The other day, I stared my car (1998 XK8) and it stated fine and ran smooth just like it always does. I went to the Bank and while I was sitting, the engine sounded funny and it started to stumble at idle and did not want to pick up the fuel when I gave it gas.

Car was not over heated and then I noticed the red and yellow awarning lights were both on and the message center said the engine was in safe mode and the abs failed and the traction control had failed and the trans was in safe mode etc. etc. and then the car stalled. I re started the engine and started for home.

I nursed it home ( stalled two more times but started up without a problem) with both warning lights on and the message center telling me several major systems had failed or gone into safe mode.

I got home, shut the car off, let it sit for 2 minutes and restarted the engine and the warning lights were out and the car was running like it was brand new again. I have driven it several times since then and it seems to be fine now.

Does anyone have any idea what happened?

 

How old is your battery? If it has some age on it, you may want to replace it. An old, low battery can lead to the symptoms you posted.
Vector

 

I was going to say the same thing. It sounds like the battery is going and Jags don't like a weak battery.

Mark

 

There have also been a couple of cases here of the heavy B+ cable that is bolted to the left and/or right dashboard fuseboxes starting to loosen causing similar symptoms. Worth a check....but be careful not to tighten those without disconnecting the battery first to avoid a welding your wrench to the chassis!

 

Question,
I thought when the car was running that the altenator supplied the 12 volt power to run the car and all it's gadgets, radio etc. and then a little more for recharging the battery power that was used when the car was not running.
So why would a battery cause these troubles if the altenator was working properly?

Like I have always said I am not a mechanic.

Happy Motoring...

 

A bad battery can pull a lot of juice from the charging system trying to replenish its charge, not leaving enough for the many electrical systems on the car to function correctly. The modern electronics, computers, etc on a Jag don't like not having enough power.

As for the alternator and the battery, if you have a bad battery, its like pouring water into a bucket with a hole in the bottom - you are never going to get it full (charged.)
Vector

 

What Vector said.

Also, I the past, I've had some vehicles that wouldn't run without the bad battery (as opposed to no battery). While I don't fully understand why, these vehicles could be jump stated or push started (manual transmissions) as long as the bad battery was left in. However if battery terminals were disconnected it couldn't be started (through jumping or push start). Also, once started, if the battery terminals were disconnected, it would stop. Anyone know why?

I've also had vehicles that would run without a battery if jumped or push-started (this makes sense to me and this is what I would normally expect).

 

The battery will act like a ballast to smooth out the voltage even if it isn't completely healthy. You've likely seen a fluorescent light with a bad ballast flickering and carrying on and similar things will happen in a car.

My guess as to why it won't run is that either the charge circuit for the alternator is seeing these voltage spikes and cutting off or the electronics are going into a safe mode because of those spikes.

Cars these days are built expecting a good battery and constant supply of voltage. When it isn't there they do all manner of weird things. This has been one of the biggest hurdles to electronic engine controls in light aircraft. In a small airplane there is an alternator for all of the fancy electronics and a stone age magneto to run the spark so that no matter what happens the engine will keep running.