97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

I'm not getting 12 volts (measured at the starter lug) to the fuel pump during the start cycle. If I bypass the low pressure sensor, the pump will start pumping fuel, so my problem is in the starting circuit... how many volts should I see coming off the starter and where to the two purple-yellow wires meet? (one cones from the stater and the other from the oil pressure sensor)... I wonder if I have a bad connection, that's causing the voltage drain.

It's either that or

1) weak starter that's drawing to much current to start the motor, so nothing is left for the fuel pump
2) bad fuel pump, but it runs like a champ on 12 volts
3) the oil pressure sensor, but that shouldn't impact the start cycle, right?

Thanks!

Re: 97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

Very common for the terminals on the switch to corrode and lose the circuit. Try pulling the wires off the switch and joining them together. If that fixes the problem, get a new switch.....

Chris........

Re: 97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

By switch, do you mean the low pressure sensor that supplies power to the fuel pump? Would that impact the starting circuit... it pumps fine when the oil pressure is up (engine running).

Thanks!!!

Re: 97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

Bad connections are a common problem on the terminals on the oil pressure switch, but if you aren't getting any voltage out of the purple yellow wire terminal on the starter, then you have a bad starter solenoid.

Re: 97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

I get power from the solenoid, but it drops to 6-8 volts while cranking, making me think that the starter might be bad (drawing too much current)

Re: 97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

kmmn said:

I get power from the solenoid, but it drops to 6-8 volts while cranking, making me think that the starter might be bad (drawing too much current)

Click to expand...

Could also be faulty battery connections or a low battery. It shouldn't drop below 10V while cranking.

Re: 97 Mercruiser 4.3 (2bbl) Fuel Pump Wiring

The battery is fully charged (one year old and it did the same thing when the battery was brand new) and it does crank fast. If this was a car, I'd crawl under it and swap out the starter and not even think about it, but that's far more of a pain in the butt with an I/O.