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Fuel pump control unit AKA Revolution sensor

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1984 GL-10 Hardtop Coupe FWD.  EA81, Carter/Weber carburetor.

Fuel pump isn't operating.  If I provide fuel down the carburetor the engine will run properly until I stop fueling.  Replaced fuel pump, and distributor (to provide proper ignition signal, the shaft had some play).  I'm focusing on the Fuel Pump Control Unit (FPCU), but I'm not in a position where I can afford to experiments with a $150 new one without being fully convinced that it will remedy my situation.  I need actual diagnostic information about this box specifically.

Does anyone know the actual function of the FPCU?  First off I'm a Subaru dealership technician, so I'm certainly not shooting blind, but I can't find any actual information about the operation of the FPCU.  Using the factory service manual, Haynes, and Chiltons manuals I've been able to find almost nothing of what kind of output this module produces.  The manuals all basically say " if power and ground are there, tach signal is coming in, then the pump will run."  Yes, that's wonderful, but run how?  From what I've figured the pump produces a pulsing power signal, since the pump does nothing and blows the breaker in the Powerprobe after a moment when I supply power and ground directly to the pump.  A replacement pump (new) had the same result leading me to believe the pump needs a on-off pulsing power source to operate the plunger solenoid.

Followup question:

Has anyone ever found a way to bypass the FPCU?  if it were as easy as a switch or a relay to provide bypassed power to the pump I would have done that, but that was not successful.  Can any of the components inside the FPCU be replaced (resistors, capacitors, etc).

I implore you USMB and your fountain of knowledge!


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See this topic the FPCU seems simple enough just resistors a ceramic one as well (White long rectangular part) plus capacitors and a circuit board type actual relay that will have points in it, Nothing that cannot be repaired after a trip to an electronics supply house and some time with a soldering iron.



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You can bypass it by Jumpering the swithed 12v(B/W) into the unit over to the pump power wire(Blue/black).


This will run the pump with Key on......but will not provide shot off protection for a no-run situation like accident or fuel line burst.


There are a few different FPCU's out there......you need one from the correct EA81 model(same engine/trans/carb)....(not the EA82 ones and not the feedback ECU/Carb ones)


The pumps do not need anythign but regular 12v+ and a ground.  The pulsing is just to trigger the coil of the FPCU closed to complete the circuit.  If your pump isn't working or blowing fuses with straight power then something is wrong.


Lots of people just wire the fuel pump to a switch. 


I've once seen a GM 3prong oil pressure switch installed and the power for the fuel pump run through it so FP only operates when there is oil pressure.  Another good option.

Edited by Gloyale

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