"Why doesn't pulling the fuel pump relay kill the pumps and cause the pressure to run down? Does this relay impact on spark also, hence the engine dies immediately?"

I haven't traced it out, Dave, but I believe the answer lies in the fact that it really is more than just a FuelPump relay, as everyone insists on calling it. Fuel Injection Relay is more accurate, especially since it controls power to the injectors among other things.

Loss of power to the FI system will stop the engine as quickly as loss of spark (no fuel injected = no combustion). The effect is the same even with K-jet's Continuous (non-electric) injectors, because the pressure quickly drops below what's required to open the injectors (about 45psi I think).

So the engine stops quickly and there is residual pressure in the system—just as there is after a normal shutdown.

That's my theory anyway.


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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.