Can't get my 2002 34V up on plane???

mcox

It has twin 350 Mercs with double Brave propellers engines run fine without load up to 5000 RPM and run fine at low speed with load, but won't wind up past 3000 RPM so can't get up on plane.. Bilge is empty.. Trim tabs are set correctly, propellers are not fouled or bent....    Cannot figure it out????

212rowboat

any beeps from the helm?

mcox

No nothing everything is working fine, had the bottom cleaned last year and both outdrives serviced by a certified Mercruiser repairman

212rowboat

the 3k limit seems to be a common thing around here.. not good.. :-(

there are several conditions that will make the computer (assuming you're mpi) reduce power.. most are accompanied by a code (beep).. some aren't .. it seems the fuel systems on these things aren't monitored, or are monitored poorly... a bad MAP/MAF or IAC will usually set a code- but that would be on a single engine and the other would work fine..

how fresh is the fuel filter? regulator?

mcox

fuel filter is a couple of years, not sure on the regulator  What is the MAP/MAF and IAC in laymans terms?   Sounds like I need to get the Mercruiser repairman back out to the boat

Dream_Inn

well, not sure if I want to know how you get to 5k not under a load.  I'm thinking you have EFI, not MPI.  It could definitely be something fuel related & if it only has one regulator for both engines then it could be that.  IAC (idle air control) valve usually affects low end performance as well.  Bad fuel, clogged injectors.  You say you had it bottom cleaned last year?  Some areas require the bottom to be cleaned monthly, have you checked it recently?

212rowboat

Electronic fuel injection and multi port fuel injection are same/same.. throttle body injection is different, though.. :-)

The fuel system is largely unmonitored for some reason... A simple o2 sensor would fix that.. but I digress.. anyway..

If you can hit 5k, however you're doing that, unloaded, then the engines sound to me like they are being starved for either air or fuel... It doesn't take near as much fuel to rev unloaded as it does to rev under load, so I'd guess its a fuel delivery issue.. its both, not just one engine, which more or less makes it a common issue most likely..

Check your tank vent for obstructions.. check the filter- two years is likely too long, especially if its ethanol perversed fuel... Check your regulator.. check your pump..

Maf: mass air flow.. map: manifold absolute pressure.. its either one one the other, engines don't use both.. its two different schools of thought on how to measure air and deliver fuel properly.. iac: idle air control.. each engine has one, it determines how much air to pass when the blades are closed on the throttle body and achieve 650rpm for idle..

Edited: intake air temperature (iat) and maf's are the ones that are differing schools of thought, not maf's and map's.. oops.

LaRea

If your fuel filters and distributor caps/rotors are good, check for bottom fouling.  

I know you had your hull cleaned last year, but odd weather patterns have created severe bottom fouling problems in some locations.  Last year, every boat in my marina had to be hauled and power-washed in mid-season.  We all thought the fuel dock had received a load of bad fuel, but it was bottom fouling.

212rowboat

unless there is evidence to direct a tech deeper, such as a code, it's much better to start butt simple....

check the tank vent.. it may be obstructed.. it may allow enough flow to rev @ 5kRPM, but that doesn't mean it allows enough to flow at 3kRPM+ under load...

same principle with filter(s)... a single fill of bad fuel can cause this, no matter the age of the filters (which is frustrating if a new filter is destroyed, but it did it's job, right?)...

because it's both engines and not just one- I'd rule spark out for the time being (unless the sync function has some sort of limit function that is based off the 'weakest link' engine, but I doubt they were that smart in '02)...

again because it is both engines, I'd rule out air-in-air-out, as it's unlikely that both intakes and/or exhausts are obstructed...

that leaves fuel....

you have a common fuel tank, tank has a single vent, and fuel tank has a common pick up.. I'm pretty sure the water separator/filter is common... that is where the attention should likely be placed first.

TikiHut2

With no profile info we have no clue what kind of enviroment your boat's located in or how well the boat is maintained but I have a feeling that Al (with the mech side) and LaRea (adding environmental issues) hit the nail on the head. 

Bottom fouling seems pretty obvious if both engines run fine otherwise. Slime/barnacles are surprisingly huge performance killers that even massive horsepower may not be able to overcome when you're trying to get your water borne RV to break loose and get on plane. While less likely, a fouled prop may not look too bad but it takes very little to almost completely disable its efficiency.

Let us know what you end up finding, especially if you call the merc mech. It may help somebody else with a similar problem. Good luck, Mike

mcox

Thanks for all of your ideas and comments, I have good info now and can discuss with my MercCruiser mechanic... Will let you all know how it turns out...

brianluck

Good luck

Dream_Inn

Good luck & don't leave us hanging!