Hi fellow XK8 owners. I really need your help.

I did a 90% full throttle sprint off a red light for 20 seconds, then coasted to a full stop at the next red light, only to find the idle was very rough and had dropped from the normal 800 to 550 rpm (in neutral, with air-conditioning on). From then on it appears I'm running on less than the full 8 cylinders and the power has been reduced by 30%. Opening the hood, there is no noticeable excessive engine noise or clacks. Upon scanning the codes, there was one P1396 (VVT solenoid left bank), which re-appeared intermittently, sometimes there, other times not there after erasing DTC codes. There was never any warning messages shown on the dash such as CHECK ENGINE or REDUCED PERFORMANCE, etc. And the primary & secondary chain tensioners have not been replaced.

I suspect one (or more than one) of the sparkplugs and/or coils has failed. How can I detect which one has given up?

Any advice on remedying the situation is highly appreciated.

 

You have a 97 Jag xk8 and the tensioners have not been changed and you are driving it like that. TICKING TIME BOMB. When you find this fix to the current issue i would be on doing the repair on the tensioners, ASAP.

 

Sounds to me as if one of the secondary tensioners has given out and it's jumped a tooth on the chain - I'd remove the valve covers and check the timing. As stated above whatever the outcome those tensioners need to be changed asap.

 

I would agree that you prob have a jumped tooth. I would not start the car again if I were you, the next start could be the last for that motor, REALLY!

 

Curious, how many miles on it?

 

It has less than 80,000 km on the clock, which is under 50,000 miles.

The sprint was a rather gentle acceleration and not an instant flooring of the gas pedal and probably lasted for total 10 seconds or less.
We all have our crazy spur of the moment.

In my case, would you suspect it is the secondary chain or the primary chain that has jumped a tooth?
After lifting the cam covers, what do I look for to positively identify a jumped tooth situation? If that is the case, would it be necessary for the timing cover to come off for the remedy? Thanks for any advice.

 

You should only need to be concerned about the secondary ones at the moment, Read this to get a idea of what's involved
https://www.jaguarforums.com/forum/x...ners-how-4747/

Though since you have a very old XK at some point you will need primary's done as the guides where and crack, this is it won't blow your engine as the secondaries will if they give out, you can check for a skipped tooth by aligning the flats on the cams.. again see above post.. Good luck

All that said you may also have a stuck VVT this would cause the car to behave in such a manner, do a search of this forum for VVT and you might find some answers..

 

Bloody plastic secondary chain tensioners.

Bloody plastic secondary chain tensioners replaced. Damn.

Cat is now running smoothly with new NGK Iridium plugs, hahaha

 

Here you go, the damn plastic secondary chain tensioners:

Both had their plastic "pushers blocks" disintegrated due to old age (18-years) , and their plastic tensioner bodies have hairline cracks as can be clearly seen from the photos.

I'd been really lucky to have gotten away without a total engine write-off...

 

It would be a good idea to drop the pan and get the pieces out, they end up in the oil pickup screen and can reduce flow.

 

Now the next project: To protect the A drum in the transmission you should replace the main pressure valve with the ZF upgrade.

http://www.jagrepair.com/images/Auto...%20ZF5HP24.pdf

 

You seemed to have read my mind: I was just thinking of doing some belated maintenance work on the ZF, namely replacing the transmission fluid and the filter, the latter is available from Amazon.

Can you advice the best place to get the ZF main pressure valve?

 

If you have a ZF dealer that's the best choice. I got mine from a California dealer.

Main Pressure Valve 5HP24 - 5HP30