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mercruiser 305 ignition problem? 1999

A

arisjunior

New member
HAve a 305 in a 99 bayliner. Engine starts and runs smoothly about 10 minutes and then starts gradually cutting out periodically and gets worse until it quits. Then it will only fire up and run with the key in the start poosition and then dies as soon as the key goes back to run position. Ive swapped out the ignition switch thats not the issue. Someone suggested it might be a coil. Does anyone have any ideas? It has the thunderbolt ignition system.
 
Re: mercruiser 305 ignition problem?

When it cuts out do you check for spark at the plugs.

I stick a spare plug in the wire and ground it at the block while cranking.

You have checked the fuel filters ?

The one in the fitting that enters the carb ?

The anti-syphin valve that enters the fuel tank and the screen on the bottom of the fuel pickup tube.

You have a fuel water sep ? Dump it in a clear container.

While you have the tank open why not suck all the gunk and water off the bottom of the tank with a cheap dc fuel pump into a clear container till you see clear fuel and shut it off.

Finally your fuel tank vent clear ? Open the the gas cap and run it if the problem goes away you solved the problem.

The fuel pump giving between 4-7 psi.

Say all is well could be water in the cab bowl, maybe time for a rebuild.

New fuel eating hose like crazy. your hoses good.
 
Re: mercruiser 305 ignition problem? 1999 305

Then it will only fire up and run with the key in the start poosition and then dies as soon as the key goes back to run position.
Click to expand...

That sounds like the ballast inside the coil is shot; replace the coil.
 
Re: mercruiser 305 ignition problem? 1999 305

arisjunior said:
HAve a 305 in a 99 bayliner. Engine starts and runs smoothly about 10 minutes and then starts gradually cutting out periodically and gets worse until it quits. Then it will only fire up and run with the key in the start poosition and then dies as soon as the key goes back to run position. Ive swapped out the ignition switch thats not the issue. Someone suggested it might be a coil. Does anyone have any ideas? It has the thunderbolt ignition system.
Click to expand...

Same thing happens on all Mopar engines w/ a ballast resistor installed. Always carried a spare. Not saying it's a "Ballast Resistor", but that's exactly how it's acting. Here is the Thunderbolt troublshooting chart. I'll see if I can find the wiring diagram and up load it later if I find it.

View attachment 1700
 
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