Engine starts on release of switch only

[Mark Jones]

1989 4.3LX Mercruiser will crank fine and turn over and over but will only start (fire-up) when I release the start switch. Sounds like the switch is bypassing the coil voltage during the start postion and I'm getting just enough fire when I release the switch to start the engine. How do I correct this?

 

[mkast]

Re: Engine starts on release of switch only

Replace the ignition switch.

 

[stonyloam]

Re: Engine starts on release of switch only

When your engine is running the coil gets its (reduced) voltage through a resistance wire (purple from the choke?), however when it is cranking it gets its (full) voltage directly from a wire (probably purple/yellow) attached to the starter solenoid. A poor connection to the starter will act exactly as you described (no, or very much reduced voltage to coil when cranking). Check out that P/Y wire on the coil. If the starter is cranking, the switch is OK. Not too familiar with the V6 but I think all of the wiring on that vintage motor is similar. Good luck.

 

[Don S]

Re: Engine starts on release of switch only

When your engine is running the coil gets its (reduced) voltage through a resistance wire (purple from the choke?), however when it is cranking it gets its (full) voltage directly from a wire (probably purple/yellow) attached to the starter solenoid.

That's how it works with a points distributor, but not with his Thunderbolt IV electronic ignition.

Not too familiar with the V6 but I think all of the wiring on that vintage motor is similar.

In 89, only the 3.0 and 3.7's still used points type distributors.

 

[stonyloam]

Re: Engine starts on release of switch only

Dang, and I thought I knew what I was talking about on that one:facepalm: Looked at the wiring diagram, and would still suspect electrical problem. Since purple on a Mercruiser is usually +12V with the ignition on. I would measure the voltage at the purple wire + terminal of the coil with the ignition on, and while cranking to see if there is a significant voltage difference. Guess it could be the switch. Apologies to mkast, and thanks for the correction Don.

 

[Mark Jones]

Re: Engine starts on release of switch only

It was the switch. Not a faulty one but loose connections. Fires right up now. This also resolved a very intermittent low voltage reading I was getting on my voltage gauge. Thanks for the help in pointing me in the right direction.