range rover 4.6 backfiring

Hi still need help with a 4.6 range rover m reg , back fires and only just runs for a few seconds but is very erratic, backfires when turning over .
replaced the coil pack,plugs, leads , compression check is fine , fuel pressure fine , cam and crank sensor fine. clean fuel, had a crypton tune guy out but the computer plug in is not recognising his machine so he is a bit limited however all the checks above have been done .
is it possible to slip a tooth on the timing chain?
it would appear that the firing order was wrong as it sounds like its running on crossed leads but they are in the right order.
could the new coil pack be duff?
help !!!!! its my 1st range rover and at this rate it might be my last

any help will be appreciated
rob

When was the last time it ran? Stale fuel?

It is perfectly possible to get a 'new' coil pack and still find it to be duff. Check all of your earths as well as that can do all sorts of strange things!
Andy.

check your crank sensor,i had one with similar problems.the crank sensor moved in and touched the flywheel and didnt know when to fire,i put a couple of small washers between the sensor and mounting holes to space it back out worked perfect.you will know if it has been rubbing the flywheel as there will be score marks on the end of the sensor.it is the actual sensor mount which can drift inward,it looks like a big core plug.newer ones are welded in place so cant move im sure.hope this makes sense.also you might need a new sensor if badly damaged.