Hello all, ever since I've had my 01 XJR it's made this ticking/clacking sound when started for the first time if it's been sitting a day or two, and it hasn't get worse or better over the 3k miles I've owned the car. The funny thing is that it only makes the noise when cold, also when you put it in gear the noise gets much louder as seen in the first video. And as soon as it has warmed up for the day it will no longer make the clicking/knocking noise; however, if you are in a quiet area like my garage, I can faintly hear the "blowing" sound of an exhaust leak when warm after a drive. The engine has 73k miles on it, and I have done the timing chain tensioners the engine looks immaculate inside, with absolutely no sludge. I have tried ZDDP oil additives and injector cleaner in the tank, and I have listened all over the engine with a stethoscope and am unable to pin down the source of the noise. the closest I have come is heard in the second video, where, again the audio isn't super representative of the noise in person. in that video and in real life there is a clear "blowing" and "clacking" sound coming from the passenger side exhaust manifold area. FYI the cold start video doesn't represent the sound well, it makes it sound much louder than it really is. When I change my oil next I am going to send an oil sample off to Blackstone Labs to get analyzed to make sure the engine isn't eating itself, But in the meantime, the noise is bugging me, and i'd like to get to the bottom of it. apologies for the long videos I didn't have any help filming.

OVERVIEW:
- Makes noise when cold
- Worse in gear
- 99% gone once warm
- noise also disappears above 1k RPM even when cold
- No engine codes stored or pending


VIDEO #1: https://photos.app.goo.gl/94whbqL2kurHMbdq7
VIDEO #2: https://photos.app.goo.gl/e4UkxijtCczGVAZq8

 

To me it sounds as a piston slap. Piston slap only occurs when engine is cold and gets worse under load. Load here is gearbox and brakes. If there is blowing from the either side manifold it can be cracked manifold or just seal bad.

 

Maybe, I had considered that, but it seems pretty unlikely, considering the mileage and condition of the inside of the motor. But I do agree that it does sound like it.

Edit: any other opinions are welcome. In the mean time, if it is a piston slap, I think I'm going to try to unplug each injector one at a time to see if I can pinpoint which cylinder it is.

 

My 01 XJR does this too. Piston slap noise for the first couple of minutes, then nothing until the next fully cold start. I remember another thread a few months ago, a member was able to stethescope it down to one cylinder by listening to each coil, swapped that coil with another and found the sound moved, new coil fixed his noise. I haven't done this yet to my car, but its on my list...interested in what you find as well.

 

Huh, that is strange that the sound moved! Maybe a failing coil is causing some uneven ignition which causes an otherwise in-spec piston and bore to "slap"? I'll update this thread when I know more. Could you link that thread if you remember it? id love to give it a read!

 

Small update, I have since solved the exhaust leak heard in video 2. turns out that when I did the secondary tensioners, I took the spark plugs out to inspect and apparently, I didn't tighten 2 of the spark plugs on the passenger side. Stupid, I know! they were finger-tight and leaking a bit which could be heard the second the coil cover was taken off while running. Strangely this didn't cause any misfires or codes. as for the other "piston slap" sound, the car was not dead cold, so I couldn't test for it. But I have left the coil covers off, and tomorrow I'll give it a test and see if I can pinpoint the sound.