Intermittent loss of 12v to High Pressure Fuel Pump

[badcrabs]

I have a 1999 Yamaha SX200TXRX that has been losing power to the positive only terminal on the high pressure pump (checked with my DVM). Sometimes it acts up right at startup when dead cold and other times I am at plane or high rpm and it completely dies. I have rigged up a wire with alligator clips on each end to "hot wire" the positive terminal of the fuel pump and it then runs fine and will run all day.

I don't like rigging it this way and am trying to figure out if its the pump, ECU, wiring harness or a relay of some kind. I don't want to just start swapping $1000 parts (fuel pump, ECU) to figure this out.

I know the system operates by supplying or taking away ground .. not the positive 12v. I read some previous threads about a pump drawing too much amperage and the ECU shutting the pump down but again that would show up with ground missing not 12v + . I also saw a thread about a resistor above the injector rail that the voltage should flow through below 1800 rpm.

Given that sometimes it runs fine, sometimes not at all (it cranks but no voltage to the high pressure pump) and sometimes runs great and then suddenly dies but will run with a "hot wired" patch around leaves me wondering where the heck to start.

Any help or guidance is greatly appreciated,

badcrabs

[rodbolt17]

I would start with the main relay,fuses and wireing harness.
Voltage does NOT flow.
the ECU selects the pump ground path.
below about 1200 RPM the path is via the resistor, above 1200 its striaght to ground.

[jb123]

i recently had the same issue,tho losing ground, after replacing HP pump filter, Rodbolt suggested checking/cleaning pres reg filter, on top of vst, mine was dirty but i still had issues, ended up also being dirty injector filters
my HP pump amps were 5.2, on the hi side which he stated would cause ecu errors
luckily i have twins to swap parts to isolate issues

[badcrabs]

Intermittent loss of 12v to High Pressure Fuel Pump

Update .. took the boat most of day yesterday and it had the same issues at startup. I needed to keep my "hot wire" patch on to keep it running. If I disconnect the alligator clip that runs to my 12v buss panel the engine runs for a few seconds then dies and won't start without me reconnecting it.

Once I got it back to the dock I tested it again by removing the workaround 12v patch wire and it ran without it being connected! Like I said .. intermittent .. the worst kind of problem to have.

I will check the relay, fuses and harness like you suggested. Thanks for the replies.

[99yam40]

sounds like a bad connection, seems it would be easy to find by checking where you have the 12volts+ and where you do not when problems is happening