Mercruiser running problems

[RoisandPhil]

I have a 220 hp 1999 Mercruiser 5.0 EFI. I took it out for the first time this season last week and it ran well for about twenty minutes until I backed off the throttle to about half way at which point the boat stalled. It took about ten minutes to get the boat started again and I managed to labor into shore. The boat engine was running very rough with a bit of vibration and once or twice sounded like it may have misfired. It felt like the boat wasn’t getting any fuel. Anytime I would touch the throttle either up or down the engine would stall. I was lucky to get back to shore at a constant throttle setting. I changed the water separator (no sign of water) and cleaned the flame arrestor. Back on land connected to a hose I managed to get the boat started again and it ran fine while adjusting the throttle up or down for a while. Then the problem started again and immediately after starting I would have to give it considerable throttle to keep it running. Again after running, if I dropped the throttle the engine would just die. I am pretty sure it’s not a contaminated fuel problem as I dumped the contents of the separator into a glass jar to look for separation. Any help would be appreciated.

 

[hoot]

Re: Mercruiser running problems

you're lucky that it duplicates the failure on land. check for spark. pull plug wire, hold close to plug and observe spark strength. duplicate failure and do the same. heat generation can affect ignition coils and modules. and check fuel filter(s) and vents. give the boat a good going over from the ignition and fuel side.

 

[RoisandPhil]

Re: Mercruiser running problems

Thank you. I will try this at the weekend and let you know how I get on.