Surging Issues

[Greg Mallek]

Hey guys, I have an '05 24V with the Black Scorpion motor. Last weekend while surfing, the boat started surging, as if it was starving for fuel, or even water in the gas. I changed the fuel filter, and the water separator, and purged the air line from the schraeder valve, and added a water evaporator to the fuel tank. Today, I went out and ran fine for a bit, then started surging again. Funny thing is that it only happens while in gear. Revs up fine in nutral. At one point, I couldnt get passed 12 mph for a while, but had surges of wanting to go faster.
Any ideas ?

[Nugget]

sounds like you need to take a look at the tranny. Check your fluid levels but may not be that simple.

[boatwakes]

The surging issues with the merc engines is from the small lift pump located on top of the fuel filter. Go to perfprotech.com, type in your serial number and look for the low pressure lift pump, common issue. Surging rpms usually begin about 3000max rpm and then fall to 2400-2600 and surge back and forth. Is that what you're seeing?

[Greg Mallek]

@ BoatWakes: Thats exactally whats happening. Is there a way of checking it out before spending the money? are you speaking from personnal experience, or are you a mechanic?
Thanks !!

[Ewok]

BoatWakes is a mechanic and offers very good info to help fellow TOs diagnose and sometimes DIY the fix for issues.

[boatwakes]

BoatWakes is a mechanic and offers very good info to help fellow TOs diagnose and sometimes DIY the fix for issues.

Thanks, man.
Greg, yes, that's what I try to do. I realize there's a lot of things average dudes can do without having to pay someone and that gives everyone the opportunity to decide if they want to tackle the repair or not. It's important for boat owners to "get to know" their boat and even basic repairs allow an owner to become more familiar with their vessel and thus more safe.

[amharper2k]

I'm curious to know if this fixed your issues as I am having the same problem. Picked up a 03 22V with a 06 scorpion on Friday. I replaced the seperator and spark plugs last night, but I had the wrong fuel filter. Getting one today and gonna to try it out.

[IDBoating]

Funny thing is that it only happens while in gear. Revs up fine in nutral.

This is almost always a sign of fuel delivery problems. "It runs fine on the trailer" or "It only has problems when in gear" both really mean "It only has problems when there's a load on the engine". An engine out of gear, or on the trailer, is only running itself - it's doing almost no work, which requires almost no fuel. It doesn't take much fuel at all to run an unloaded engine up to its RPM limit. But ask it to do some work and the fuel delivery rate goes WAY up, very fast - and that's when fuel delivery problems reveal themselves.

BTW, the time of maximum fuel delivery rate is under hard acceleration (WOT) from a dead stop. That's when you're asking the engine to work the hardest. If you have fuel delivery problems you'll reveal them with that test. I just finished fixing a friend's engine whose high pressure fuel injection pump was starting to weaken and die. At first, he noticed that the engine sputtered at WOT when trying to pull up a skier or boarder. Things got progressively worse until he couldn't even come off of idle in the water. On the trailer, we could rev that baby as fast as we wanted... because it required almost no fuel and so the HPFP could keep the fuel rail pressurized at such a low consumption rate. But in the water, trying to turn the prop, the engine needed more fuel than the failing pump could deliver.

Just something to keep in mind when you have engine troubles.

[amharper2k]

We somehow got it fixed last night. We changed the fuel/water separator, inline filter, and spark plugs (they were showing signs of running very lean). I had filled the separator with gas before installing and primed the lines by turning the key 10-15 times before cranking. I also put a pint of Marvel's mystery oil in a full gas tank. After all that, we put it in the water and had the same issues. Dying at 3200 RPMS. We kept playing with turning the key, checking ground wires, unplugging the pump and running it, plugging it back in, and it progessively got better as we kept playing around. We are not sure what really fixed it, but we believe there may have been some air in the line, possible blockage in the fuel line that worked its way out, or loose connection on the HPFP.

[boatwakes]

Amharper, more than likely you're still going to have the same problem. Since ethanol was introduced to gasoline it's absolutely destroyed marine fuel pumps. If you take the hypothetical that the boat sat for a while before you purchased it, ethanol in the existing fuel and then adding mystery oil (which actually most likely solved the immediate problem by lubricating the pump) you may make it through the season, but be ready for it to happen again. Keep us posted.

[Wakeman22]

So to continue on this fuel issue...

I am having the same affect with my 07 24ve. However it is worse and can't get above 1500 RPM or less. Seems like a bad gas problem similar to issues I had years ago. I got marina fuel and suspect I got some bad gas. I added 15gallons of fuel from the land based station and seafoam. Still have the issue and it is getting worse. Mine is the MPI 360 engine.

What and where should I be looking at? I am going to start with the fuel filter. Where is the water separator? And where are my fuel pumps?

[IDBoating]

Personally, I'd start by measuring the pressure on the fuel rail as you ramp up the RPM's. Does it behave this way both on the trailer and in the water?

[Wakeman22]

While in neutral it revs fine but with a slight miss. While in gear and under load it cuts out. Pulled the fuel filter yesterday and it looks good. No water in gas. May just be bad fuel similar to what has happened before. However today I am going to replace the plugs and then run it with fuel pressure gauge attached to see where it is at. What should the PSI be?

[boatwakes]

Wakeman, when did the issue start, immediately after getting marina fuel or another time? What motor? Does the fuel in your fuel filter smell the same as fuel from the station? If there's water in the fuel it will smell like alcohol but you won't be able to see any difference in the fuel.

[Wakeman22]

Yes it began soon after getting fuel. I have had this issue before. I believe it was probably Ethanol that went bad. The problem is that it detonates early and the knock sensors sense it and retards the timing making it worse. I added 15 gallons of regular fuel. Did not help. I added octane boost and it run great again. I the filled it with fuel from a Marina that has regular gas. Runs out perfect.

I would probably say that 80% of running issues in boats is fuel related. Either from sitting too long, Ethanol in fuel or contaminated gas. YMMV.