Hi all -
I am in the midst of cross-country drive number four, and reading about timing chain issues, and I'm nervous. Here are my symptoms:

First: the car runs fine. For now.
But: I've been hearing something funky, and it's been getting worse.
I ALWAYS hear it (and ONLY hear it) on acceleration. Once I'm at speed, even at 90, no noise.
It's definitely an engine noise.
If, say, I'm pushing it hard on a freeway onramp, I hear this ticky-tack, light knocking sound. Like a faint, rapid ticka-ticka-ticka-ticka.
Best description: it sounds like what was, back in the day, pre-knocking from bad gas. Not a low, bearking knock, but a higher, lighter, tap-knock.
As I said, once I take my foot off the gas it goes away.

It was suggested that this is injectors but I can't see how this makes sense.

Like I said, the car fires right up, so I can't say there's a problem, BUT-- as it's been getting steadily more noticeable over the past months, I'm nervous. (And I tried to record it but between engine and cabin nose it's impossible.) Any insights would be much appreciated.

 

I congratulate you on using your car for what it was built for, high speed touring. But, I think that you should have that noise looked into right away. Noises like that aren't normal. If you can prevent a major failure you'll be dollars ahead. Good luck.

 

A sort of high-pitched rattle? Do you only hear it on hard acceleration? By that I mean, hard acceleration. When you bury your foot into the carpet, maybe in sport mode? If you accelerate purposefully, but more gently, do you still hear it?

I ask because I get something similar. Only under hard acceleration, goes away if you ease off the gas, never under 'normal but spirited' acceleration, never when under light load (not accelerating) regardless of speed. Only when I mash the throttle.

My car has done this for a long time. I have reported it to the garage and they can find nothing untoward. The car is running perfectly - just completed a 2,000 mile road trip to the South of France (from UK) without missing a beat. Never once heard the noise on that trip as I never once gave it maximum beans.

If you find out what is causing it, or anyone has any ideas, I'd be most interested. I am fairly sure, from your description, we are talking about the same thing.

One point - mine is the 4.2 supercharged, 2008 model, not the 5.0. Which is yours?

 

Are you sure it's not the supercharger torsional isolator? Has your car had a replacement in it's lifetime?

 

Not my car. Or, more accurately, not recorded in its history (which is complete as far as I am aware).

To aid my general understanding, could you elaborate a little on the supercharger torsional isolator, with regard to the 4.2 models? Or maybe point me to info elsewhere? Thanks.

 

https://www.jaguarforums.com/forum/x...olator-137560/

 

Barnsie: I've noticed it on "spirited" accretion for a while. Kind of like what you describe.
I'm concerned because lately it's also on "medium" accretion, so whatever it is, is becoming more pronounced.
Still OK on "gently from a stop" acceleration.
Yep I've got the supercharged 5.0.

Jagrag: I had the supercharger rebuilt.. The symptom then also sounded like bad gas: about two seconds of knocking after engine shut-off. So they rebuilt the whole thing. Problem gone. This seems different, and no post-shut-off knock.

 

Has the car thrown any codes?

 

I've the same symptoms which only manifest at 4k rpm, I don't normally drive in thst range and it was first spotted when I had the car dyno'd earlier in the year, in my case it's the isolator coupler

Attached is the price list of the bits bought. But I'd suggest you first take it to a decent Indy to diagnose. A rattling coupler won't throw any codes...or at least mine didn't. In my case good news as today got warranty company to agree to pay the costs....after much persuading with their MD

 

Tickity tickity under load like an exhaust leak and scratching at idle is the SC coupler on the M112 equipped engines. Don’t know why it’d be any different on the TVS.

If it’s a chain guide issue it’ll probably give you some warnings at idle and start to rattle all the time.

 

Xalty and Barnsie,
Not to highjack this thread, but please elaborate on the 4.2L SC torsional coupler issue (I have an '07 4.2L with Eaton M112, currently apart awaiting valley hose parts delivery)
- Belt off, how much (if any) rotary free play is allowable at SC pulley? (i have only about 0.030" TIR, which I assumed was just SC gear backlash. No info I could find in Jag manual)
- With hood up, idling, and engine cover off, I did hear what sounded a bit like an intermittent lifter tap
- Reading Post #6 link (thank you for this, Jagrag), not sure if this might be coupler, or "rotor knock??", or totally unrelated (yes, should have run engine with SC belt off to see, but didn't...)
- Would pulling snout off SC (while its on the bench) and replacing (spring type OE) coupler with an aftermarket plastic one be a good idea, even with only 0.030" rotational free play?

(Lots of 5.0L SC info in this thread. Hope this post might help us 4.2L SC types, particularly as the miles and years accumulate...)

 

I'd love to help, and would love to have the answers you seek, but I am a technical ignoramus I am afraid. I very much admire the people here would do their own servicing and so on, but I don't have any of those skills at all when it comes to mechanicals. So I am as interested as you are in the issue you mention. I wouldn't be able to even contemplate fixing it myself, but it's always good to read about these things so that I can give a more informed brief to the Indie garage which looks after my car (very well).

 

No idea on play or other specs. This the noise it makes at idle and at speed it becomes a rickety tickety. If a coupler doesn’t resolve it it’s usually rotor wear and in which case just live with it.

 

Thanks all
(Appreciate the video clip Xalty)
- Also noticed that - with one hand holding the rotors stationary, the SC pulley can be moved easily ~30 degrees against the coupler spring (with other hand). Seem weak?
- I'll call a supercharger specialist on monday and get some advice; will post resolution here