Exhaust backfire

[JIMYU]

My exhaust loves to give off a rather loud backfire quite often (it sounds mean and keeps me amused making people in London think there's gunfire )

I've always believed the cause of this to be unburnt fuel igniting in the exhaust....however my car mainly does it when its cold and the traction controll is on.

I can pretty much make it do it in the mornings by letting the TC kick-in then letting off the accelerator.

Can anyone tell me why, because surely the exhaust isn't hot enough to ignite any fuel..???

 

[Myki da Pyki]

It could be down to the dump valve not performing properly as that can cause backfire or its just the way the baffles are in the backbox

 

[JIMYU]

It won't backfire with the TC off though, I can't see how this makes a difference to the DV?

Exhaust is BF turbo back with 100 cell if that helps.

 

[Myki da Pyki]

In my manual for my dv it mentions that if not performing properly it may backfire. Hasnt TC got something to do with the N75 valve aswel?

 

[ttothec]

u prob wanna get that checked as the backfiring could ruin ur cat.

the previous owner of my car drove my car with a duff coil pack for a while and it ruined the cat (made it all collapse and get blocked)... the car would only boost to 4psi and obviously there was a huge drpop in performance

 

[Smoki333]

I've had mine do it once when i was in a rush, choke was still out trying to warm the car, put my foot down in first, wheels began to spin up, TC kicked in so i backed off quickly then POP, so quick change to 2nd foot down, spun up, TC kicked i backed off quick, POP

This was only pulling away hard to 2.5k ish rpm and backing off sharply,
So i know its the turbo fuelling more then suddenly been cut off and the fuel exiting the exhaust.

But i thought/Know the exhaust is meant to be rather hot to back it pop, So im kinda baffled too

Thats was in a rush mind, i normally let it warm up before letting the turbo kick in so im not doing it anymore to findout, i know it does it.

You can make them pop on command on a warm engine obviously and hot exhaust, by doing the same as above and backing off sharply between 2-3k where the turbo is just about to deliver boost, you just need to find its sweet spot ;-)

 

[loopydoo2002]

Ive got the same system as you mate and mine does the same thing, it sounds amazing when ripping away from a set of lights.

Ive always thought that the car is boosting up and then the TC kicks in killing the power all of a sudden so dumps the air normally but probably has a shed load of fuel left overs so that goes out the exhaust.

 

[SEATCOOBER]

mines the same even more know i have put a 3" bf downpipe on then the rest is 2.5 supersprint, lol did it today there was two pops when i passed this hooded chav, you should have seen him duck for cover, but any how i thought this was normal!!!!

 

[Ninja]

Mine pops like anything but only when cold...

I wasnt happy about it but last week a mate jumped in my car from cold and started revving it up.. Was popping like anything for a minute until i shouted at him!!

When car is warm and revved like that it doesnt do it though Only recently changed all coilpacks too so cant be that!

 

[ttothec]

are we talking about a "pop" sound or a backfire "BANG"??

i thought that when u said people mistake it for gun fire, u meant it was a loud BANG noise

my car pops all the time... thats pretty normal... its backfiring that would be a concern

 

[GlanzaV]

My thoughts would be:

Cold car so the car will be running a cold start map? Running more Fuel? (Don't know if this is the same for VAG cars)

I also assume our traction control works by reducing power, not applying brakes like other systems? So would it retard the ignition to do this? This will send a load of unburnth fuel through the exhaust, which will probably be enough to pop and bang.

That sound plausable to me? Mine does it now and again when cold too, I'm not generally spinning the wheels.

 

[JIMYU]

are we talking about a "pop" sound or a backfire "BANG"??

i thought that when u said people mistake it for gun fire, u meant it was a loud BANG noise

my car pops all the time... thats pretty normal... its backfiring that would be a concern

I'm talking about a loud bang...

I don't understand how a ice cold exhaust can ignite fuel...?

 

[jivejester]

Mixture is rich under load, and decel. Hits the hot cat and ignites the rich gasses, casuing the bang.

Same goes for cold starts, mixture is rich, also this time of year the air is colder and therfore more dense. This means more o2 in the combustion process, making the gas even easier to ignite.

 

[GlanzaV]

I don't understand how a ice cold exhaust can ignite fuel

You exhaust gas is always hot! around 850deg pre-cat and anything up to 750deg post cat... as soon as you turn the key! It doesn't take long for your exhaust to get warm believe me!

Couple this with the extra fuel and, if I'm right with the traction control retarding ignition, extra extra fuel... popping and banging will happen.

 

[loopydoo2002]

I'm talking about a loud bang...

I don't understand how a ice cold exhaust can ignite fuel...?

I was going to say, if you think you exhaust is ice cold try putting your hand on the cat. I bet u wont do it again, any exhaust gets hot quick but especially theses ibizas.