Manual Fuel pump switch, and tips Options

[ONTHEGRIND]

so I am installing a new bosch fuel pump for my factory fuel injection system.. Where my factory fuel pump used to one in the stock location, one of the mounting tabs is gone from a little bit of rust, so I am moving it to the firewall. And mounting it with sheet metal screws.. Any body have a manual fuel pump switch wired up so if that relay crap decides not to work I can just flip it on with a switch.. where do you have it mounted and how do you have it wired up ?

Thanks

[ONTHEGRIND]

I put a wire from tb4 to a ground when I put it in the plug in the lower left nothing happens when I turn the ignition to the on pos. I hear a click from the relays.. I toched a wire to the top connectors on tb4 and got sparks

[bperry]

I put a wire from tb4 to a ground when I put it in the plug in the lower left nothing happens when I turn the ignition to the on pos. I hear a click from the relays.. I toched a wire to the top connectors on tb4 and got sparks

Man those relay board photos I did sure are getting around a lot lately.

Yes be very careful here. You can melt wires if you are not careful.

The pins on t4b are numbered:

III I
IV II

With Pin III being in the upper left corner, closest to the drivers side front wheel.
This is the pin that needs to be grounded to get the fuel pump relay to click down
to turn on power to the fuel pump.
See the technical article for a close up photo of the pin that needs to grounded:
FuelPump for carbs

Pin I supplies +12v from the power supply relay. When the power supply relay
is energized (anytime ignition key is turned on) it is a direct connection with no
fuse to +12 on the battery. Short that to ground for very long and you will melt
wires.

Pin II and IV are tied together and are +12v while cranking the starter.
It is directly tied to the line that feeds the solenoid.
The FI brain uses this signal to know you are trying to start the car and turns on
the fuel pump by grounding Pin III.
Ground this pin and you have a dead short through the ignition key while you
are trying to start the car. This could also melt wires as there is no fuse in
this path.

Pin III
The FI brain grounds this pin when the starter is running -OR- only when
it "sees" the engine running. The FI brain monitors the distributor coil to detect if
the engine is running.

The reason that the fuel pump shuts down after a few seconds if you don't start
the car is that the FI brain isn't seeing the engine running (distributor driving the coil)
or the starter cranking.

So in order get the FI enabling the pump it not only has to be able to ground
pin III, but it also has to see the coil being driven.
If the FI brain thinks the engine has died, it shuts down the fuel pump by
ungrounding pin III.

So the ground trick for pin III when using FI is only for testing to see
if the fuel pump will run. I'm pretty sure you can't run the car this way.
I believe the FI brain needs the power that comes from pin I.

A big clue is when things are plugged in as normal.
(Connector from FI brain is plugged into t4b)
Does the fuel pump run then stop when you turn the key to "run"?
If so the relay board and the fuel pump relay is working fine.
Then, if no start, it may be due to the FI brain not seeing the distributor
turning.

Check the wires around the coil, there should be a wire that feeds
into the FI unit. Perhaps it is loose, broken or dirty.
I can't remember the wire colors off hand for that.
Perhaps someone else will chime in.

--- bill

[Spoke]

Pin II and IV are tied together and are +12v while cranking the starter.
It is directly tied to the line that feeds the solenoid.
The FI brain uses this signal to know you are trying to start the car and turns on
the fuel pump by grounding Pin III.

In addition, when starting the car, the FI brain will widen the injector pulses to get more fuel into the cylinders to help the car start.

Nice write up Bill.