My 2003 mercruiser 5.0L, 260 HP MPI has been hesitating lately after about an hour or so on the water. At first I thought it might be an electrical issue. But after further investigation, I found that my "vented" gas cap was missing the rubber O-ring gasket that was supposed to be on there. Is it possible that because this rubber "o-ring" was missing that the fuel tank was not venting correctly and therefore creating a vacuum in the fuel lines which caused the engine to hesititate and sometimes stall out? All the diognostics came back negative on the computer and I've had the plugs, cap and rotor and fuel filter all changed out with the problem not going away. I'm just grasping at straws at this point but am getting a little desperate also. Any advise would be greatly appreciated. Thanks.
