Bosch Motronic - Component Datasheet

Fuel Pump (G6) and Fuel Pump Relay (J17)

The fuel pump is of the high performance roller vane type that is located inside the fuel tank. Its operation is controlled by the fuel pump relay (J17) which resides in position 10 of the main fusebox in the 3B Coupe. Furthermore, the 12V feed to the fuel pump is protected by a 10A fuse at position S13 in the same fusebox.

J17 actually switches 12V power for many devices in the engine by means of its dual output pins 87 and 87a. These other devices are N71, N75, N80, Z19 and all of the fuel injectors. Checkout the schematics for more information. 

The decision to trigger J17 into the ON position is made by the ECU when engine speed exceeds about 25rpm. This is done for safety reasons so that the fuel pump is shut off in any accident that is heavy enough to stop the engine.

The trigger signal from the ECU to J17 is nothing more elaborate than a pin (#3) on the ECU (same pin on 3B and ABY) which is switched to ground in order to activate the fuel pump relay. 

The flow rate of fuel from the pump is proportional to the voltage applied to the pump terminals. This is important to remember when testing. Some indicative flow numbers are provided below... I'll add a voltage/flow graph that I have from the OFRM on file.

Voltage at pump terminals :

8V => Approx 1.2 litres per minute

10V => Approx 1.9 litres per minute

12V => Approx 2.6 litres per minute

14V => Approx 3.4 litres per minute

Note the RS2 fuel pump provides higher fuel flow - more info on that and other fuel pumps suitable for modified performance will be linked here in due course.

The part numbers below are for S2 Coupe only. The Avant and Sedan may use a different fuel pump due to differences in fuel tank design.