Subaru in all of their technical literature refer to the control module as a modulator for a very good reason. The pump is in fact pulse width modulated as I stated way back in post No 8 detailing how the pump control system works.
It is now being asserted that I was and am wrong. Five minutes with Google has quickly turned up confirmation that at 89.75 yrs I am far from senile. The system presented does not include a resistor but the identical principle involved is clearly stated and is exactly similar.
Go here and Scroll down to the heading “Fuel Pump Driver Module” and read about pulse width modulation:-
https://www.autoserviceprofessional....sis-and-repair
I repeat what I have previously posted in an effort to get the thread back on track.
Thread 8 :-
The pump receives its negative supply via two alternatives, i.e. the resistor R34 or the fuel pump modulator switching transistors which are controlled via the ECU.
The resistor will provide a reduced voltage and therefore limited pump speed in the event of the pump modulator or its control failing. The resistor will also prevent full zero voltage in respect of pulse width modulation speed control of the pump. (An innovation also used by Subaru in respect of the control of transmission pressure.)
Under normal circumstances pump speed and therefore pressure, will be controlled via the modulator and ultimately by the ECU
by means of pulse width modulation.
Thread 19:-
(1) “When I got the engine running normal, I would unplug the fuel control module from under the deck lid, yet the car would continue to run normally.”
Therefore the resistor is completing the pump ground circuit.
(2) “Yet when I unplug it (The resistor), the car starts. When its plugged in it does not.”
Therefore when the only the modulator is in circuit and the pump is running at a controlled speed and pressure the car starts, but when the resistor is connected in parallel with the modulator it does not start, possibly due to high pump speed and abnormal fuel pressure.
The final power transistor in the modulator is NPN and is switching on when the driver PNP is switched on via the ECU at c14. The ECU ground switching circuit must be OK as the pump relay is operating OK.
Conclusion:-
A short to ground within the resistor housing would result in the pump always running at full speed and this would account for the strange situation as per (1), the failure to start as per (2) and also other erratic engine behaviour. Furthermore the pump must draw a lot more current than one would expect.
Alternatively, both resistors measured are faulty and have reduced in value, which would be extremely unusual and unlikely but not impossible. Unfortunately the correct specifications can not be located. Check the resistor for an internal short to ground.
Post 10.0 included:- I would expect the resistor value to be in
two figures but it can it not be estimated without full details covering the pump motor and its requirements.
"The photo now posted appears to show."
The resistor is marked A1,5 000R20 which means that its correct resistance is 20. ohms. The six digits allow for figures in K ohms.
QED.