There are several possibilities for this. The usual culprit is that the timing is off. Make sure all your plug wires are correct. 1-8-4-3-6-5-7-2 in a counter clockwise turn.
I would suspect it is not timed correctly.
It sounds as if your engine may be out of time, I would check for a sheared flywheel key.
Possibly the firing order got messed up.
sounds like you need a tune-up
Never mind thanks anyway turned out to be a bad CTS
my alarm keeps going of and wont start.
The term 'dead engine' is usually meant to refer to an engine that wont start. The symptoms are that the engine does not start, the starter might turn it over, but that is it. No firing, no backfiring, the engine is effectively 'dead.'
Check the crankshaft sensor. Also check the timing and timing belt. The backfiring indicates that the engine is firing at the wrong time.
start by having the computer (PCM)troublecodes scanned. Autozone will do this free of charge.
check for broken or slipped timing belt...also fuel filter and fuel pump Also check the orange wire connected to the positive battery terminal. If it doesn't have a good connection the engine will turn over but will not start. Had the same problem with my '90 lemans.
when you unhook the battery the computer probably resets itself.
Simple get the 4 liter engine instead more power and better MPG runs quieter and everything