Ecotec backfiring

[Jonah 101]

Hi, before I start Im just gonna say i search hard to find something that is like my issue but i cant. please link if you do so.

I have a ecotec VS, 210,00kms on the clock. when the engine is warm it back fires when im parked up and give it a blip on the gas, but today went I did it it went bang out the exhaust then bang out the intake. I figured this rules out a burnt exhaust valve or anything. I noticed it doing it a while ago but i thought it was because of the hole in the muffler, that is now fixed and it still does it. It not showing the engine check light but tommorow morning I will run a check. From what I have read in similar cases it could be the CAS, but it idles fine and does not misfire. starts easy too. Also could it be the harmonic balencer? o2 sensors are old I would say, not knowing as i havent had the car long. TB and MAF have been cleaned, thoroughly... new leads, plugs are fine. Injectors - I run a flush in the fuel when I got it. It burns a bit of oil but i think that due to the PCV in the plenum spewing oil. Its rather bad, probly due to my heavy foot.

Thanking in advance.
Thoughts?

[James39]

On mine I had the same problem which turned out to be a leak at the headers. When I put pacemaker extractors on the problem went away...

[L67 Calais]

By Gas do you mean fuel.... or gas?

[Jonah 101]

Okay, thats remined me there is a crack on the LH manifold. Maybe thats wher the bang in the front was. when I had her on the tune scope at school the Hydrocarbons were rather high. Im guessing thats from oxygen getting in before the o2 sensor. Thanks james!!! lol

By Gas do you mean fuel.... or gas?

Accerator pedal

[L67 Calais]

Ok...... Is it running on Petroleum or Liquid Propane Gas?

[Jonah 101]

Nah Petrol mate. In my search I found out about the joys of misfiring, backfiring LPG V6s lol