Hi all

I bought my XK8 just a few weeks ago, knowing it had a short MoT and that in recent years emissions have been an issue. I put it in for a test at a local independent garage, and sure enough, failed on emissions.

2 new cats, 4 new O2 sensors and a 1k bill later I picked up the car.

It had now passed emissions, but on the test drive (!) developed a misfire. That is the story they gave me at least!

Garage made it pretty clear they are accepting no responsibility (we'll see about that once I find out what is actually wrong), but until then I have a car misfiring horribly.

Diagnostic shows misfire on cylinders 1,2,3 & 4, general misfire and cat damaging misfire. Looking online, a common cause for this is the secondary timing chain. As the car has 135k miles on the clock and nothing in the history to suggest the tensioner issue has been addressed, this seemed like a likely cause. Called a local independent specialist for advice, he seemed to agree that the cam chain was a candidate, and probably wanted doing anyway. Offered a complete cam chain change for just over a grand which seems pretty fair, but not available to do the work for 6 weeks. If need be, so be it, but I decided to have a look and see for myself if it was indeed the cause. Apart form anything else, another grand spent just in case is not all that welcome a prospect at the moment.

So today I have taken the timing covers off of the engine. Yes, plastic tensioners, but they seem in really good condition and all 4 flats on the cam shaft are spot on alignment. Turned the engine over by hand 360 degrees, no tight spots, no unpleasant sounds at all. So not the cause of the misfire, but needs those tensioners doing, and now is as good a time as any with the top off the engine.

So my first question - I can get OEM metal tensioners from ebay easily enough. I ordered a kit with both tensioners and screws. What tools do I need to fit the tensioners? As it's likely to be a one off use, are there workarounds or is it worth the cost of buying the tools for a single use?

Second question - what are the likely causes for a misfire? While under the covers I can see that the coil packs are all (at least visually) in good condition. No oil/water in the compartments. I will pull a spark plug to examine that, but I am pretty sure they will be OK also (unlikely to go from a smooth running engine to 4 bad spark plugs overnight). I have looked around the area of the cats/O2 sensors and I cannot see anything damaged or loose, so I am very much open to suggestions.

 

Now that you have the cam covers off, the only extra tool you need is a cable tie:-

https://www.jaguarforums.com/forum/x...acement-82231/

I wouldn't buy the tensioners on eBay, try someone like SNG Barrat.

 

cat clogged on that bank maybe

 

Cheers for that. Ordered from SNG Barrat. Cheaper than ebay too!

I'm not exactly clear what the cable tie method does. It it just to lock the chain to the exhaust cam?

 

I sincerely hope not, having just paid £1k for 2 new cats!

 

Yes, holds everything in time.

Out of interest, what year is your car? Suggest you put model details in your sig.

 

Thanks for the advice so far. All on track(ish) although I managed to sheer one of the screws on one of the cam covers (my stupid fault) so I can't finish the job just yet until I get replacement screws. All back together as far as the timing goes, 1 full rotation of the engine by hand no fouling, no noises and all 4 flats finished back in line, so all the signs look good.

both tensioners had cracks, 1 worse than the other so worth the heartache, even if it has been more heartache than I anticipated!

Fingers crossed the misfire has magically disappeared, but without having found anything wrong, I am not optimistic about that.