So, I've had a slight noise on acceleration for a while now and wasn't sure if it was "normal" for a Jaguar engine or something that needed correcting. Over time a very slight irregular engine noise has developed at idle, but not a sound anyone but myself would notice.

Today I isolated the sound to a particular cylinder. I used to know how they are numbered but I don't remember, so it's the second one from the firewall on the passenger (RH) side. I pushed the throttle body to about 2,500 RPM with my ears near the engine and it is definite, that cylinder gives a pronounced rattle at that RPM. I feel certain that's my noise.

Is this a failing coil? Is this a failing/loose spark plug? Is this a valve problem? Is there a worse case scenario I should be afraid of? The car is still hot so I probably won't take anything apart until tomorrow.

No engine codes. Fuel trims are quite good. Car drives well, smooth and powerful.

Any gut reactions?

 

I might have the same thing, but located it more 'under' the intake manifold.
Should say the sound is more like rasping then a rattle.
Sounds familiar?

I got one suggestion from the forum, being the EGR valve.
I did not dig into this deeper yet.
https://www.jaguarforums.com/forum/x...1/#post1373810

 

I didn't think the normally aspirated XJ8 had an EGR system. I thought that was only on the supercharged models. Maybe I have been wrong, I will research that. Thanks.

 

I decided to check a few things tonight after the car cooled down a bit. I pulled out the coils on the RH bank and took out the two middle spark plugs (cylinders 2 and 3, if I'm not mistaken). There was no oil leaking anywhere and the plugs looked healthy. I used a camera with a flexible tube (automotive inspection camera) to look inside the spark plug holes. There seemed to be a little more build-up on the #3 piston than the #2. Not sure if that means anything.

I switched those two plugs but put all the coils back in their original places. Car started right up and ran fine, just like before. The noise comes back at higher RPM but using the stethoscope it seems I was mistaken about the sound coming from the #3 cylinder. It actually does seem to be coming from the manifold/throttle body area. And yes Eric, it could more accurately be described as a rasping sound rather than a rattling sound.

 

Look at this thread, and the YouTube link post 1.

https://www.jaguarforums.com/forum/x...ft-vvt-120991/

https://www.youtube.com/watch?v=5eEV...ature=youtu.be

Eric

 

My 98 XJR has NO EGR valve.


The JTIS states in its instructions to change the EGR valve " remove engine cover "


The supercharged engines do not have an engine cover.


I would have a look for an EGR valve if it were my car, and if it has , check the pipes for splits.

 

I did a bit more internet checking, and it seems u are right, no EGT valve on the NA XJ8, only on the SC's.
Seems very little left under that manifold which can cause the rasping .. (Ignore the arrow, pic is from a coolant thread).

 

What are the fuel trims? If a lot more than +4.7, You might have a manifold leak (need a new gasket).

 

The short term fuel trims do occasionally hover around + 9 or +10 at low rpm. The long term stay around +2 on bank 1 and +5 on bank 2. They both frequently go lower, though.

The manifold gaskets were replaced a few months before I bought the car. Since they put the coolant lines back on wrong I guess it is also possible they botched the intake gasket installation.

I ordered a smoke test machine; it arrives Wednesday or Thursday.

 

I don't want to interfere too much with the OP's post, but I will follow this thread as we look to have the same noise.

Some additional info which might be helpful:
My fuel trims are perfect (LTFT within 3%, and often close to zero), and well balanced (less then .5 between them, often same for both banks).

I had the coolant hoses replaced some 2 years ago, and the indy installed the manifold with new gaskets.
Considering the trims, I doubt I have a leak there.

Last thought; I just had the intake manifold off from our SLK to replace a broken bracket.
MB's manifold is full of plastic valves, opening and closing at different RPM conditions, to shorten or lengthen the intake trajectory of the air.
I presume the Jaguar intake is much simpler, but is there anything inside the manifold which can leak or swirl air?

E.

 

This thread was started regarding a "cylinder noise", and has certainly gone down a couple of rabbit holes since then, lol.

I did the brakes today; Akebono Euro pads and Centric premium rotors all around. Everything came off easy except for the front caliper brackets; those bolts were tight!!!

I used my power bleeder to flush out all the old brake fluid, but the fluid that was in there looked pretty good. Since I couldn't really tell when all the old was flushed out, I just let the rear ones flush for about 4 minutes each and the fronts for about 1 minute each, with about 15 lbs of pressure pushing the fluid. I drained out about 3 pints so I'm hoping that's enough to consider it "flushed".

Questions: This sounds dumb, but how do I tell if the brake fluid reservoir is at the right level? It's about 5 mm from the cap now, is that too much? I don't see a "full line".

The smoke test device came today. I am very anxious to hook it up and see if there are any vacuum leaks. Since I spent the better part of the day installing the brakes and have had precious little time NOT working lately, we are going to have family game night with the kids. So, that means I have t wait. But first thing tomorrow though I will be testing that new smoke machine out.

Where is the most logical place to hook into the vacuum system to introduce the smoke?

 

Ok, I'm going to start a new thread with this next question, but I wanted to report to those following this thread (Eric) what I've discovered so far.

I hooked up the new smoke test machine today and found a leak in what I believe is the throttle body elbow at a vacuum connection. I am thinking this is the air assist connection? I really don't know. I'm in research mode now. If anyone can review the attached pictures and advise me that would be greatly appreciated. Mainly I want to know HOW to fix the leak.

One picture is of the auto inspection camera (boroscope?) screen and the other picture shows the leaking connection point pretty much at the center of the frame.

 

Thanks and appreciated, great forum, great members!

I will have a look at this myself in the coming days, but was just wondering if the leaking is obvious (after you located it with the smoke tester), or if you really need the tester to confirm it.

E.

 

The leak was not obvious, even after I knew where to look. The amount of smoke coming out was fairly significant, but there was no other indication of a leak.

Since the parts to repair it won't be here until next week I coated the area with a layer of RTV and retested. No smoke came out after the temporary RTV repair. When I test drove it though, there was only a minor improvement in the fuel trims and while it seemed less, the rasping was still present. Perhaps the temp repair is not that effective or perhaps there are still other issues.

I literally laid my head on top of the engine and revved to about 2,500 to 3,000 RPM. The sound honestly seems to be coming right from the center of the engine and only occurs at significant RPM. Frankly, it's not that noticeable in the drivers seat unless I am on concrete highway; much less noticeable on asphalt.

I'm not feeling like a very skilled diagnostician right now, lol.

 

Do you hear the sound if you blip the throttle?
I never noticed it on steady rpm, but it might very well be there.

 

The sound appears to be RPM related. Blipping the throttle would only do it if I blipped until it hit 2,500 or so RPM. When I'm above 70 mph I can't hear the sound at all, even if I floor it to pass someone and zip up to 90 mph. Either the sound is drowned out at that speed or the extra load on the engine prevents the sound.