I have a 02 380 sundancer . When...

[filimili]

I have a 02 380 sundancer . When fuel tank goes below 1/3 full on starboard side the starboard engine will lose rpm at speed . Marinemax guy said he thought starboard fuel pump going out . Although it didn't do it when he came for ride w me . Any suggestions ? 

[wingless]

My assumption is gasoline 8.1 engines.

Has the fuel pressure been monitored at the fuel rail w/ a gauge?

There are fuel cutoff solenoids, one for each engine and one for the generator.

The fuel cutoff solenoids used on mine have an electrical enable and also have a twist knob.

The logic on the twist knob on the solenoids used on my boat are: fuel flow only when electrically activated or always on.

[filimili]

No it has not . I wouldn't ever be able to do that myself . Is that how you tell if it's fuel pump ? I made a 200 mile round trip last wkend . Ran great til 1/3 tank then started acting up . Just like previous times . Never happens when more than 1/2 tank . Changed all filters too . Yes 8.1 s . Is it possible that increased pressure from full tank assists a failing fuel pump ? I'm a doctor not a mechanic . Just trying to make sense of situation . Appreciate input . Knowledge is power .

[wingless]

If the engine cannot ever run after 1/3 tank then I would guess there is a hole in the pickup tube so it is sucking air that is easier than sucking fuel.

It might be that the problem does not directly correlate to the fuel level. That would not be my first guess.

The invaluable tool required for the arsenal is a fuel pressure gauge. The engine won't go w/o fuel pressure.

The usage is "easy". It screws onto a standard Schrader valve, like on a bicycle, on the fuel rail feeding the injectors. The main concern is that fuel is very flammable, so connecting / disconnecting / usage needs to be done w/ appropriate care, especially on top of a hot engine and in a closed compartment.

There is negligible difference between sucking from a full tank and one w/ 1/3 gone.

The other suspect is a poor electrical connection on the fuel shutoff solenoids. They are on the forward wall of the engine compartment. How do the electrical connections look at that point?

Assuming your Parker / Skinner fuel solenoids are like mine, then try operating the engines w/ the twist valve arrow pointed to the left, to off, so it provides fuel only under electrical control. Then if there is a problem, twist the knob to the right, to on, so it always provides fuel. The normal default operation should always be w/ the arrow to the left.

Otherwise treat the boat like a patient, "it hurts when I do that", "don't do that".

[filimili]

Thanks for your suggestions . You've given me some homework to do . It's just so strange that it'll run flawlessly for 7-8 hrs at all speeds then it'll start acting up . When it does act up l drop rpms on both engines all the way down - run slow for a min or 2 then power up both engines . At this point it'll run well for a few mins or 30 min before it starts acting up again . Until I fill up again .

[wingless]

My 454 Horizon Magnum engines (7.4) also have fuel pressure regulators. These are spring-loaded vacuum diaphragm regulators that are plumbed to the intake plenum to control fuel pressure proportional to engine rpm.

The Mercruiser implementation is very poor and these require periodic maintenance for proper operation.

My hope is the engineers who "designed" that system on my earlier engine were retired before they had a chance to duplicate it on yours.

The engines require sufficient fuel pressure, especially at speed, to maintain proper rpm / power.

[wingless]

Why not run both tanks low, in-case there is fuel contamination? Throw in some fuel cleaner / dryer while it is low, to help get any contamination out of the tank. Do it while low to avoid dilution. Those bottles are designed for cars w/ about 15 gallons, not a boat w/ ~120 gallons per side.

Then after topping off both tanks change both fuel filters.

All 16 of my injectors were sent out for cleaning and testing. They found problems that required some to be replaced. It was well worth the cost and effort!

[wingless]

"When it does act up l drop rpms on both engines all the way down - run slow for a min or 2 then power up both engines . At this point it'll run well for a few mins or 30 min before it starts acting up again . "

The two engines are completely independent. Each has it's own ECU, it's own fuel supply and it's own electrical supply.

The most common way one engine can affect the other is that when an engine's output drops significantly, such as pulling back one throttle while on a plane, the rpm of the other engine will drop. The boat is designed for both engines to rotate at the same speed. The engines cannot / will not maintain rpm if one engine drops out.

It is most likely that the problem is related to one engine.

[filimili]

Found the fuel pump solenoids . Found way to turn to off . They are both pointed in on position . If I turn to off and turn engine on I'm not sure what I should be looking for or how to interpret results . Can you advise ?

[wingless]

Assuming your Parker / Skinner fuel solenoids are like mine, then try operating the engines w/ the twist valve arrow pointed to the left, to off, so it provides fuel only under electrical control. Then if there is a problem, twist the knob to the right, to on, so it always provides fuel. The normal default operation should always be w/ the arrow to the left.

If there is a problem while pointed to off that is eliminated while pointing to on, then either the valve is bad, or the electrical signal controlling the valve is bad.

Where were they pointed up until now?

[wingless]

The other suspect is a poor electrical connection on the fuel shutoff solenoids. How do the electrical connections look at that point?

[filimili]

Electrical connections look very clean . I turned solenoid to off and ran engine at ideal for 20 min . Then put back to on position and ran for 20 min . Ran great both ways . Still don't know what that means or how it's related to why my starboard engine wants to occasionally reduce rpm at speed .

[wingless]

Keep all three solenoids always turned to OFF, Port, Starboard and Generator. If the problem happens, first attempt to determine which engine is misbehaving, then turn both Port and Starboard from OFF to ON.

If there is no effect on correcting the problem, then the fuel cutoff solenoids are not the problem and they may be returned to the OFF position. Normal / safe operation is w/ all three solenoids in OFF position.

Ensure the electrical connections are tight and secure, both the nuts retaining the ring tongue connectors to the solenoids and the ring tongue crimp to the wire.

My guess is still a fuel problem, like: dirty fuel (fix by running tanks very low and adding cleaner / dryer, running some more, topping off tanks and changing fuel filters); insufficient fuel pressure (maybe bad pump or fuel pressure regulator problem, monitor fuel rail pressure before and during problem), or bad / dirty fuel injectors (check electrical connections (16) are secure, send injectors for cleaning / testing).

Good luck!

[filimili]

All solenoids were in the ON position . I'll run it this weekend in OFF position and see what happens . Thanks for your help .

[wingless]

Because the problem happened w/ all three solenoids in the ON position, then the problem is not the solenoids.

Keep all three solenoids in the OFF position and move to investigating the other potential issues.

[Vermont_Sundanc]

I have a 2003 SD 340 with gas 8.1L. I'm having the same problem--happens to be the starboard engine. I can't recall the fuel level but the RPMs are matched, boat is running great and then the starboard engine drops in power by a few hundred RPM; noticeable and it will knock it off plane. But I've been moving the starboard stick forward to give it more throttle to match RPM with port. After 30-60 seconds, the starboard engine quickly ramps up its power and I'll bring the starboard throttle back to match the port. Yesterday, on a 1.5 hour cruise at 3300 RPM, it happened twice. Any additional advice would be appreciated. Thanks in advance.

[SMT]

If this is a diesel it could be an indication that the fuel solenoid is about to go out or a relay. They are easy to check with a volt meter. Also check your fuel filters to see if you are sucking some air..

[Vermont_Sundanc]

Hi SMT - they're gas engines. I'll take a look at the fuel filter. Thanks for the response.

[wingless]

The OP sent me a PM that the Marine Max service was to exchange only one filter per engine. There is also a second fuel filter per engine that resolved the problem once replaced.