Flatulating automobiles

Factual Questions
1

As long as automotive stuff seems to be coming up:

When I was a kid, I remember a technique for making a car backfire like a shotgun blast. What you did was shut the ignition off while going downhill, letting it transmission brake for a few seconds (works better with a standard). Then, you turn the ignition back on, and KABLAM!

Not good for the vehicle, obviously, and I take absolutely no responsibility for any fool reading this who tries it and blows their exhaust system clean off.

My question - why doesn’t this seem to work on newer cars? Once or twice in recent decades, my mature adult status has somehow gotten overridden, I would remember this, and try it, suppressing fears that I would wind up buying a new catalytic converter for my foolishness. No backfire, or maybe just a little barely noticable “poot”. Perhaps a fitting analogy to most attempts to recapture the glories of ones youth …

Cars are a lot more complex, now, of course. What advance in automotive technology has prevented this bit of adolescent tom-foolery?

My leading guess right now would be fuel injection - when you shut off the ignition, do the fuel injectors stop injecting? Whereas vehicles with carburetors will continue to draw fuel mixture letting you build up unburned stuff in the manifold?

Inquiring, if juvenile, minds want to know.

2

One reason is fuel injection. With older carburetted cars, when you used engine braking, the engine vacuum would draw fuel and air mixture into the cylinders, and this unburned mixture would go into the exhaust. Then when the car was started again, the hot exhaust gases of combustion would ignite the unburned fuel-air mixture in the exhaust system.

With a fuel injected car, normally when you kill the ignition the injectors stop spraying fuel, and thus only air (and some very small amount of leftover fuel) is drawn into the exhaust.

3

Oh, I see at the end of your post you figured out the correct answer yourself. D’oh!

4

Thanks for the confirmation.