BOOST PUMP?

[Another Distraction]

S/N is in my signature

What does this Optimax "boost" fuel pump do that's located in the vst tank? As a former HPDI owner I'm not used to this 3rd style pump called a boost pump.

If boost pump fails does motor 100% not run and leaves me drifting or does the diaphram pump cover for it and I limp home at 3 knots?

[DewRonInc]

One sends fuel to the high pressure pump, pulse pump just fills vst

[DewRonInc]

I changed mine with Walbro pumps, works great, mine sounded bad, noisy, now they are not

[Another Distraction]

Both pumps, boost and diaphram, send fuel to high pressure pump because there's only one fuel feed line going into VST. Are you saying fuel won't get to high pressure pump unless boost pump is working? Fuel wont flow through or around boost pump?

Maybe boost pump fills the high pressure pump with a lower pressurized fuel so high pressure pump isnt starting from zero psi?

[Another Distraction]

And when I turn key on and hear a fuel pump run for a few seconds, is that the boost, high pressure, or both running?

[DewRonInc]

Both,

[DewRonInc]

Think of it as a lift pump, boost pump is horizontal sends fuel to high pressure pump which is vertical, attaches directly to fuel line to rails

[JOE54]

diaphram fills chamber for boost to use to supply HP pump for inj useage , both run at key on and no is dead in water no limp

[Another Distraction]

I see how this works now and having 2 pumps is 2x more likely to be left drifting out to see. Darn.... I guess an extra VST assembly will be a good offshore spare part to carry.

[Savage]

I've owned Optimax motors since 1999 and never had a failed fuel pump. Carrying a spare VST is over the top IMHO.

[EuropeanAM]

Technically low pressure and high pressure, but the short of it is that the low pressure pump ensures a clean and constant supply of non-aerated fuel to the high pressure pump.

These pumps are quite durable, especially the versions that are immersed in fuel within the IVST (specifically 2003 and later 3L Optimax models). We see VERY few failures on these pumps.

[Another Distraction]

Non aerated, understood.

If low pressure pump fails then boat still crawls home?

I'm an ocean guy. After 25 miles out there's no tow service to come get me.

[EuropeanAM]

Provided that the VST remains full, you can usually keep the engine running at low RPM's (at least enough to putter home). Pretty rare occurence on that IVST Design, though.

[Another Distraction]

Cool, thanks.

[Trimguy]

I have an 05 225 opti and after it would warm up it it would start to rev then fall on its face and not rev over 1200 rpm. Turns out it was the vst was full of decayed fuel line and gunk. I took it somewhere and was diagnosed as high pressure fuel pump getting hot and failing so I bought the high pressure pump on way home and changed. When pulled vst that's when found how disgusting the vst was but changed pump anyways since i was in there. Runs strong now but i honestly think it was gunk stopping up one of the pumps causing the problem.....not the pump itself.

[Trimguy]

High and low pumps.....500 ea

[Another Distraction]

Agreed. There are some rubbers in the vst that are critical too so bad pumps alone aren't the only thing that cause VST issues. I'll tear mine down if I can find the time.

You had decayed fuel line past the big screw in filter and into the vst tank where the pumps are? I would think those fuel line parts are to big to get in there.

[DewRonInc]

Get a service manual, it will help a bunch, I replace everything in mine when I changed pumps, no big deal, but manual is key

[DewRonInc]

If line is questionable, replace all of it

[EuropeanAM]

You had decayed fuel line past the big screw in filter a into the vst tank where the pumps are? I would think those fuel line parts are to big to get in there.

That was very likely decayed FUEL (in order for line to get there, it would have to pass the filter, make it's way down the small passage front to back, and then pass through the NEEDLE/SEAT. Pretty rare unless something really unusual has occurred in servicing/repair.