shop and get it diagnosed by a jag specialist.
I've managed to 'suss out' the Bracket, as trying to get that plastic clip open is the 'Job from Hell' where removing the 2 little bolts that hold the Bracket that holds the Plug, only takes a couple of minutes to undo
But how did you change the 'Crank Sensor' by the side of the road?
As I had her Jacked right up in the Air to undo the 'Crank Sensor' bolt from underneath the Car, where absolutely everything is getting in your way of even trying to undo the single bolt, that holds the 'Crank Sensor' in its bracket by the 'Toothed Wheel'
Where I literally had to crawl right underneath the Car, which would seem to be impossible to do by the side of the road and I certainly wasn't joking when I said it took 4 Hours (and may have been longer than that)
So please could you advise me on the best way to do it and apart from everything what I've been doing wrong
I suspect you're trying to get the crank sensor off the bracket itself by removing the little bolt that hold the sensor to its bracket, that might indeed be difficult.
What you want to do is to remove sensor with its bracket and then remove the sensor of it.
There is enough space to get to these bolts from above, to get to bottom bolt use a longer socket or a small extension from under the belt. Remove these two and the whole bracket with the sensor comes out and then you can replace your sensor. They of course might be tight in there, especially when you try to remove it first time. They have been there for 20+ years.
Its more tricky on older AJ6 with hydraulic pump but still doable.
Also two brackets to compare, one is the Andy one, which gives a little extra power and better mpg.
Just to be absolutely clear, I'm not blaming anyone as I know from my own experience that all of us including 'me' are only here to help and Yes! it could still be a 'duff' 'Crank Sensor'
And if turns out that it isn't, then its just one of those things that you just have to accept and then try something else but looking on the bright side which I always try and do
I've learned a lot of new 4 letter words, taken up drinking JD and decided not to end it all so I could live to fight another day!
Which is all good experience like trying to change the Spark Plugs on an XJS V12 which only took me 3 days! (Lol) and Yes! it really did
So please believe me when I say that I am very grateful for all advice received and I'm also very open minded and don't have any fixed ideas as to what may be the problem, as I know nothing about these engines
In which case I have more to lose by not learning anything from the driving experience of an owner like yourself
Though trying to fix someone else's Car from thousands of miles away, is I agree an almost impossible job
But I don't care how hard it is, as if you own an XJS you need to really have a sense of Humour, which doesn't seem to be mentioned in the 'Owners Handbook' for some reason!
And so from this end its all good, so keep that advice coming and one day we will get her up and running!
As I've never done a 'Crank Sensor' on a Six Cylinder XJS before and also the Bracket on my Car (AJ16 Engine) is exactly the same as the one in your first photo (which is a good start)
Working from underneath the Car was with the benefit of hindsight, not the best idea I've ever had and Yes! I did undo that little Bolt, which was yet another bad idea
If I had done it your way and removed that Bracket completely, I'm sure it would have saved me hours of work but I didn't have a clue what I was doing or even undoing for that matter
And enough 4.0L Owners seem to be carrying spare CPS to help to convince me that a failing CPS could be the problem
So my immediate Future Plan is to remove that Bracket that is bolted to the engine like you did, so it will be already for a New 'Crank Sensor'
But did you remove the Top Hose or else leave it as it is?
Never heard of the Andy Bracket, I'll have to look that one up
Yes, that bracket comes off with just the two bolts. I remember doing mine, from the top, without removing anything else. You kinda do it in the blind, by feel and touch.
I think I can do it in less than 10 minutes from unlocking the door to locking the hood. Just eyeball it, so you know what to feel for and then have at it! I forget what size socket you need, I'm assuming 10mm for both bolts.
From a Standing Start with the Bonnet/Hood open, I managed to put the 'Crank Sensor' back in only 60 Seconds instead of Six
Hours!
Then just for fun I did it again, only this time in 30 Seconds!!
Neither which included putting back the plug, which with any luck should be as easy and while I don't want to make excuses, with all the Wiring in the way trying to do it from on top was looking like an almost impossible job
So in the end I decided to do it from underneath, which of course took me a little bit longer
As in about Six Hours Longer!
It was this degree of difficulty that was putting me off buying a New Sensor to put in but now I know how easy it is, I am going to order a New one On-Line right Now (I just put the old one back to have a bit of practice)
And so a Massive Thanks to Both of You for showing me the easy way to do this, although I managed to do it without having to take that main bracket off
Thanks Again
Alex
Last edited by orangeblossom; Aug 22, 2018 at 03:41 PM.
