Fuel Pump Cutoff vs Turning Ignition Off

[ChewChewTrain]

Hi.

I've been turning off my ignition to save fuel by coasting (pulse and go).

Would I gain anything by installing/using a fuel pump electrical cutoff switch?

Thanks,
Doug
Oakland, CA

PS - Recently got 54.65mpg driving back from Los Angeles with my 1989 Civic hatchback.

[Ecky]

Using the ignition method may cause unburnt fuel to pass along to your catalytic converter, and may reduce its lifespan. However, cutting power to the pump will result in a slower kill, because fuel rail pressure doesn't drop to zero instantly. It may take a few seconds for your engine to die, and in those seconds it will probably lean out significantly.

I'm currently using an injector kill.

EDIT: Aerodynamics seems an odd section for this question.

[ChewChewTrain]

Originally Posted by Ecky

Using the ignition method may cause unburnt fuel to pass along to your catalytic converter, and may reduce its lifespan. However, cutting power to the pump will result in a slower kill, because fuel rail pressure doesn't drop to zero instantly. It may take a few seconds for your engine to die, and in those seconds it will probably lean out significantly.

I'm currently using an injector kill.

EDIT: Aerodynamics seems an odd section for this question.

Yeah. It was only after I launched the message did I see that it was posting to the wrong category.

My '89 Civic has fuel injection. Might you be saying that, with my ignition off, if my manual transmission is still in gear (such as going down hill), that the engine off, compression will still suck fuel into the engine / catalytic?

Thanks for the response, Ecky!

[Ecky]

Not exactly. As I understand it, it's more that after you cut spark, the engine will still inject a few squirts of fuel before fully coming to a stop. I don't anticipate major problems with any of these kill methods though.