Fuel pump voltage?

[mercrazy]

What should pump voltage be on 225 promax? At idle it’s only 10 volts. It goes up to 12 at higher idle. New Battery has consistent 12.8 volts with engine off.
Engine seems to have intermittent problem running pump. Engine would start but struggle to run and wasn’t getting gas. I tried to spread the pins on ecu plug but some were impossible. After reattaching, it ran ok but I don’t have confidence in it. Is the low voltage at pump normal? Could the harness have a broken wire making intermittent connection?

[Jim Speros]

In absence of any other response. It does not have to be 12 volts especially at idle. The ECU in some cases varies voltage to pump.

[David - WI]

You can try putting dielectric grease on the harness pins to improve the connections.

[mercrazy]

You can try putting dielectric grease on the harness pins to improve the connections.

When I connect meter ground to block and measure hot side of pump, it shows same as battery voltage. When I measure across both pump connections is when it’s low. Could the ecu grounding circuit be going bad like you hear about so much? I tried to spread the pins on ecu connector and it seems everything is working right now but voltage is still low at idle.
When the ecu ground goes bad, is it safe to power the pump straight off the purple wire or should I use a relay?

[KeninSC]

You should use a relay and not power straight from the Purple wire if you bypass the ECU.

[mercrazy]

You should use a relay and not power straight from the Purple wire if you bypass the ECU.

The red wire to pump is not that big. How much current does pump draw? I’ve known people to run straight off the purple wire.

[KeninSC]

I'm not real familiar with the Promax pump but that is a 39lb system isn't it? The Bosch pumps on the 260's and 280's can draw 11-12 amps.

[skialot2]

What should pump voltage be on 225 promax? At idle it’s only 10 volts. It goes up to 12 at higher idle. New Battery has consistent 12.8 volts with engine off.
Engine seems to have intermittent problem running pump. Engine would start but struggle to run and wasn’t getting gas. I tried to spread the pins on ecu plug but some were impossible. After reattaching, it ran ok but I don’t have confidence in it. Is the low voltage at pump normal? Could the harness have a broken wire making intermittent connection?

That is the way it is supposed to be. The ECM controls the ground for the fuel pump. Not the positive. But it never make it a complete ground. From the manual:

[JCSmile]

If you are looking to leave the motor mostly stock I don't think there is any problem running through the ECU. That being said, ive had 3-4 merc ecus lose their fuel pump circuitry. 10amps is a lot to flow through the ECU for 30 years. I use purple wire to run a relay and power a Bosch pump direct to the battery with inline fusing.

[David - WI]

Also, measuring voltage across the wires to the pump is not really a test of anything... it's kind of a half-assed voltage drop test for the pump itself, but not really.