Lately I've noticed my car - a 2011 XJL Supersport with 75k miles - loses its customary engine smoothness between about 1000 and 1500 rpm, as though something was out of balance or it wasn't firing on all cylinders. I can feel it through the pedal. At idle and above 1500 it runs smoothly and pulls well. I ran a can of BG44K fuel cleaner through the system but to no avail. Now I'm wondering whether it may be connected to the timing chain tensioner issue that seems to plague this model year - mine haven't been done and they do make the characteristic clicking noise on both sides (I've got the parts, just waiting for my mechanic to free up a lift). Thoughts?

 

Get your guides and tensioners changed before they get so loose that you jump time and trash your engine! IMHO

 

Can you scan for codes?
It's a complicated car and guessing at the problem can get very expensive.
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Here's another twist - I called Gaudin Jaguar, a large local dealer in L.A. and spoke to a service manager. He said that timing chain problems are very very rare in 5.0 liter cars, and he thinks I'm hearing the high pressure fuel pumps. I can't see any reason why he'd discourage business, so what's the real story with these tensioners? To read this or the Range Rover forums you'd think this was a near-universal problem. And that's what the indy mechanics all say as well. It reminds me of the infamous Porsche IMS bearing issue which only affects a small percentage of 2000-2007 cars but every single owner is convinced his car is doomed. Genuinely perplexed.

 

Service Manager at a dealership is mostly dealing with cars under warranty, in this way he is correct - chain issues are very rare while the car is still under warranty. Have a qualified independent mechanic inspect this issue, my local indy claims he can diagnose it by just listening to it run and have done hundreds of chain replacements on JLR cars.

If you don't think 911 IMS issue is serious, you are welcome to buy one in the affected range - without documented IMS fix cars in the range of this issue are very cheap. If you think 5.0 chain is not a problem to worry about, you are welcome to keep driving your car until the chain jumps.

Outside of timing, fuel delivery can cause rough idle at low RPM, usually failing injectors. Coils, spark plugs, fuel pump are all manifest as high-rpm problems, but this is not 100% rule.

 

It could also be something like the engine or transmission mounts need replacing.

 

Another suggestion is to look at some video's about the timing chain problems for your car. Maybe you can see if those noises match what you have?
I do know that DI gas engines are significantly louder (especially at idle) than what I was use to.
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Update to this: I called some more independent Jaguar mechanics and got a range of opinions (and prices, mostly in the $3400-4000 range). Some said this problem is near-universal to these engines (the 2010-4 generation). But another - who I know and trust - said that while the tensioner issue does happen, it's not very common. Much more common in these cars, he said, is that the high pressure fuel pumps pumps make noise, wear out and send metal bits into the injectors which then stick open.

And it is certainly possible that the ticking noise I hear is coming from these pumps, not the chain tensioners. So I've decided to wait and see.

My working hypothesis is this: the original tensioner design was not inherently flawed, but it was not tolerant of owners who stretched out oil changes or used the wrong oil (the sort of customers who take their cars to independent shops only when something breaks). But owners who took their cars to dealers or specialist independents and changed their oil regularly there (and not Jiffy Lube) experience far fewer tensioner problems because they operate their cars within the design parameters. My car's PO took it to the dealer for service, so my sense is that it should be OK. It is taking a risk, of course, but with Jaguars I think you have to accept a certain level of risk or else you can pour money into the car to try to mitigate it - at which point you probably ought to have purchased a Lexus anyway!

 

Sir you are smoking dope Look at my thread https://www.jaguarforums.com/forum/x...t-done-214277/
And by the way my XJ is dealer maintained since day one and oil is changed every 7.5k or six months, which ever came first since new and this xj SuperSport was factory ordered and now has close to 107k miles on it and I am the original owner,

 

Actually no. Please read what Brutal a factory Jaguar mechanic says about this. It is NOT universal and he sees very few problems.
The strange thing is you will see a lot more problems with Range Rovers that use the same engines. But RR sell about 6 to 1 over Jaguars so that could explain it.
I hope he sees this thread and comments on his experience. Using a sample of 1 from individual owners is just about worthless.
Just basic statistics!
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To follow up on this thread, the problem was finally diagnosed and solved: engine mounts.

 

THANK GOD! so much easier to resolve, and lest costly