Fuel pump control unit AKA Revolution sensor

[zstalker]

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!

~Erik

[coxy]

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.

 

http://www.ultimatesubaru.org/forum/topic/143962-85-brat-quit-not-starting/

[Gloyale]

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 February 2, 2014 by Gloyale

[czny]

Here ya go, Chevy Vega oil pressure switch:

http://www.ebay.com/itm/Standard-Motor-Products-PS64-Oil-Pressure-Sender-or-Switch-For-Light-/141086607398?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AChevrolet|Model%3AVega&hash=item20d96ac826&vxp=mtr

 

There's also these Hobbs switches:

http://www.ebay.com/itm/Three-3-New-Hobbs-Pressure-Switches-76575-4-also-Replaces-M4006-4-Switch-/230736088050?pt=BI_Heavy_Equipment_Parts&hash=item35b8f14bf2

Edited February 2, 2014 by czny

[ajslacker]

Just in case anyone is having the same problem I did what Gloyale said jumping the wires for the fuel pump control unit and it didn't work. But I did notice on my fuel pump it's a blue and red wire not a blue and black one and it worked when I did blue and red to the main 12 volt black wire. it might be different for different vehicles but for my 85 brat it was the blue and red wire and the larger black wire the 12 volt one I just put a tiny little wire and jump the two in the connector.

[skishop69]

You need the controller for safety reasons. Never hot wire a fuel pump. In an accident, it won't shut down and could lead to someones death and possibly a lawsuit to boot. If you can't afford to replace it, try this.http://www.revolutionelectronics.com/Fuel_Pump.html  I use these when I do restorations. Just finishing a frame up restoration on a 68 Mustang and it got one. Works perfectly.

[GeneralDisorder]

Or you could go even cheaper and get an oil pressure cut-out switch. 

As for troubleshooting - those rev sensors take power, ground, and a tach signal. And they output power for the fuel pump and some also power the choke. The wiring is pretty simple and easily figured out from wire colors and sizes - tach signal is going to be small and yellow, power supply and fuel pump are going to be larger and one will be ignition switched hot, the other will show a low resistance through the pump windings. Ground will likely be black. Start by checking for the tach pulse at the unit, and check for power and ground of course. Test light will do the job. Ultimately if you jump power to the pump it should run, and if you have power, ground, and tach signal present then the FPCU is bad. It's pretty much that simple. 

GD

[Crazyeights]

Another option is the fuel pump inertia (or impact) switch used on older 90's Ford products. They almost never fail so the junkyards are full of them for cheap. Grab the connector with it. It is a simple 2 wire hook up.

[subratco]

On 7/16/2018 at 7:19 PM, Crazyeights said:

Another option is the fuel pump inertia (or impact) switch used on older 90's Ford products. They almost never fail so the junkyards are full of them for cheap. Grab the connector with it. It is a simple 2 wire hook up.

Which wires did you connect to?