A few weeks ago I noticed that my XJR was making a bit of noise when at partial throttle (maybe 1/3rd?) in the 1800-2200 rpm range - and only really noticeable there. Worse when cold but seems to happen most of the time. I finally got around to doing a windows-down test on my street just to give it a listen, and it sounds much worse than I realized... In the video I put it in 2nd and held down the brake to hold it at part throttle and that rpm range, in normal cruising it doesn't make this noise at all. I know it's asking for magic often if trying to diagnose through cell phone videos, but I figured it was worth a shot. Maybe someone's had similar issues before.

The only thing I can think of is the supercharger, it sounds a little odd at idle, in a way I can't really explain. Almost like the rotors are touching, but not nearly as loud as that would be expected to be. On my next day off I'm hoping to pull the V8 plate and look for rotor damage, I don't really know where else to look after that. Honestly, finding out that this is the blower would be "ideal" more or less, since I have a spare I could rebuild and put in given the motivation.

Link to video: https://drive.google.com/file/d/19fV...ew?usp=sharing

 

Sounds more like timing chain guide failure to me. Better if it's filmed with the hood up, moving the cam front to back.
But after a couple of listens, it still sounds like a timing chain noise.

 

I agree, I have a car here with all kind of S/C noises, but nothing comes even close to the noise in your video.
That really doesn't sound good, I should not be willing to drive it till I knew what it was, try to locate it.

 

Primary and secondary tensioners, chains, guides were all done about 3k miles ago. I guess I could pop a cam cover off, obviously I'd like to avoid having to do that and risking tearing the gaskets or whatever but if the s/c doesn't reveal anything I guess I'll take a look in there

 

You had a problem with you balancer a while back. Did you check to see if that might be the problem again?

 

Just double checked to make sure, the alignment marks that I put on it when I installed the replacement haven't moved so it should be good. That is, unless the pulley is slipping across the rubber isolator in it, which I don't think would cause that noise, and I didn't see any dry rot in the rubber when it was installed.

 

It's also a bit difficult to record with the hood up and moving the camera around the engine, since it happens usually only at speed. Also controlling brakes and gas while keeping it steady around 2k rpm, and not hitting anything, gives enough to focus on aside from the camera... I tried to make it happen while parked, didn't really get anywhere, can't hear much over the SC noise. This was on the same day as the other video.

I know the engine mount should probably be replaced, but it only moved that much once when basically standing on the brake and revving it to just barely before it moves... Testing engine mounts without being that aggressive barely causes any movement usually. Also probably not related to the noise...

I figured for the sake of the transmission I wouldn't do this much more than I already had in this video. In any case, here's the attempt at causing it while parked.

https://drive.google.com/file/d/1ley...ew?usp=sharing

 

You can get a set of chassis ears to help locate the source of the sound while driving. Here is a link to a $100 pair.

https://www.google.com/url?sa=t&sour...-Um0BP_S2iZ91z

 

Can you put white dots of paint on the harmonic balancer including the other crankshaft pulleys as reference to see if your balancer is slipping ?

 

I watched your original video again, is the noise starting upon acceleration in the mentioned rpm range (loading the engine and its parts), or is it always there in that range?

 

Those chassis ears are getting more and more tempting...

I'll paint marker some reference dots on the balancer pulleys tomorrow and see if they're moving over time.

With regards to acceleration, it's not a clear answer... In the video I am holding down the brakes in order to load the engine but keep the car at the same (low) speed and around the RPM range causing symptoms. It took quite a bit of braking, I was getting abs/trac lights on the dash while filming that. In real world driving it does not occur when cruising, but happens anytime I load the engine with more than just cruising (gentle acceleration, going up a steep hill, and so on) but only in that RPM range, and it seems that it's only at part throttle, I don't notice it at full throttle. That being said, there's more normal engine noises at full throttle, and when you're at wide open on these cars, it won't stick around at 2k RPM for long.

 

My first impression upon seeing your initial video was something mechanical.
A belt driven fan starting to touch it housing or alike.
But as our cars don't have those, forget about it.

As also suggested, I can imagine one of the primary belts slapping around, worse at certain rpm's due to induced frequencies.
On the other hand, if you have done your job well, you are the one knowing the best if this one can be ruled out.

That almost leaves something mechanical excluded, and time to think about other causes.
Although a long shot, can it be something vacuum related?
Can it be vacuum noise?

Some of us (Harvest 14, me, some others) have or had an almost mechanical grinding from the middle of the underside of the intake manifold, following the partial-load hose backwards (partial load? sounds related?).
But only for a split second, and only if you blip the throttle.
I never read about anyone finding the exact cause, or solution.

It is the same kind of noise as in your first video, only less pronounced, and again, I only hear it if I blip the throttle while standing at the engine bay.
Maybe you can have a check on that?

 

I cracked the V8 plate open today to inspect the supercharger. No dice, it was very clean, no scratches apart from a couple very minor chips in the coating. About halfway through reassembly I realized I could have just undone the SC belt and test drove again, to isolate the SC as a cause. It still happens without the SC connected. I tried to get the noise to happen again while parked, with the SC undone, but without it the engine doesn't have the power to overcome the torque converter up to where the noise starts. Guess the cam covers come off next.

For the throttle blip noise, does it happen immediately after bumping the throttle, as it is picking up revs? I'm not sure if I've noticed it before, but there's a lot of noises I've gotten used to as normal engine sounds so far.

 

With the serpentine belt removed and your observations as I understand it ( unless the S/C engine has 2 belts ) eliminates the possibility of of belt tensioner and idler pulley

 

It actually happens during the 'blip', but only if you blip it fast.
I have no idea at what rpm's, but I guess a 1500-2000 is an estimate, I am not a madman rev-ing the engine unloaded.

The only way I mentioned this, is as your noise comes closest to this of anything I have heard on my engine, and it kind of si the same rasping noise (although phones and computer speakers might distort it from reality.

I can see tomorrow if I can make the noise longer (maybe it is long gone), but I think I tried this before when we ere trying to solve this mystery with Harvest14.

 

@Lady Penelope - the SC engines have 2 belts.

OK having listened to the 2nd video, it sounds totally different to the 1st!

I now think it's more likely accessory related. But that means a number of items to check. Firstly belts and bearings, then onto the air-con pump, pas pump, etc. I now doubt the timing chain system...going by the 2nd video.

 

Right after I bought my X300 I had a similar noise. Put it on a rack and sounded like it was coming from the bell housing on transmission. Took it to a tran shop to have it serviced. They found it to be a loose alternator. Oh, well.

 

I had something similar earlier in the year. Checked all over , almost took the timing chain cover off just to check that my handy work was still ok from when I did the timing chains. The noise seemed to come from the top end so was thinking con rod bearing, cam bearings, tappet clearances etc.,Turned out to be cat rattle, only made the sound on deceleration and in the 2000-1500 rpm band. Changed them out and it went away, on removal, just giving the cat a shake and you could feel the internal honey comb moving around. They must resonate in the 1500-2000 band

 

Pulled the accessory belt and spun/jiggled everything, all seems to be in order except that the PAS pump makes a bad ticking noise when spun quickly by hand. I already kind of knew about that though, I've got a hopefully-good replacement pump waiting to be installed once I get to it. Belts and idler bearings were all done recently, and the alt was also replaced recently. Double checked those just to be sure as well.

If it's affected by throttle position, then it shouldn't be accessories right? If the engine is spinning at a speed, the accessories are spinning at that speed, regardless if the engine is putting 15hp or 200hp to the rear wheels. If it was occurring during a change in RPM then maybe, but even if held at constant RPM the noise still happens. I guess I could test the noise with the acc belt undone, but I'd be worried to run the engine for more than several seconds with the water pump undone.

I ordered up those chassis ears, will see what that comes up with when they come in.

The cats is an interesting idea, I'll be sure to check on that when I get the time and the car's cold.

 

I had a similar knock this summer and found that one of my somewhat new (10k mile) 2ndary tensioner neoprene guides had come off (left bank). The chain was slapping on the end of the tensioner by the time I got to it. I think it slowly broke apart as the noise got worse and more consistent. I had another set, so I just replaced it, but it sounded very similar and was very prominent when cold and the noise wasn't consistent. I to thought it was a supercharger issue, I found it using a simple motor stethoscope. Once replaced I pulled the oil pan and removed all the pieces, including in the oil pickup.