Start 9/9/2022.

• Don has a spare relay on hand
• Replacement pump costs $9000

Two DC electric boost pumps provide the engines with a standby fuel feed system. They are available for engine starting, and as a backup fuel feed source if either main ejector pump output pressure is too low to satisfactorily feed its respective engine. The left boost pump is powered by the DC battery bus, and the right boost pump by DC bus 2. The boost pumps are located downstream of their respective collector tanks, on the fuel feed lines to the engine-driven pumps. During normal operation, the only pilot action required is to arm both BOOST PUMP switches on the FUEL control panel prior to engine start, and disarm them after shutdown.

When both BOOST PUMP switches are armed, the boost pumps are activated if low pressure is sensed at either left or right main ejector pressure switch (this is the case prior to engine start).

If a single BOOST PUMP switch is armed, both boost pumps will be activated if low pressure is sensed on the armed side’s main ejector pressure switch. For example, if only the left BOOST PUMP switch is armed (pressed in), then both pumps will activate if low pressure is sensed at the left main ejector output. The boost pumps can provide fuel to both engines fuel feed systems through a crossover feed line.

If a boost pump has been activated, sufficient pump output pressure is indicated by the green ON legend in the switch/light. Insufficient output pressure is indicated by the amber INOP legend, and the L (R) FUEL PUMP caution EICAS message.

• Check pump grounds
• I'm 80% sure that the problem is the RH Boost Pump Switch, between contacts CC and CNO.

If it were the relay, then the failure would be just as likely to occur when the RH or LH switch is down.

You didn't explain what happens if you push both LH and RH boost pump switches in. I'm thinking that all of your problems go away.

The CNO contact on the boost pump switch is directly connected to the relay coil. When you energize and de-energize a circuit with a coil like that, it makes an inductive spark. Usually, they place a diode in parallel to block such sparks. The diode shown is not connected in parallel.

I can test to see if I am right be measure with my voltmeter between CC and CNO. It should always measure zero volts if the contact is good. But if a higher value shows up, that means that the volts from the circuit break is not making it to the relay.

I don't know how hard it is to get to the back of that switch so I can measure.

• A - L (R) P Switch = MAIN EJECTOR FAIL (Status MSG)
• B - L (R) P Switch = FUEL PUMP (Abnormal MSG)
• C - L (R) DeltaP Switch = SCAV EJECTOR (Abnormal MSG)
• D - L (R) T Switch = FUEL LO TEMP (Abnormal MSG)
• E - L (R) P Switch = FUEL FILTER (Abnormal MSG)
• F - (L) T Switch = BULK FUEL TEMP (Abnormal MSG)
• G - L (R) FUEL XFLOW SOV OPEN (Abnormal MSG)
• H - Engine-Driven Pump

Fuel Distribution Electrical Schematic

• LH Switch IN-OP, RH Switch pump Light On. Push LH Switch, LH Light On - Good, task msg. gone

• LH lights off, RH light IN-OP, Engage RH Switch On, after 1 second RH pump light On, after 3 more seconds, LH light IN-OP

• LH IN-OP light On, RH pump light On, RH Switch In, LH Switch Out, (not pictured: LH boost pump was on then after 15 seconds LH IN-OP light On, waiting for LH boost pump to come on (it didn't))

• After 75 seconds, RH Pump Light On, LH Pump Light On, RW Switch In, LH Switch Out, Msg Removed

• LH IN-OP Light On, RH IN-OP Light On, Push LH Switch In, both IN-OP lights go Out, both pump lights go On - "Operation Normal"

• LH IN-OP Light On, RH IN-OP Light On, Push RH Switch In, (RH IN-OP light stays On) LH IN-OP light goes Out, after 1 second LH pump light On, RH Fuel Pump task msg.

• LH IN-OP Light On, RH IN-OP Light On, Push LH Switch In, after 1 second both pump lights go On - "Operation Normal". Then Don pushed LH Switch Off, after 3 seconds - beep beep, both IN-OP lights go On

• LH IN-OP Light On, RH IN-OP Light On, Push RH Switch In, after 1 second LH pump light On In, after 3 more seconds, RH pump IN-OP light On, then RH pump IN-OP task msg.

• LH IN-OP Light On, RH IN-OP Light On, Push RH Switch In, both IN-OP lights go Out, both pump lights go On - "Operation Normal" this time

• LH IN-OP Light On, RH IN-OP Light On, Push LH Switch In, both IN-OP lights go Out, both pump lights go On - "Operation Normal"