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Fuel Pump Voltage Issue

Simon-S14

By Simon-S14,
in Engines & Forced Induction

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Simon-S14 Grand Master

Simon-S14

Posted
Posted

Hoping someone can help me out with this one.

in my 32 i have a walbro which stopped supplying enough fuel for 240 rwkw, so a bosch motorsport pump was added inline (externally). Now i did the wiring mod to the walbro quite a while ago, ran a wire from the battery with a fuse to the back of the car, added a relay which was triggered by the original fuel pump wiring, and no worries. Now the new bosch pump gets its power from this wiring also. the prob that i have is that at idle the wire from the battery reads 12.5 ish volts (goes up to 13.5 with a blip of the throttle) where as the output of the relay reads 11.5 volts... so im losing 1 volt through the relay somehow. i changed the relay already and the story is the same.

have checked earth wires, using ohms meter and theres bugger all if nil resitance...

any suggestions?

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QWK32 Veteran

QWK32

Posted
Posted

i'm assuming you just spliced the bosch pumps power line onto the walbros source. one relay may not be big enough to let enough current through to power two pumps, so your getting a voltage drop. if you disconnect one of the pumps is the voltage drop still so big?

you may need to run two relays switched by the same signal, one for each pump. if that fails you may need to run a larger core wire or another feed from the battery for the two relays.

GeeTR Grand Master

GeeTR

Posted
Posted

Yah, sweet suggestions by QWK32. You can simply check the spec sheet or white paper for the relay your using (Google manufacture and model) for max current flow and (usually) max capacity for passing juice.

Interestingly, what thickness power cable are you running from batt to relay?

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