Greetings fellow XJ8/R's! My name is Robert Brooks and I have recently acquired a 2001 XJ8 Base. The engine has 147K and had the timing chain problem melt down in 10/2010. Whole engine redone secondary to what happens with the chains jump/fail.

While test driving this car I did not notice a slight tapping/knocking coming from the engine from time to time. Once I got it home and was checking it out the problem was detected. Now first, I have been a car guy since high school and have restored and owned many types of automobiles. I have done lots of work on cars myself and have a nice garage set up. But I have zero experience with Jags so . . . .


The problem is variable and sometime does not present at all.
The engine does run out good and it sounds to be running on all cylinders.

Here are the symptoms:

1. Smooth start up with usually no tapping or knocking.

2. Tapping/Knocking starts after about 1 mile of driving. It does increase on acceleration until 1200 rpm as the car accelerates to past 20 mph. Knocking is most pronounces with car stopped in neutral or drive and at idle.

3. Tapping/knocking last for about 6 miles then stops. Maybe only slight ticking heard at that point.

4. After that engine lopes some at idle. Sometimes it doesn't. Minimal ticking. If the engine is loping at idle and the engine is accelerated it seems to abate some but eventually returns to the lope.

OK experts, I can't wait to hear your comment. Thanks in advance for any help, comments or funny jokes!

Robert

 

Did the guys replace the entire engine with a new one or was it able to be rebuilt? You should find out what exactly they rebuilt. Could be a timing chain guide that is clicking or a tensioner? In 2001 its unlikely but you never know. You don't have a VVT unit so can't be that. Could be a lifter...or valve tap. Post a sound clip so we can hear it.

 

Thanks for the response Coastal!

I wondered about the variable timing. Thought some electronic unit might have been going bad - what years were the VVT? I am not sure about if the engine was changed. The guy who sold it to me was not as forthcoming as he should have been. I am going to call him tomorrow and get better details. I know there is an estimate sheet that came with the car's papers that shows a total rebuild of the engine because of complete failure of timing system and valves, etc dated 10/2012. Estimate was $ 5400 to repair. The guy I bought it from has another mechanic do the job but for about $ 2800. I will try to check but the guy may be too guarded.

I was leaning towards a rocker arm and/or rod problem or maybe even a broken valve spring (but I would not think the sound would go away with the broken spring). But the arm or rod I think that would explain the symptoms. And from my reading on this list there are not hydraulic lifters, correct?

What does the engine loping suggest?

What's the best way to post a sound file?

 

IMO, engine loping suggests a problem (leak) in the vacum system, and or TB issues. Ticking/knocking will be hard to diagnose. Experienced Jag mechanic will be able to pinpoint it with the stetoscope,....almost impossible to locate by recording, and posting over here.
I would bite the bullet, and take it in for diagnostics (money well spent, otherwise it will be a wild goose chase!).

 

Thanks Daniel - your advise is heeded and was what I was planning on doing anyway. Just was getting some ideas before hand.

Just for fun tho:

OK, did a little Youtube video. You can really hear the knocking. Honestly, the knocking sound is amplified 2X in the video. Mike on camera must be sensitive to picking this up.

Also, knocking is not 100% isolated to the point that I point to. It's just that I can feel it when I hold the timing sensor (???).

As stated before, this goes away after about 6 or so miles of driving. For the life of me I can't figure out why it goes away.

 

Yikes! If it was my car, I'd be very reluctant to run it any more without opening up the front of the engine. If indeed your year doesn't have VVT, you're up against some kind of tensioner issue, and that would be very expensive should it fail.

 

Thanks Rob,

Any idea why it stops after about 6 miles of driving?

 

These engines don't have rocker arms or hydraulic lifters-the cam lobes bear directly down on shims, buckets & valve stems/springs.

Tapping noises seem quite common now on these engines & as yet nobody's pinned down an exact common cause, so it's very difficult to diagnose from a distance.

My 150k mile XJR makes a light tapping noise several seconds after start-up & it's gone when the engine is warm. Raising the engine speed quietens it down & also putting the car in 'D' makes the noise much quieter, which leads me to wonder if it's load-related & perhaps widening big-end clearances?

There have been occasional reports of no 1 big-end bearing failing if the oil level is allowed to drop too low & the car cornered hard-this can cause tapping noises. I did notice that keeping the oil level at maximum or even slightly above does quieten the noise down a lot.

There have been various specifications for the oil level/sump capacity on the V8's over the years-with matching dipsticks as the spec changed.

I would suggest keeping the oil level at least at the maximum level & maybe a bit over as well-about half a litre over can help quieten down the engine...

 

Mine made a similar type noise and the dealership said it was caused by the chain slapping due to a chain guide being broken.
Changed all the primary and secondary tensioners and chain guides and the noise went away.
My take on the noise going away after 6 miles is that the oil pressure is then sufficient to offer some resistance to the chain and prevent it slapping about the place.

If I was you I would open the valve cover and have a look see. With that type of noise there should be something visible.

 

The 4.0lt normally aspirated all have VVT and the only difference between AJ26 and 27 is the placement of the pickups for the VVT.

I'd have a look, I suspect a lazy tensioner on that bank, something's stopping it from tensioning on start-up.

These little units have an oil gallery that pumps them up. Something as simple as the wrong (heavier) oil can cause issues such as this. I use a 285,000 mile supercharged engine as an example of how it can use the factory recommended 5W30 semi synthetic without knocks or ticks and rattles. Yes that's twice the mileage of yours, and got home from the moon, yours is still there, mileage wise of course, nice to know it'd make the journey though lol

I wonder if it's got cheapo 10w50 in it (whadda had in the garage...at some point).

I would open it up and see if the tensioner/guides has worked loose, in fact I'd just have a look, it's 8 and 10mm sockets it isn't even the dipstick side (easier side to work on, header tank etc...)

Post a video of the engine after warm-up back in the garage when the noise has gone.

Another aspect of these engines IS the VVT - when you say revving to 1200rpm clears the tapping, that rev range activates the solenoid to swing the cam, so this could be failing, it just so happens a I have a pair of them for this exact engine, but we need to confirm this first...

Any check engine lights on the instrument cluster?

Last thing, can you introduce the car as a 'Jag-U-Arr' next time, as a Brit, we don't say it like 'Jagwarr' Cheers!

 

The odd thing about the light tapping on my engine is that I've had both cam covers off & the chains/tensioners are fine. There's no VVT either as it's the supercharged engine.

The noise is definately a proper 'rhythmic tap' & not like the unsynchronised rattling tap or slapping of a loose timing chain.

The other thing is that it's load-related, as applying the torque converter/gearbox load to the crankshaft makes the noise virtually disappear-as did using thicker engine oil in my last oil change & keeping the oil level at least at maximum.

It's mostly an irritation for a couple of minutes when cold & the car drives fine, being completely silent when warm. It may even be psychological, as in the more you hear a slight noise & focus on it-the more it grows in your imagination as an irritant, when in reality nobody else would even hear it

 

Thanks to all. Here are a few comments back:

Red: 10-30 regular oil is what last change was (by prev owner). I did top it off so it is above high point on stick thinking along the same lines you did.

Fishfoolbear: I understand your comments about taking a gallery a while to fill but 6 miles under load? That seems way too long. And that is with the engine under load, not just idling. Just commenting.

Sean B: As I am a newbie here. You are talking about taking off the "valve cover" on the passenger side. Does that expose the gears/chains also? And how do you check to see if the guides/tensioners are loose? Can the engine be run like this to observe the movements?

Additionally, as asked, there are NO warning lights. Is there way to check VVT? I tried disconnecting what looks to be the timing sensors on both banks (at idle) and that did nothing.

And FYI - I do say Jag-u-ah. Two reasons, we old time Charlestonians tend to have somewhat British pronunciations (or at least inflections) in our speech. So battery becomes BAT-tree, secretary becomes SEC-ra-tree, car becomes cahr. It is similar to the Bostonian accent but NOT as harsh and nasal. Secondly, there used to be a dealership her that has a British woman do the adverts and she always said "JAG-u-ah." r is almost not heard.


So Sean, should I also start with the near-side and off-side references too? I don't want to parse but I don't want to come off as some cheeky monkey either.

 

I have the similiar noise but I've had the secondary tensioners replaced myself and my chains are tight as they can be...no slack. My noise however, is from VVT on passenger side. I can rev to around 1500 and I hear a lil whirrr as it kicks in and its quiet. I have 10w40 synthetic in but I'm about to change the oil as people have reccommended thicker weight oil and a can of engine restorer to quieten down the VVT. Other than that this summer I may just get bold and tear the front of the timing chain covers off and just see what is entailed in replacing the faulty VVT unit.

 

So your noise sounds like the knocking like in my youtube video? That pronounced? And it goes away after 5 to 10 minutes of driving?

I am not sure what the "whirr" sound is.

And one person mentioned going to a thinner oil. Now I am really confused.

 

The 'cam timing sensors' you disconnected where the VVT pickups. You've some research to do I guess. The actual cam sensor(s) are located at the back of the cams against the bulkhead. The early AJ26 engines have 1 the later AJ27 have 2 cam sensors by the way, yours being an 01 should have 2.

To remove the cam cover you have to first remove the coil pack cover, undo the coils and pull them out laying across the top of the engine, then undo the cam cover bolts and lift the cover off. You can then inspect the state of the upper tensioner and chains and crucially the timing.
This is done by turning the engine clockwise on the crank damper bolt until the cam flats are lined up - these flats are, looking at the cam drive sprockets and going back towards the windscreen a few inches, there...you should be able to get a straight edge across them to confirm timing is correct. If this checks out ok, tensioners in good shape, then it has to be faulty VVT solenoids.
Search this forum for changed timing chain tensioners, lots of pictures and lots of information, like I said, a bit of research and you'll be 'one of us' and offering advice in no time.
Changing oil weight is a band aid and doesn't address the issue. And there is one.

 

Jaguar's own detailed technical description for the operation of the VVT units states that their performance is affected by oil property & temperature, so the oil weight does have some bearing on operational performance.

Jaguar actually state that VVT operation may be impaired by high oil temperatures which cause a lower oil viscosity & therefore lower oil pressure to the VVT units.

Source: Jaguar Publication JJM 18 15 18/90, July 1998

(XJ and XK Series 1999 Model Year Update-page 15 "Engine Oil Temperature")

 

Continued thanks to all!

Sean,

Right, a little investigative work indicated that the engine was rebuilt after a secondary tensioner failure in 10/2010. I talked with a Jag Tech (moderately trained) who had looked (within the last 6 months) at the new work done on the chains/cam/tensioners/etc. at the request of the previous owner because of the knocking noise. He indicated to me that all the work looked correct and tight. He also said that he had removed the pan to see if any obstruction was near/on the oil pump and none was found. The previous owner declined the offer to further investigate the problem.

Later I talked with a Jaguar/British Car shop owner (23 years) and he is going to look at the car in a couple of days. He was very nice, well trained and has been involved deeply with the British Car Club in my area for as many years. I feel I need to call in a specialist with this. BTW, when you said it may very well be the VVT solenoids; will there be a specific way to test those? Or is that a process of elimination?

 

Judging by the fact that both XJ8's & XJR's can produce this elusive knocking/tapping sound, the fault may not even be in the VVT system as XJR's do not have VVT units but can still tap or knock.

Valve buckets & shims/big-ends have been suspected of producing this noise & I believe that Racing Green (UK) have dismantled Jag V8's & found that number 1 big-end bearing has failed on some of them due to oil starvation.

Their advice with these engines is to never let the engine oil level drop to the minimum mark & always try to keep the level at least at the maximum mark on the dipstick.

 

@Red
From reading this, are you suggesting wear to the number 1 big end bearing?
Does your knock sound like robertjag's engine?
Does your car hunt/lope?
has your engine had the timing parts update?

@Robert,
I've never heard of a 'moderately trained' Jag tech! I've removed VVT units from these engines and ran them as per supercharged, with no VVT attached. I wouldn't recommend doing this to your engine though (added parts required)

So, the moderately trained tech checked and confirmed everything was good, with the noise present. Did he comment on the hunting at idle?

If there's no OBD engine codes, there could be an upstream air leak, i.e. the two gaskets on the throttle body, the first is the rubber one the induction tube snugs down onto the throttle body, the second is the metal one underneath the throttle attached to the intake elbow. Also a crack/split in the induction tube. All 3 need checking. Easy job. 10 minutes with a 10mm/13mm socket/extension (from memory)

But as you've felt it could be timing as mentioned in the video, you know that the VVT plays a part in timing of the camshafts, and if one is lazy or sticking it will be a few degrees out on the intake camshaft, and may be a cause of the hunting.

Pure speculation as I'm not with the car. But I've given you enough information and items to check to sort this issue out.

 

@Sean,

Thanks for the continued input. By "moderately trained" I will explain: the independent shop is actually for German cars but they have a father/son team that is working on Jags there too. I talked with the son and, while he seemed fairly knowledgeable, he had some hesitations which made me question his experience. I am pretty sure his father is Jag certified.

And no, he did not comment of the hunting.

I did end up scheduling with a Jag/British car shop where the owner (23 years experience) is going to look at the car tomorrow.

So a question or two, I am understanding you taking about air leaks in the three problem areas. But would those leaks cease causing a problem when the car is warmed up thoroughly? I have looked for a tight fit around the throttle (??) intake as the plastic tube is damaged where the 10 or 13 mm bolts hold it down. It does not seem to make a difference tho as there is a nice, tight fit.

At this point I don't know much but I am leaning towards VVT. The knock does go away around 1600 or so rpms. But maybe the engine noise is just drowning out the knocking.

BTW, when I crank the car, cold or warm, the rpms jump to about 1100 for about 8-10 seconds. I assume this is normal to keep the car from choking/stalling on start up. But after that the idle rpm drops to about 750-800 (by dash gauge reading) and THEN that knocking starts. This is repeatable.

Just more info. ANY comments on why you think it goes away after warmed to operating temp with your suggestions is very appreciated.