My 97 XK8 started running poorly and the yellow warning light, Engine Fault-Poor Performance warning came on. I can find nothing in my manual that mentions this warning? Does anyone have an idea what is going on?

 

Read the OBDII codes then post them for us to see then we can help you.

 

could be a number of things - best bet would be to go to Advance Auto Parts or Autozone and have them read codes and check the battery/charging system. Weak or OLD battery can cause a ton of electrical gremlins. Post the codes here and you will get guidance on how to proceed

 

I can't get the codes it keeps saying error.

 

Check 5a. fuses #10 and 13 in the drivers side facia panel. That's the panel you see when you open the door.

 

I checked the fuses and they are all good. However: it has been sitting and now the battery is dead. I don't know how old it is, but it would seem I need a new one. Do I need a Jag battery or can you use a different brand? Will disconnecting it and installing a new one cause any problems, like needing to reprogram everything?

 

The battery will go dead when you leave the sitting for more than a couple of weeks. It may just need to be charged. It's best to have a battery tender connected if you are not going to be using the car.

If you do need to replace the battery you will not have to reset anything, unless your radio requires a code, not too common in the US.

 

A good battery will go dead after a few weeks of sitting???? New one on me.

 

Sounds like it may be just a old battery issue, if they are pooping out, they can cause the car to do stupid thing including running wrong. Seems these cars like healthy batteries to make all of its components to work right.

 

Or a drain in the battery. Charge it then go to any parts store and ask them to test the battery in the car. When they do that they will also check the charging system. It would be 2 things you will not need to worry about if they check out ok.

 

also if the engine sputtered after sitting on the start up it may have triggered the knock sensors and mine wouldnt clear itself afterwards . finally i replaced both cleared the codes and no more codes... also my battery will go dead if it hasnt been running for a few weeks . just bought a solar battery charger at wal mart for 20 bucks. hope this does the trick very strange tho if i plug it into the lighter socket the raido works with the key out ???

 

you need to find out why the battery is going dead it should not go dead in that short period of time.

 

An older battery can do that, Gus, but not a healthy one. A couple of forum members have reported that issue.

 

I agree with the old battery however, an unknown draw will kill a battery in short order as several have experienced. It is always good to take the car to a place to have the battery and charging systems checked. With today’s technology it is easy and most of the time free for the asking.

 

The battery is at least 3 1/2 years old, that's how long I have owned the car. I am charging the battery and will take it to Advance Auto Parts to check the battery, charging system and read out of codes. Thanks for all of your help. I love this site and the smart folks on it.

 

I'm surprised that nobody on the forum suggested that your problem might be a bad coil. My wife's XK8 is currently in the shop for a coil replacement. She got the check engine light along with the "restricted performance" message.

 

At the beginning of this thread it was suggested that he have the codes read. A bad coil would result in a code for the cylinder with the misfire.

 

If you can measure the standing current leaving the battery when the car is at rest they are (in my car):-

Trunk open (light on):- 1 amp @ 0 seconds
Trunk closed:- 490mA @ 0 secs, then 400mA @10 secs, 27mA @ 1 min.

All times after ign. off & key out.

I have a sneaking suspicion that the old battery problem is due not only to slightly lower voltage, but also that the battery has less decoupling (as it doubles as a giant capacitor) of sproggies on the electrical busses, therby confusing some of the microprocessors.

2 weeks charge doesn't seem very long - that's just a vacation stay at the airport car-park

 

3 1/2 years is a pretty good life span for a battery in Florida - the heat is hard on them.

 

Charged the battery and got the following codes PO-405. PO-406, P1111 P and the knock sensors which it's had for awhile, but it ran fine. My mechanic says the newer ones go into limp mode because of the knock sensors, but not 1997's like mine.