Hi!

I`m new to this forum...... From about 3-4 month I have a big problem with 2003 XJR supercharged. The engine develops loud metallic knock under wide throttle acceleration above 4000 rpm. Also when on neutreal you rev the engine up to 4600rpm it also develops this knock but only when you depress fully throttle pedal. Tonight I`ve removed supercharger drive belt, started it up, revved and it stopped knocking, I`ve drove it in this condition and there was no knock. When I installed supercharger drive belt back on the knocking comes back. I`ve tried several chargers, i bought a new one..... knocking still there...... I`ve also replaced:

1.All coil packs
2.All spark plugs
3.New Supercharger
4.All timing chains, tensioners, guides
5.All idlers, pulleys, belts on the engine
6.

 

I went to the doctor with a sharp pain in the lower abdomen that occurred only when I tried to pick up a heavy object.

Doc said "don't pick up a heavy object".

Assuming that all your work has been done correctly, you have eliminated all the potential issues except the engine short block.

 

it only knocks when the supercharger is belted? hmmm...

 

I don't know how the supercharger is driven on this engine, but it sounds like a crank driven belt? If so, check for a crank pulley failure. If the elastic bond comes apart on such a pulley it can cause some strange symptoms.

 

Never mind my pulley failure post, I just re-read your parts summary.
Wow man, not good.

 

Today I drove it......

And now this rattling, pinging sound comes on later.... I mean at about 5000 rpm..... and is much quieter......

I just don`t understand why it changes so much.......

I`ve reread trouble codes..... and got no codes, no check engine light.... the engine pulls hard

 

Two observations:
First, you say, "Also when on neutreal you rev the engine up to 4600rpm it also develops this knock but only when you depress fully throttle pedal." While in my humble opinion, this is not a very good thing to try anyway, I was pretty sure the XJR had a rev limiter in nuetral or park that limited engine revs to 30000 rpm. So, I wonder what part of that does not add up.
Second, your symptoms changing from knock to ping is somewhat encouraging in that it MIGHT not be the engine lower end coming apart. It MIGHT be a lean condition or a problem with the knock sensor. I assume you are using good high octane fuel, right?
Good luck, and keep us posted.

 

Generally i see that this problem is related to position of throttle valve....
On neutreal you can get the engine to rev up to 4600 rpm with 70% of depressed accelerator pedal....... the engine hits rev limiter and there is no knocking.... but when you depress accelerator all the way the revs don`t change but knocking starts......

I`m running 98 octane
I`m not running lean

How to check knock sensors......? I have no faults, codes, ect.

 

My engine started knocking due to lack of oil. I changed the oil it is even louder now. tap tap tap noise increases with higher RPM s and gets silent at high speed..
any idea?

 

Yes, I have two ideas... 1) you should not run itr out of oil ) Now you will pay the price. You MIGHT save the engine with just new bearings, bit your engine is most likely toast.

 

Nikos - any resolution?

You could well be running lean and when the SC is running the effective compression is much higher, so pre-detonation or pre-ignition may be what you're hearing. With the SC disconnected, the cylinder pressure goes down, lean induced pre-det/pre-ig goes away... a plausible scenario, but how to verify?

 

colour of plugs, light brown is a dead giveaway to pre-det.