Why are outboard fuel systems so complex?

[bigoilman]

I've been an automotive mechanic most of my life (I'm 54). Why are outboard fuel systems so complex? I've converted '30s hotrods to modern fuel injected motors, even my '77 dually is turbo LS powered. The fuel systems are easy. One in-tank pump of whatever size your combo requires, one inline filter, a fuel pressure regulator and either a dead-headed system or a fuel return line to the tank.

My old Optimax has 3 pumps. I just read that a new 425 Yamaha XTO has 5 fuel pumps! Why? 5 more points of failure or in the case of my buddy's 42 Yellowfin, 15 points of failure where 3 would've sufficed.

I don't get it. Enlighten me.

[Savage]

Have to go to the Yamaha boards to explain the 5 pumps. We only deal with a maximum of THREE fuel pumps on these boards......pretty simple.

[bigoilman]

It was just an example. I don't see a need for any EFI motor to need more than one pump and ZERO actually on the motor, they should be in the tank and ANY tank can be retrofitted for EFI if that's the issue. What am I missing? The OPTIMAX needs 90 PSI of fuel pressure and that's not hard to achieve with a single pump. I'd understand (a little) if they were redundant for safety, but they're not.

[Savage]

For the outboard motor to meet emission requirements ALL the components that effect emissions must be contained, within the motor. The 3 fuel pump system is from the 1990's and is not complex, its rather simple. If the fuel line between the tank and the motor cracks in half, the fuel wont leave the tank and fill the bilge/environment. With a pressurized system (fuel pump in the tank) if the same hose breaks in half ALL of the fuel will leave the tank and fill the bilge, and or the environment... One little spark and BOOM!!

[bigoilman]

This is just "thinking out loud". Even if the safety issue is valid (a simple pressure switch could kill the pump if pressure falls too low) and there's already fuel lines in the bilge so...

Even if that's all true and the Gov't requires it, why not one electric fuel pump?

[Savage]

How's the pressure switch going to work, ZERO- 5 PSI pressure, turn off the pump?

What happens if its a pin hole leak, which causes ONLY a slight drop in pressure, which doesn't cause the pressure switch to turn the pump off, yet still fills the bilge with gas over a period of time? BOOM!

I answered the ONE fuel pump question......A ONE (high pressure) fuel pump system (fuel injection) needs to have the pump in the tank. A ONE electric fuel pump on the MOTOR, can't easily PULL fuel from the tank.

[Jtreed99]

+1, I would never ever want a PRESSURIZED line in the bilge of my boat and the pulse pump is a tried and true safety measure since it can’t deliver fuel unless the engine is running, providing crankcase pressure pulses to actuate the diaphragms.

[rocketman6965]

Thank you Savage. Very eloquent explanation and one I didn't consider when I had a electric fuel pump inline to avoid vapor lock. After explanation, I am glad I removed it

[bigoilman]

Good replies. Thank you. If it's an EPA issue, there's no way around that (not that I'm trying to find one, just curious). And while I definitely wouldn't want a fuel leak in a bilge, I think the chances of that happening are remote enough to make it a non-issue. With either hard lines or PTFE braided stainless steel lines, or the nylon lines that the OEMs have been using since the 90s, line failure is exceedingly rare. Inboards have pressurized fuel systems in the motor/bilge area, no? (<---actual question, I've never owned one). I'm familiar with explosions from not using fans prior to start up and such, so there are proven ways around that (even though they are dependent on the operator.)

Not trying to "reinvent the wheel", just trying to understand.

[Farmer99]

The CG fuel regulations for enclosed engine bays are quite extensive. No pump in tanks, anti-siphon for line cut or rupture, fuel pumps donot run if engine is not running. The previous owner of my houseboat had a fuel pump problem with the generator. Instead of correcting the electrical issue, he wired a switch to the fuel pump, and turned the pump on manually before starting the generator. Imagine if he forgot to turn the pump off and the float stuck open or needle valve was sticking. 200 gallons of gasoline could be pumped into the bilge, then bilge pumps into water or spark and big explosion! I doubt his insurance would have covered the liability.

[EuropeanAM]

+1 on the CG Fuel Regulations- add to that the EPA Standards for low permeation and sealed (non-venting up to a minimum of 5 psi) fuel systems, and it becomes quite the challenge.

And then- unlike the auto or trucks you've transplanted an EFI engine into, the outboard is going to be expected to be able to maintain engine speeds of 5500+ RPM's indefinitely. And it needs to be able to do that in any reasonably conceivable temperature, whether it's an artic climate or equatorial climate.

But: The good news is that they've simplified. Most of the new 4-strokes involve only 2 fuel pumps, and a single-stage injection system.