www.jec.org.uk

For the last 9 months the engine management light on my Supercharged XJR has been coming on, and the tester comes up with a misfire on all cylinders. The problem is that the car is running perfectly. On advice, I changed the air mass sensor as I was a told that sometimes it can give a false read. After resetting the light, it's fine for a couple of months and then suddenly comes on again. Has anyone encountered this problem and can give me some advice. Thanks. Jeff

Hello Jeff,
Sorry to hear your having problems with your XJR.
If you could tell us exactly which codes came up when you scanned the car that would give us a better start point at diagnosing the issue.
Also you don't mention which year your XJR is.
It all helps towards a successful solution to the problem.
On the information you have given so far I would be inclined to clean all of the electrical connections in relation to the ignition circuitry and then treat the car to a hard reset.(MAKE SURE YOU HAVE THE RADIO CODE FIRST)
Take care.
Andy.

Hi Andy

Sorry for the very late reply-I didn't see your post.

The car was registered in September 2000.

the scanner is - Snap On Modis Ultra

The codes are:

P0300- Random misfire
P0301- cylinder 1
P0302- cylinder 2
P0303- cylinder 3
P0304- cylinder 4
P0305- cylinder 5
P0306- cylinder 6
P0307- cylinder 7
P0308- cylinder 8
P1316- misfire rate excess

The vin number is- SAJAC15N61MF23821
The engine number is- MB0008292113

The mystery is that the engine is running brilliantly, smooth and quiet with no misfires.

If you have any other suggestions now that you have this information, please let me know. In the meantime I'll follow your advice.

Thanks

Best

Hi Jeff.
I would think it highly unlikely that all the plugs and coils would give trouble all at the same time,I would put my money on an intermittent bad connection somewhere.
Use an electrical contact cleaner and a small nylon brush when cleaning the connector blocks.
Also it is good to make sure the battery is always fully charged if the car is not used regularly.
Info on performing a hard reset is here(if your not sure what is involved)
viewtopic.php?f=86&t=15988&p=86700&hili ... set#p86700
Clear the codes and do a hard reset then use the car and see if they reappear.
Keep us updated on your progress if you can.
Good luck and take care.
Andy
P.S. That's a very smart code reader you have