Hello all, I'm back with more starting issues. Sooner than I would have hoped. Some of you may remember my no-starting woes from last month, old thread linked here: https://www.jaguarforums.com/forum/xj-xj6-xjr6-x300-26/not-starting-cranking-spluttering-but-wont-hold-idle-276895/?ispreloading=1

This thread hopefully won't be as long as my previous one, but you never know. Well, the Jag has been running faultlessly for two and a half weeks since I swapped the ECU. I parked it up on Tuesday night after about two hours of normal driving spread across the day, then on Wednesday morning it would not start. The car turned over but would not fire. I tried jumping it off another car, still no luck. I had to get to work, so I left it at that. After work, Wednesday evening, the car fired right up with no questions asked. I let it idle for a minute or so, then turned it off.

This morning, it fired up again, and I drove it round to a different spot on my drive with no issues. Left it to idle for a few minutes, then turned it off. This evening after work it did not start again. After a few tries it spluttered into life and idled for two or three minutes, then gradually got worse and worse, idling with more roughness until it died. I noticed after that that there was no movement of the tachometer, so I immediately suspected the CKPS. I removed the CKPS (which I only replaced in January as part of my last battle with this car) and gave it a thorough clean, along with the car-side connector. Re-attached everything, and had some life in the dial again. When cranking, the tach bounced between 0 and 200 quite a lot, and the car sputtered a few times before finally firing.

This time it idled for another 5 minutes or so, then died. Attempts to restart it after that ranged from no start with no movement on the tach, to rough starts, normal idles, then gradual stalls. While idling, any stab at the throttle would make it stumble and shake the whole car, with occasional backfiring. Then it inevitably dies. This is all done on a cold engine, with one week old fuel. I checked the filler compartment drain was clear and draining properly, so I think I can rule out bad fuel.

My suspicion is with the CKPS, but would a failing CKPS cause the car to run rough then die altogether? Would it cause the stumbling when throttle inputs were given, to the point of stalling out and backfiring?

More Jag fiddling in store for me, it seems.

 

The CKPS defiantly enables the fuel pump and your tach jumping and rough running

But there are some free things you can try first

Relay swapping

Right engine bay fuse box , large ECU Control relay # 5 right , right heelboard fuse box

Swapping relay to put in , left engine bay fuse box and Headlight , A/ C Clutch , or fog light





Editing

 

Thanks Parker, I'll have a go at the relay swapping over the weekend. The CKPS I bought new in January was only a £16 one off eBay, so it might have just been a poor quality item that's failed after only a few hundred miles.

 

The general rule has seemed to be that there is never any rhyme or reason to symptoms of CKPS problems, and I remember a thread in the past where it was suggested , tongue in cheek, that the first sentence in the service manual should read “open bonnet and replace CKPS” . Well worth trying a new sensor.

 

Morning all, I haven’t had time to try anything more on the Jag over the weekend but I have started it a few times. It’s started and idled ok now, which is annoying because I can’t replicate the issue I had despite nothing changing. It even revved up freely without stumbling or misfiring.

One time on a mildly damp evening, it squealed loudly continuously after starting from the alternator belt, even after several minutes of idling. I suspected this would arise at some point due to the following symptoms:

1. Occasional squeal on startup.
2. Lights dimming when using electricity, for instance operating the electric windows.
3. Voltage dropping to the point of battery warning light coming on after driving through a puddle. The belt squeaks, dries, voltage recovers.
4. On the last drive a week ago before it started playing up again, I noticed under hard acceleration at high revs the lights would dim also, suggesting the belt was slipping when rotating rapidly.

Would a slipping belt cause any of the issues I’ve had? And how do I go about tightening/changing the belt? Thanks.

 

Evening everyone, I have tightened the alternator belt by adjusting the two 15mm bolts on the tensioner arm, and the car started without squealing. The lights don't dim as much as they used to when using other electrical systems, and at full throttle and high RPMs they didn't dip at all either.

The car got up to temperature smoothly, without misfiring or stumbling. There was the occasional drop in RPMs when stationary and in gear, but only from 900 down to 800 ish, then immediately back to 900.

This seems to have solved the issue. It may have even got rid of the grinding noise on startup, but I can't be too sure of that. The CKPS may still be failing but since cleaning its connector the tachometer has been fine every time, I'll order another to keep in the boot just in case. I've never known a loose alternator belt to cause these kinds of issues, luckily it was an easy fix.

If there aren't any more replies from me, consider this starting issue solved. If it breaks again I'll be back with an update. Ciao!

 

As the alternator has been replaced with the wrong size belt before as there is little adjustment.

The size is 395 cm ( off my head ) from my belt marked as a official Jaguar stamped part

The grinding noise may be a original timing chain tensioner until oil pressure comes up

The revised tensioner will have a stamped arrow on the body

No big deal as I have never heard of one timing chain breaking , built like a tank

03-1-09 Rattle After Start.pdf (jagrepair.com)