So I've got an intermittent knock that comes from the engine, mostly once it's warmed up and idling. I've taken a video of it and posted it below - this is how it sounds from the interior. I'm taking it to the dealer today because I'm also getting an awful engine vibration in the 2,000-2250 rpm range, regardless of whether I'm in gear or neutral. Does this sound like the harmonic balancer? Or do you think it may be something directly wrong with the crankshaft? Doesn't seem like it would be an engine mount at this point.

I want to make sure my tech is thorough, because if it is the balancer, I'm sure all of those torsional forces have been going directly to the crank and the transmission. Here's to hoping he can find exactly what is going on! I've just crested 65,000 miles as well.

https://www.youtube.com/watch?v=njh1...ature=youtu.be

 

I listened to your video and didn't hear any knocking noise, even after turning up the volume on my PC and replaying it several times. All I heard was the exhaust throb.

Here's a good primer on engine noises: https://www.bellperformance.com/blog...-engine-noises

Since you're taking the car to the dealer today, don't tell them what you think is making the noise and vibration. They're the experts and let them evaluate it. Just make sure that your dealer's technician uses a stethoscope to pinpoint the source of that noise before taking anything apart.

 

Is there vibrations felt through the steering wheel? My bet is you need motor mounts.

 

You can feel the vibration through the whole car - steering wheel, pedals, seat - even passengers can feel it. Highway speed puts it right in the sweet spot for the vibration, but if I downshift to 5th (higher rpm) it goes away.

 

If you look at the air intake bellowed sections. The pleats should be evenly spaced. If the bellows are pinched at the top then your motor mounts have collapsed by losing the hydraulic fluid and, therefore, the vibration you feel. I recommend replacing the 2 motor mounts and the transmission mount and life will be sweet again.

 

XJsss, the dealer called today and said in their voicemail that they diagnosed the problem as being a faulty fuel pump. Not sure how that would translate into an RPM specific vibration, but hey, they're the experts, not me! I'm going to have them check the supercharger isolator as well. I'm thinking maybe that intermittent knock is related to TSB JTB00349v2 instead of the timing components.

 

Be advised there are 3 fuel pumps on the XJs. One is in the fuel tank to send fuel to the engine pumps that are mechanically driven by a small 2 lobe "cam shaft" that supply fuel at high pressure to the direct injection injectors. As for the supercharger pully isolator I've had that replaced as my tech found play in the pully when they where replacing the coolant pipe betreen the heads.