LS1 backfires help plz

[adamc11]

Hi..
My friend has a WL caprice 2004 v8. It's an auto. I believe it has been modified by HSV (it has a HSV plaque in the engine bay, and i think that possible the intake and/or exhaust has been modified). Other than that it is stock.
Anyways to the problem...
It backfires if your in neutral and rev it. It is even more noticeable if you start it and rev it straight away (i don't mean if it's cold, i mean turning the engine off and starting and revving). You can also sort of hear it when you push the brake and accelerate (sort of a put-put sound, hard to explain). Taken it to a holden dealer (mantello in fawkner) a few times and they havn't been helpful at all, they say they can't hear it, and then when they heard it by me showing them, they had a 5 min look and then said they couldn't find the problem. I doubt if they even looked at it, but i was in a rush so i left. I think they were trying to push the car out of warranty, which just expired or expires very soon.

Anyways, any ideas on what is causing the problem?

Thanks,
Adam

[BANKS]

Hi..
My friend has a WL caprice 2004 v8. It's an auto. I believe it has been modified by HSV (it has a HSV plaque in the engine bay, and i think that possible the intake and/or exhaust has been modified). Other than that it is stock.
Anyways to the problem...
It backfires if your in neutral and rev it. It is even more noticeable if you start it and rev it straight away (i don't mean if it's cold, i mean turning the engine off and starting and revving). You can also sort of hear it when you push the brake and accelerate (sort of a put-put sound, hard to explain). Taken it to a holden dealer (mantello in fawkner) a few times and they havn't been helpful at all, they say they can't hear it, and then when they heard it by me showing them, they had a 5 min look and then said they couldn't find the problem. I doubt if they even looked at it, but i was in a rush so i left. I think they were trying to push the car out of warranty, which just expired or expires very soon.

Anyways, any ideas on what is causing the problem?

Thanks,
Adam

If i start mine, leave if for about 10 seconds then boot it in park it backfires, i'd say just getting rid of some unburnt fuel. But thats the only time i can do it, only on start up and just once.

Pretty sure if you report something in the warranty period, and you complain again on the same problem after the warranty is over, they have to fix it

you should be able to find out the warranty period from holden