Purpose of EEC-IV Pin 8

[DPDISXR4Ti]

Can someone tell me what the purpose of the pin 8 circuit is that goes to the Fuel Pump relay on the same circuit as the inertia switch? Is it an input or an output? It's not found at all on the Euro Fords (Merkurs) of the same era that I'm more familiar with.

 

[pjtoledo]

fuel pump monitor. input to the computer.
I found that info in a couple Taurus manuals, 92 & 95. it's not used on some models/options.

 

[DPDISXR4Ti]

fuel pump monitor. input to the computer.

Thanks. I found this which describes in more technical detail how it works. As best I can determine, it doesn't effect any running changes, it's just used for diagnostic purposes.

Yes it is a bias voltage, internal to the engine computer the fuel pump monitor line is supplied with battery voltage which passes through a high value resistor ( thousands of ohms) before it reaches the outside of the engine computer. The internal resistor inside the engine computer is roughly equal to the resistance of the inertia switch LED warning light. This why your meter shows roughly 1/2 battery voltage with the inertia switch tripped.

By reading the voltage at this point the engine computer can work out if there is a supply circuit failure (for example fuse or relay) or a short to ground or the inertia switch has tripped .

A way to make sense of this is to work out or test what voltage shows on the FP monitoring wire in normal running and when all the possible fault conditions occur and note these down to make a table. The fancy name for this is a Truth Table.

 

[DPDISXR4Ti]

I question why Ford bothered with this. All it's really monitoring is whether 12V got to the fuel pump. Obviously it can't measure fuel pressure. It can't even verify if the pump is working. I guess it could tell you if a wire or the fuel pump relay failed.