Intake Backfiring

[Nathan]

Does the CIS intake backfiring(blown air box) only occur at start up, or can it also happen at engine shut off?
I have read other posts about blown air boxes at start up but not at shut off.

[Lorenfb]

A lean mixture will cause an intake backfire. Also, if excess cold start fuel
is injected, this may be a real problem. If one holds open the throttle at shut
off at a very high engine temp, a backfire may occur, e.g. piston carbon buildup
which is very hot causes intake fuel to ignite with intake valve open.

[Nathan]

Thanks for info Loren
Also how loud does the back fire has to be to blow a air box?

[Lorenfb]

Any backfire is not good.

[Nathan]

Loren I had retarded the timing just a bit because of a metal to metal pinging/rattling noise that my car is making at idle thinking it preignition. It didn't seem to help. I think the noise has something to do with fan/alternator assembly cause I'd remove the belt and it goes away.
When pull the belt the engine begins to sputters I then turn off put back on and no sputters but rattling noise starts again. So I went around the block to see if goes away and no I turn off and I hear a mutted back fire
I'll check in the morning to see if my air box is ok and to return the timing back to what it was. The engine was sitting for 2 months up for oil repairs just recently installed on Wednesday. IT ran good and had power before the repairs but now hardly any power even before retarded the timing on Friday

[dean]

I would also check the fuel pressures. It could be lean. I hope you are not driving around the block with no fan belt. Check the alt bearings for play also