Will dead battery cause rough running on a Volvo penta 5.0 GXI.

[albewon]

Thinking about buying a 2003 Larsen with a Volvo Penta 5.0 GXI with less than 300 hours off my neighbor who is experiencing some financial troubles. The boat has been sitting for awhile (2 years). Both batteries were dead (secondary battery used for sound system). Attempted to charge both batteries with negative results-batteries bad. Insured all fluids and belts were in good order and I jumped the engine. The engine started right up; however, it is running rough causing the outdrive to move somewhat violently left and right. Revved the engine and it still maintained a rough vibration. The motor mounts are good.

Question: Will a dead battery cause the engine to run rough? or am I looking at something else?

 

[alldodge]

Yes, the computer needs a full 12V to run correctly. This is not saying that after sitting for 2 years there may be a couple other things causing some problems, don't know

 

[tpenfield]

I suspect that it may be more than just a dead battery, but you should get some fresh batteries in there so you know that you are getting proper voltage to the ECM, etc. If the boat has a volt meter at the helm, that can give you a good idea as well.

With sitting for a couple of years, the fuel may be quite nasty and need to be purged. It doesn't do the fuel injection system any good either.

I would tackle the most obvious things first and move onto the next thing. So, if the batteries are not holding a charge put a good one in there and see if the engine continues to behave badly or smooths out.

 

[dhardest]

If the drive is moving left and right, there may be an issue with the power steering actuator. The valve could be faulty making the pressure on either side of the cylinder alternate high and low. Not sure if the power steering pump might cause something like that either. Check the fluid in the power steering reservoir.

 

[jimmbo]

2 yr old gas doesn't help either. You might have gummed up injectors.