Please go back and read the several prior posts of others and myself. You said fuel usage increased. To be able to say fuel usage increased you have to be comparing the new level of usage to some prior level of usage. As others have noted there is an increase in rpm's when using engine braking but fuel usage is very low. It certainly doesn't increase over the usage you would encounter under normal driving conditions.
I think, from the reading ive done round this subject in the past, that the overrun cut-off is activated only when throttle is in idle position and revs are above a fixed amount. It doesnt seem to make any difference whether you change gear on a manual (certainly not on cars up to very recent years) so long as you maintain the revs above the fixed preset. If you let it drop below the level it fires back into idle duty cycle (sometimes slightly more to quickly replenish the fuel puddle in the port but we are only talkign about 30-40% extra for a split second).
No way.
The decel valve, O2 sensor, and IAC, and AAR, and e else, compensate, and lean the mix accordingly during deceleration. In extreme cases, fuel is cut off, and all you have is "engine braking". Still, it's hard on the engine to rev it, under load. The rods and journals don't care whether it's loading or unloading. It stresses the bearings.
Brake linings are cheap (but watch for fading). I used to coast down the San Bernardino Mountain roads, mainly Hwy 18 and 138, when low on petrol, by going on and off the brakes. Ride the brakes constantly, and you will be in trouble, due to =fading=. Yes, even with disc brakes, though not as severely as with Bendix brakes.
Not really. The venturi is closed off, if your foot is off the accelerator. The idle ports, below the throttle plates, are limited in size, and orifice size hits a hard limit above a certain pressure gradient. You will have a lean condition, due to the idle air bleeds running at max depression, anyway. But step on the gas pedal, and all bets are off.
Oddly enough: Flooring the accelerator pedal with the ignition OFF will provide even better engine braking, but, in a carbureted engine, it will waste much fuel, unburned, out the tailpipe.
In an EFI engine, it doesn't matter. The ECM knows what is going on, and pretty much cuts off fuel to the injectors during deceleration.
Interesting...
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