Hey Guys. Having issues with my 2001 5.7 EFI Mercruiser mags not reaching full throttle or rpms

Aprice

Hello Gang. I have exhausted my options and had no where else to turn. I know the power of this forum and trust the experience and expertise within. So, I bought a 2001 Maxum 3300  SCR 2 weeks ago. Had to trips without any issues. Anyone have any experience with loss of power, lack of power while trying to get on plane? I have twin 2001 Mercruiser 5.7 Mags EFI that would not go wide open throttle, would not go above 2800 RPMS in both motors and took almost 5 mins to get fully on plane, with me using tabs, lifting drives to find a sweet spot and once I was on plane I could not get the motors to go above 3800RPMs. I had tons of throttle left in the shifters and the engines didnt respond. This was a week ago. Today I took her out and got on plane quickly (things seemed good) and had the both motors at about 4200RPMS then lost power in the port and it stalled. Couldn't get the port to fire back up. Limped in on my starboard. I bought the boat 2 weeks ago and didnt have these issues the first time I had her out or during the sea trail. Not sure if maybe bad fuel or fuel pump /pressure issue. The filters were new beginning of season. Any one have a similar experience or issue and can help out please let me know. Thanks in advance.

Aqua_Aura

You'll get all sorts of help here! How old is the fuel? You can borrow a fuel pressure test gauge from places like O'Reilly or AutoZone. Have you checked plugs, possibly pull them and check conditions, also what about wires.


Since it was an issue with both engines I would definitely start with the fuel in the tank. I had an issue with bad fuel at the beginning of this season and added some fuel stabilizer and it got better and now that I got some fresh fuel after burning about 50 gal. All seems well. 

aero3113

I would replace the fuel filters and see how she runs. You might have inline filters along with main filters.

Michael T

@Aprice.....you are sure your shift cables have not slipped, are not binding?

212rowboat

for grins, can you check the fuel vent for obstructions?  some have a check valve/gate thing... others have a "J" trap which should be oriented upward (not downward like under your kitchen sink)... IF it's oriented downward, it could be holding water and not allowing the tank to vent- which makes the fuel too hard to pull from the tank... if it's obstructed (valve stuck, some sort of debris in it) it will do the same thing... 

quick way to tell- when you encounter this, simply open your gas cap and see if the engines run right... 

but... in the end... this sounds like old gas. 

Michael T

......if your fuel vent and gas cap are not allowing your tank to pressurize creating the equivalent of a semi-vacuum condition, when you remove your cap you may hear a rush of air.

212rowboat

another option IF it's not bad gas is a vapor lock on the cool fuel unit, which can be eliminated by routing the return back to the tank.  

reneechris14

Start small filters,plug,cap and rotor. Third or forth time out sounds about right to stir up things if they have been left alone.