When an engine is going down hill and is being asked to work against the hill, why does it get so noisy in the exhaust?
There is no fuel or air going into the engine for combustion noise, so the pistons are simply moving up and down. Why the exhaust cackle? I've wondered this for a long time on my bikes cars trucks etc.
Why do you say there is no fuel or air going in? The valvetrain still moves and fuel is still drawn.
Most (not all) fuel injected vehicles will reduce the fuel in that situation (DFCO), but not completely stop fuelling.
