MFI Relay - What's it for?

[Rslevin]

I have an MFI relay that has lose parts, but I wonder what it is for? The MFI pump has no electrical connections. What is the relay's purpose? And how does a failed unit manifest itself in symptoms? Thanks, Rich

[Flieger]

It energizes the solenoid (one of the solenoids if you have a 1969 pump) which pushes the rack past idle fuel delivery volume and effectively stops fuel from going into the motor. The box controls when this happens- which is when the engine is above a certain rpm and you close the throttle -i.e. engine braking. The box increases engine braking, reduces fuel consumption slightly, and stops backfires on overrun (though you need to come off the throttle abruptly to get the microswich to close).

Here is a thread that has everything you need to know to fix it yourself: For MFI Gurus. . .and friends of Warren . . .

[Rslevin]

Thanks, that was very helpful. Regards, Rich