Hey new to this forum. I have a 2002 xj sport 4.0 v8. just bought it with 138k km on it. noticed what sounds like a knock when letting off the gas. It “knocks” 3 times then sounds fine. Anyone have any idea what I could be in for. Thank you

 

Maybe it's 'Tony Orlando and Dawn'?

 

oh sweet that makes me feel better

 

Perhaps VVT actuation? I never paid attention to when the VVT actually operates.

You could disconnect the actuators at the cam covers and repeat the throttle changes to see if the knock is the same?

It WILL set some DTCs but you can clear them when you reconnect the VVT actuators.(don't do this if you need the readiness monitors for emission check in the near future)

 

Change for 5W30 oil Syntech Castrol... and forget knocks...

 

Thank you all for the input. Any ideas and suggestions are greatly appreciated

 

If the UJ of the driveshaft/prop is worn you’ll have this issue as the tension on the worn bearing is slackened off with de-acceleration. This will cause the play and hence the knocking. I’d advise your mechanic to check it up on the ramp.

 

Definitely not the propshaft as his video is of the car in the garage in park.

Kind of a weird noise to be sure. What about all those warning lights on your dash? I see battery something and you've got the red and amber warning lights on.

 

car currently has a seized alternator so I took the belt off. has battery not charging warning and abs. As to the red and amber warning light not 100% sure. Still have to plug a scanner in and take a look. This video was as I was going to take it to the shop to have the alternator replaced. i reved to about 1500 and let off and it made that “knocking noise” I just purchased the car about 2 weeks ago and this is the first time Iv heard that noise. Oil and coolant look ok from what I can tell also. I’m new to these so I do appreciate all the knowledge and input. Thank you. I’m aware of the tensioner issues with these so that’s the first place my mind went when I heard the noise and I took this video and shut the car off. Haven’t started it since

 

Once you get it back from renewing the alternator, get it warmed up, speed it up, and with a stethoscope (parts stores have them) or a long screw driver in your ear, listen near the throttle body first, then around the engine until you find the source. Impossible to call correctly from an audio, but it sounds like sticking throttle plate . . . try cleaning it and the bore and adjusting the throttle cable.

 

thank you I will