Hi all -

2008 XJ8 (170K miles) and the motor starts, runs and purrs like it should. No codes of any sort being raised, but I have this odd sound I hear often, similar to a metallic valve chatter. When I drive next to a wall or building, I can really hear it.

But very odd to me that if it truly was some valve chatter, pinging or other valve train situation, I almost certainly would be throwing a code? I use premium gas from the majors (BP, Shell or Exxon). In addition, last night I was driving along a road with a tall wall right next to the car and I heard the sound clearly, more typically when I accelerate a bit. So I stopped, shifted into neutral and accelerated... but no noise. Then I put it into drive and pulled away down the road and noise again. So almost seems to be a noise under transmission load since I do not here it just revving the motor.

I know this is a very vague question, but just tossing it out here for ideas. I believe this car has VVT so could be many issues after 170K miles and all of that complexity.

Thanks - Randy

 

If the VVT stuff is causing problems you will have codes.
The 4.2L engine is very stout and has few problems but with time and age any DOHC engine can have tensioner and/or chain problems.

I would not worry about it and just keep monitoring it in case it gets louder?
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Thanks! Yes... More of a curiosity than a concern ... She has been a great ole girl and deserves to have a few creaks and groans... Just like her ole owner!!

 

ac compressor? they rattle as it wears out

 

Spit balling here.....
Try to repeat your test and select lower gear to see if frequency increases despite road speed being maintained.
That might give a clue as to engine or transmission.

If no frequency change, try going into neutral while still rolling at same speed to see if noise disappears.
If noise still there you might have a bad wheel bearing.
If noise is only under load then perhaps drive shaft centre bearing or a coupling is complaining with some torque applied.

 

I think the sound you are hearing is the engine pinging. My 2008 XJ (118k miles) does the same thing with premium fuel. Under light load, I can occasionally hear pinging when up against a wall/median with the window down.

When you are going up a hill with light throttle you should be able to hear it best. If you go into the throttle more, it should go away. There are many threads about it with no real solution.

My car does not have any codes and has made this noise since I have owned it for 4 years now. I gave up on trying to do anything the car runs perfect should not cause any problems. One user did say replacing his radiator helped reduce it because the engine ran a little cooler with the new radiator.

 

Thanks for more ideas but sound like this might be a "thing" with this car. As I said, more curious than worried.

 

I "think" Snowcone551 might be on to something?
I have noticed the same thing under light load and I think it's the computer trying to optimize the timing for fuel economy? Pushing the timing until you get just a hint of knock and then back off a bit?
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Could just be the fuel injectors. Take a long screwdriver and put the handle to your ear and the tip against the fuel rail. Better yet, buy an inexpensive mechanic's stethoscope which is very handy. You'll probably hear exactly what you are describing, just much louder.

 

Thanks.. not injectors because just idling no noise. Hear while driving and in particular with mild acceleration.

Will keep a listen out for any degradation, but happy she is just still running so well at 170k😁

 

Yeah if its only under load its probably spark knock/pinging (it only happens under load). There are many reports of our cars doing this, probably nothing to worry about if you don't have any codes and its running good. On a nice quite evening take it out and try light throttle to heavy and see how the sound comes and goes? Would be curious if you are having the same sound my car is doing. My car does it under light throttle only. Glad to hear it still running great at 170k, I love my car and I am still catching up to you on mileage

 

My '08 Vanden Plas had made a ping/knock noise for ten years, despite using top grade petrol. The odd time I've had to use "regular" petrol the noise is much more pronounced. I've never had a code and the performance of the engine has never suffered. When it first began I thought it was sticking lifters or valves, but I recall that my '04 and '06 XJ8s did the same thing in their day. I think it is just the sound of the 4.2L V8.

 

So a couple of thoughts to throw in…
1) paying for premium didn’t mean you received premium so maybe throw some octane booster in the tank and give the computer a few miles to sense the difference and listen..?…
2) throw in the tank a STRONG dose of injector & top end cleaner…might be carbon build up causing some pre-detonation
3) while up against the wall and listening..down shift and see if the noise changes rpm’s ?
4) HAVE YOU CHANGED YOUR PLUGS ?
how long has it been? Burned, over sized gap?
5) how old are the coils?…weak under a light load maybe..

 

Could a bad knock sensor be the culprit?

 

Not mentioned if you have had the timing chains, guides, and tensioners replaced with the upgraded ones, but if not?

@ 170K they have been a longish while already in their statistical danger zone as to failure.
Not exactly cheap if done before they fail. But potentially economically fatal to the motor if overly delayed.

Perishable bits in the cooling system come off to do it, so a concurrent refresh of those is neglible extra labour.

Seems that car is worth it. Those among us denied the privilege would love to see it carry-on past the 200K mile goalpost.
Wise to make a plan and see to it. Before it sees to you.

 

I am so glad I found this thread. I have a 2008 XJ8L with approximately 103k miles and mine does exactly what worzella and Snowcone551 described. Engine works fine, no codes, no vibrations, but when driving around the neighborhood and after the engine is warm I'll hear the exact noise when driving up a hill under a slight load and before it shifts down to a lower gear. Need windows down to hear it and definitely between walls or bushes along the side of the road. I thought it could be the sound of a needed valve adjustment job. I guess if it's causing no harm and won't lead to anything worse then I can just chalk it up as a sound an older engine makes. Someone mentioned maybe checking for a loose timing chain, but said that could get expensive fast. Thanks for all of this info on this thread. If anyone ever learns what the noise is and finds out a fix I would be curious to hear about it. Thanks!