www.jec.org.uk

Hi

Could I get your opinions on what could be the cause of the noise and miss fire on my XJ8 please? Sorry for the long post.

This is a Video of the noise.
https://www.youtube.com/watch?v=GqvV8GY-9vQ

Everything was running smoothly until Friday morning. I noticed it was a little rough when it was started but just put it down to being cold. I drove to work, about 50 miles on B roads, due to rough roads did not notice anything different. Once I got to a section of dual carriage way and I was cruising with light use of the accelerator pedal I noticed a slight vibration. Once stopped at work it was obvious that the idle was pretty rough. I checked for OBD codes but it was clear.

I ran steady home that night it drove fine up to 55mph then stated to miss fire a little so I just took it steady. Idling is lumpy and there is a high pitch electrical type whistle and a rubbing noise. The video is pretty much an exact replication of the sound.

I've taken each of the coil packs out and checked them, physically nothing stands out. There is no oil in the plug wells. I have checked best I can the breathers and pipe work from the air box to the throttle body. All the injectors seem to be firing correctly. I've used a big screwdriver on each and put an ear against it and the noise does not seem to be from them. The noise also does not seem to be from the timing chain / cam sprocket areas. It does seem louder from the water pump area. All tested using ear and big screw driver. I've taken the belt off and checked the water pump and other pulleys and started it up for a few seconds and the noise is still there. So that rules anything belt driven out.

From more reading and searching I have possibly come to the conclusion it may be the timing chain(s). I haven't popped off the cam covers yet.

Above 1000rpm it runs smoothly apart from the noise, the miss fire is a lot less.

Anything I have been thinking about can't explain the noise only the miss fire.

Thanks

Do you know for certain if your car has the latest aluminium bodied top chain tensioners? With a failed plastic tensioner, they have been known to jump a tooth on the short chain which goes between the inlet and exhaust cams, especially on start up. This gives rise to lumpy running. If it jumps another tooth, then it can wreck the valve gear as it's not a 'clearance' engine. Sorry to be so negative, but it needs urgent investigation to be certain.
Any coil on plug unit would throw a P 035X code and that injector would shut down with a very noticeable misfire and restricted performance message on the dash display.

The right hand cam cover is the easiest to remove, after the air box and pipe work

Hope you get sorted.
Ian

Thanks Ian

I'll pop them off to take a look.

Darren

rough running can also be attributed to the breather pipes from the valve covers allowing air in due to being damaged

these pipes are readily available from Jaguar, and the pair will cost around £30 ,

so , along with the above good advise, i would check the breather pipes first ( they go to the TB , and unmetered air could be entering the system causing the ecu to wrongly fuel the car )

BB

Thanks BB, I think I have found the problem.

I do believe the top is missing off this!


Clicking noise and rumble metal chain on metal tensioner.

It looks to have over extended pushing the chain up and moving the position of the timing. I don't think its jumped as well. You can see the right hand cam in the picture is approx. 1/4 inch further over going by the flat sections and the bolts in front.

The right hand side looks fine


The primaries also look fine. This is the left hand bank.


The red underlined bit is a chunk of the top of the secondary. The cross is nothing but a bit of sealant.

I'm not going to leave it as it all looks fine they will all be changed but I think the cause is limited to the secondary on the left hand bank.

Thanks for your help just have to sort it now.

Hi Darren

great pics, and well done on finding the issue, you can see my post on the XJ8 forum on when i replaced my tensioners around ten years ago

this is however the reason why people MUST inspect the tensioners to see if the updated metal versions ware installed, and not wait for the noises to start , as by then its usually too late ,

once the work is done, i would get the oil changed and a new filter as well, as it will be full of debris

other than that, your engine looks in great condition , and well worth saving


BB

http://www.jec.org.uk/forums/viewtopic.php?f=86&t=3324

here is the link with pics

BB

Thanks BB.

I had planned to pull the covers off in the summer and do some other jobs but as you say this shows the importance of not putting this off.

I found your post some time ago and had been studying it in preparation for this task.

It was only just at Jagtech for a service last Monday but I'll drop the oil and filter as this all happened 200miles after that.

Just out of interest what are the upright metal cylinders with back tops in front of your cam sprockets?

Yes,
It's always the left bank which has the issue first as the slack on the chain is always resting on the slipper and just 'grinds away' at it. On the other bank the slack is dangling under the slipper with a gap between it and the slipper face.
No comfort though but at least you got there before any further damage. You will get a bit more acces with the air box out of the way, there's only the one 10mm nut at the top rear and then it pulls upwards out of 2 grommets in a bracket.
Definitely worth saving another 308 and good that you are doing it yourself - the cost of a garage job is the reason there are so many scrapped and as BB says yours looks fine internally.
Ian