Hello all,
Long time lurker, first time poster. Just recently, I purchased a 2000 Jaguar XK8 with 114k miles. I got it for a good price, but it has a bit of.. deferred maintenance which I am just now discovering. Initially, after I got it home and stuck an OBD reader onto it, it gave a long list of codes, which boiled down to needing a coil replacement on cylinders 3 and 7, which were both misfiring. After I replaced the spark plugs and the coils the misfire(s) appear to be gone... However, there is still a problem which only seems to manifest itself after the car is running for a bit more than a minute or two. It begins to run roughly, and displays "Failsafe Engine Mode", as well as ABS Fault and Gearbox Fault messages. (It gives no codes, however.) Around the time Failsafe Engine Mode "switches" on, the tach and the temp. gauges fall to their minimum position, and the red brake light near the temp. gauge comes on. It also makes an air hissing/sucking sound (this also turns on only when Failsafe mode engages). This sound seems to originate from the driver's side, somewhere underneath the car.
Any help/pointers would be greatly appreciated, thanks!

 

I would start by checking the underside of the intake bellows first followed by checking the connection by the throttle body.

As far as your CEL on, I would start with key on engine off and clear all the codes. After that, I would perform a hard reset. Disconnect negative cable first then positive and tough both disconnected cables together for 15 seconds. Reconnect positive first, then negative second to see if that helps your instrument gauges before you go any further. Good luck.

 

Vacuum leak. Check driver's side bulkhead, there is a plastic tube that is somewhere in this area, that cracks and causes a leak, also there is the accordion section of the air intake that develops cracks that are hard to see and find, that open and allow unmetered air in, or a vacuum line has been dislodged while changing the spark plugs and coil packs, this is most likely; check around it may be as simple as plugging a vacuum hose back in. Check the diy sticky for a vacuum line diagram, print and make sure they are all hooked up, the hissing is a giant hint, but I would definitely be looking near where the work took place. As for all the warnings, they should clear when you address the leak that they are responding to in a sort of 'domino' effect where one component is not getting what it wants/needs and throws everything else off down the line that depends on accurate info/vacuum line pressure, from the previous component and does not get it, and throws it's own error, but no code.

 

You will probably get better help from folks with the same engine model, but I would also check all the emission-related stuff under the wheel well liner. If the noise is that loud, it should be easy to find.

Also, in the back of your head, keep in mind the the earlier cars were occasionally prone to throttle body issues. Being throttle-by-wire, they are fairly complex but also heavily monitored and therefore can help you in the diagnostic with a lot of codes. Separately, if it comes to that, they can be rebuilt without breaking the bank.

Best of luck, keep us posted.

 

After reading the title of this post, I was going to congratulate you on your new boat. One of those will suck the money out of your wallet faster than a Jag will.

As for your peculiar collection of problems, a combination like that, aside from the hissing, could be the result of a weak battery.