Switch key off for engine braking?

[JimmyC]

When I am going down a hill using the engine for braking I often turn the key off. The best I can tell this shuts off the flow to the idle jets and stops all backfiring and smelly exhaust due to reversion. Is there any reason I should not do this?

[Hugues]

Interesting. I never tried but was thinking about a way to shut off the idle solenoids when engine breaking. Switching the key off also turns off your lights,...
You're engine is backfiring when engine braking? I never noticed that on mine. Maybe a combination of too rich mixture and too late firing?
I have added a Megasquirt 3 Pro Mini ECU to my Pinz now and monitoring engine rpm, air-fuel ratio, vacuum, temperature,.. One thing I noticed is my mixture is too rich while engine braking, although mixture is OK at idle. I'll soon switch to ECU to control my advance.
I'm thinking to use my ECU to switch off my idle solenoids when engine braking. That would be done automatically based on engine sensors.

[rmel]

I assume what you are describing is post ignition not back firing -- Exhaust "farts"

That can be caused by a very lean condition. Lean under a high vacuum requires more advance
as the fuel burns much slower under that condition then results in unburnt fuel in the exhaust.

Why this happens is; your going down a step grade, the engine RPM is being forced higher than
the fuel being added,a high vacuum condition and very lean, advance is insufficient thus post firing.

You could try making your idle richer to help reduce this somewhat. Hard to eliminate totally.
Some electronic ignitions have a MAP sensor so you could in principle just increase the advance
further when the MAP value is much higher than the MAP at idle.