Boat Hesitation

I have a huge problem that I need some help on. I was out on the lake yesterday running at about 3000 rmp when the engine in my boat started hesitating. It was like riding a bucking bronco. The boat would almost die out and then speed right back up to 3000 rpm's. When I ran it at about 2000 rmp's it would run great. Any help would be appreciated.
The boat is a 2002 Avalanche with a mercury 5.7 EFI engine.

Maybe a fuel line obstruction? does it also hesitate like that in neutral?

Check Your fuel-water separator and see if You have any water in there.

That sounds like a fuel problem to me too. Did the same thing when I ran out of gas last summer. (Fuel gauge is busted) Replace your fuel filter.

Bad gas??? Are you running a tank from last year?

No this is a fresh tank of gas. I use my boat all year. It wierd how is hesitates only at the higher rpm's. I took it to my dealer to see if they could figure it out. Im hoping its a fuel filter.

Sounds like it is going into limp mode. Of course there are so many different things it could be. Fuel pressure can be good but volume low which would cause what you described.

Have the dealer check the speed sensor. It will bog out at higher speed and RPM if it is failing.

It can also be a clogged line. My mastercraft had a screen before the fuel filter and clogged twice in 5 years with same symptoms as yours. We removed the screen so it can just get caught in the fuel filter and it's been great ever since. Embarrassingly(sp?), mine was clogged with dog hair and bugs both times. I'm much more careful now when fueling up from a plastic tank. Always keep caps on, check before filling for debris at bottom, etc.

350 mag mpi hesitates on throttle up 1 in 10 times. Fule filters fine/new. Anyone have this problem?

Sorry for hyjack.

yes I have this prolbem. Is youe 350 a 2003 model if it is contact and tell him about it. The fix is a new ECM the enginers at merceruiser re program the ECM is what I am told. The dealer just got mine in yesterday boat should be back in the water next weekend

thanks Ill try that!

I love this site.

I have a 97 Mariah with a 7.4 Mercruiser that does the same thing. Mine only does it when above 2500 RPM. It will run fine for an hour or so and then start doing this. I changed the fuel filter but that didnt help. My shop says it sounds like an electrical problem so I took my alternator to the shop and checked that and it was OK. My guages all drop to 0 for a split second every time the engine does it. I have checked all the wiring that I can get to and have found nothing yet. Most people tell me that they think it is a gas problem. I too am running on fresh gas. I'll keep watching your post to see if someone comes up with something that I havent tried yet. This is very annoying to passengers and skiers.

yeup!->definatly sounds like U need to check the fuel-water separator.
I started mine up this spring(doing my own maint.) it was doing the same thing. took the filter off and it was full of water. runs fine now

same thing happened to me. It was a fuel filter. I changed both on my boat. There was one just off the gas tank (small plastic), and one near the engine (metal cannister).

Thanks everyone for your input. Mine water fuel seperator was full of water as well. I changed it and the boat runs awsome.

Finding water in the water/fuel separator indicates that it was doing its job. That's the good news. The bad news is that you must have had water in the gas tank.

It is entirely possible that it is a one time thing and you will never have a problem again.

It is more likely that you pumped the water in from the gas station you filled up at (especially if it was a marina) which indicates that their fuel/water separator is full or otherwise not working and/or they are having problems with water contaminating their tanks.

There is also a possibility that the water is getting into your tank from your boat. Such a thing is possible if the tank vent faces foward or otherwise can channel water into the vent line.

If it happened once, it will likely happen again. Your best bet is to check the fuel separator often. This can be easy if the filter has a drain on the bottom, just hold a glass jar under the filter and let it drain into the jar. If you have any water in there then there will be two distinct layers. The question then is what to do with that jar of gas/water......

If it is water in the fuel tank you can also limit the amount by keeping the fuel tank full. This keeps air from bringing in quite as much moisture into the fuel tank and having it create condensation on the inside of the tank and then drip into the fuel.

Dennis - yours sounds like a loose wire. Maybe on your neutral safety switch. It shuts down the fuel pump and electric system if the circuit is lost.
~S~

I had the same problem at the start of the season. changed out the fuel/water seperator and my secondary fuel filter and then it ran great all the time

My 2002 Mercury 350 MPI does the same thing as Dennis' boat does. Doesn't seem to matter if it's in neutral or running at 3000rpm in gear. I would never have noticed it unless it happened at idle. Everything runs fine, then all of a sudden the voltage meter drops to 0, the engines hesitates, then everything is back to normal. It sounds like an electrical problem, but I've checked all connections as well. Maybe neutral safety switch, but I wiggled the control around and it didn't change.

Very annoying...I have to find out what is causing this.

Trash

I had that happen a couple times a few years back. It was vapor lock.