What causes backfiring?

[Slant]

and is it harmful to the car?

[autxr]

Excess fuel igniting in the exhaust.

Bad for the car...

It depends on how severe, but generally, yes.

My old Celica ('78) had a backfiring problem, and I would screw around making it backfire. Eventually (after about a week) it ripped a hole in the muffler.

That same pressure from a back fire could theoretically enter the combustion chambers as well.

A little popping isn't a big deal, but if folks duck for cover and think they are under attack, it is safe to assume it isn't helping the car any.

Even worse, you can get a back-fire through the intake (never heard of it witha fuel injected car, just carbed). In that case burning fuel would be ejected out the intake and pretty well burn things up.

Scott

[Slant]

"Excess fuel igniting in the exhaust"

Can you describe this a little further?

[tool462]

When the fuel is ignited in the piston chamber, some of it goes unburned and gets sent through the exhaust system. If your car is REALLY inefficient (usually as a car ages it gets worse) it'll send enough fuel out into the exhaust that it'll explode when it gets to the cat or muffler, because they are very hot.

[autxr]

For combustion you need fuel and air. And, an ignition source.

The engine supplies the fuel (and often the air), or the air can come in through the tail pipe. The "excess" part means that you are running rich. Lets say you are cruising along at wide open throttle and you lift off the gas.

The butterfly valve in the throttle body closes (no there is no air), then the injector lags and fires. No air in the engine but there is gas. So, most of that gas enters the tail pipe. If there is enough air present at that point and an ignition source then boom.

Well, there is back pressure in the exhaust system (the muffler chambers in particular. So, what happends when air expands rapidly in a closed system then escapes?

Bang.

Scott

[aZnTrD2k]

so how do we avoid it then.........

[autxr]

Tune the car properly.

Are you having a problem with backfires?
A little burbling is normal if you run a straight exhaust. A real backfire will get the cops called. Small pops aren't a big deal either. If it sounds like a shotgun blast, then you have a problem.

Scott

[t2000gts]

can backfires be caused from a misfire?

i heard people use misfiring systems to tune turbos. how does this work? and does this cause backfiring? good or bad?

[Kit99bar]

so when those FnF cars where spitting flames out
was it back firing?

[Maelfyn]

Well it was.. but it was fake