Hi guys,

Let's see what the brain-trust has for this:

I have a distinct tapping coming from the engine only when it's not loaded. At idle, in Park or Neutral, it's tapping about 200 times a minute. Put it in gear (forward or reverse) and the tapping stops.

Same thing when I driving at a medium speed: If the engine's unloaded I can hear the tapping echo off a curb or wall. However, if add the slightest bit of throttle or take my foot off the gas (negatively loading the engine) the tapping disappears.

I have a stethoscope on order, but it won't be here for a week or two.

Any ideas?

Let the theories begin!

Thanks! - Jim M

 

Idler pulley?

 

my guess...evaporative emission purge valve, its solenoid controlled, and it can get loud over time (mine drove me nuts, just behind the driver side wheel well, and I could hear it ticking from inside the cabin)

 

I had a minor exhaust leak that sounded like that... but it could be a number of different things. You need to be more specific on where the noise is coming from.... top bottom front back, etc...

 

Could be a rattling catalytic converter just beginning to fail. You tend to be able to hear them better at no speed / low speed and echoing off a wall next to a drive-through window....

 

Thanks guys. It's definitely coming from the engine compartment, but I'll remember the purge valve for future reference.

The cat? Hmmm,... that's interesting, because I've been getting P0430 (Left Cat efficiency low) for quite a while now, and its getting more frequent too. And the tapping echo does seem to be louder on the left than on the right. That could be it.

I am hoping it's the idler pulley though. I have to put a new S/C belt on sometime soon. With this many miles on the car (125K) should I just order new idler pulleys as well?

 

Pull the belts and see if the noise persists...

 

The idler does tend to be the first one to get noisy, and its relatively cheap, so i'd recommend a new one while your changing the belts.

 

All good advice. Thanks. I took a look today. There are three idler pulleys - I'd probably replace (or rebuild?) all three.

However, the S/C idler pulley is right up against an electrical connection on the right radiator fan. If I figure out how to disconnect it, will there be room for any kind of normal wrench or breaker bar?

Has anyone ever tried inserting a piece of 1/2" bar stock and then just using a 1/2" open end wrench? (I "assume" it's 1/2"). I really hate the idea of pulling the fan for this.

 

I did my s/c tensioner and idler in my xj w/o removing the radiator. This is the tool that I used.

Serpentine Belt Tool Kit

 

That looks like it should do the job. Thanks Matt. My local Auto Zone has something that it loans out. I'll give that a try and keep the HF kit in mind as a back-up.

Question: Will the car run at all with the supercharger belt disconnected?

BTW: When did you graduate from TT?

Ciao - Jim

 

Sounds like loose torque convertor bolts or a cracked flex plate to me.

 

Take a look at the EGR pipe and gasket as well as the purge valve.

 

I have 2 videos on my link that might help if it is related to the tensioner.

Link JagRepair.com - Jaguar Repair Information Resource

 

While nothing is impossible it's unlikely that placing it into gear would have any effect on a tensioner - chain or belt. Likewise an exhaust leak would probably get louder with the added load. Placing the transmission in gear provides a load against the torque converter which loads its bolts to one side, eliminating the clearance required to 'click'. Same would be true of a cracked flex plate. That's the reasoning behind my response.

 

My exhaust leak was minor. Any time you gave it any acceleration the engine and exhaust noise drowned it out immediately.

 

All good stuff guys. And a very nice discussion. I have a decent set of possible things to check. Won't have a stethoscope for another couple of weeks or so. I'll update things then.

THANKS!