Backfire on transition from full throttle

[manga_blue]

MB, my first thought when I read this post the other day was what's been done to your car recently, as my understanding was that the socketing & remapping performed successfully for at least 6 months?

The following provides a summary of socketing & remapping:
viewtopic.php?f=55&t=38209

That's true - it's gone like a dream right from the start until just recently. Something else has happened.

Air leaks(exhaust leak) in to the exhaust will cause a backfire especially with richer fuel mixtures.

I hadn't heard of that before but you might just have nailed the initiator for the backfire. Does a pinhole leak around the wideband sensor bung count? Still doesn't explain why it goes horribly rich in the pipes just beforehand though.

[StanTheMan]

well.....when you think about it
a leaking exchaust gasket will not cause a backfire but it will gurgle on deceleration.....at any speed. Not a back fire as such....but kind of sounds similar

[manga_blue]

Think I'm getting to the bottom of this now. Thanks for all your help. The car has 4-2-1 headers with a flexible coupling just in front of the flange to the cat. Yesterday the inside of the coupling failed totally so exhaust blows straight out through the metal covering mesh. The mesh used to give some muffling of the sound so you didn't realise how bad the leak was. It could have been there for weeks. It was bloody obvious when it finally gave out with me driving down Clyde Mountain with absolutely deafening exhaust popping and banging and echoing through the forest and fumes all through the cabin.

The wideband was reading AFR 22 most of the time, maybe indicating that air was being sucked back in through the holes betwen pulses. So I guess it follows that anytime it went rich you'd get an explosion there.

The metal cat has survived all this without a scratch.

[93_Clubman]

Good to hear you might have found the problem MB.