Could A Failing Battery Cause No Spark but Still Turn Over

[reece204]

Quick question guys. I have a Mercruiser 3.0 I/O on my 1998 Bayliner and never had any issues. Took it out last week and it ran perfect. Took it out again this week and went to start it and it would turn over but no spark. Checked all plugs and wires and cleaned all connections and checked the spark plugs for wear or indications of flooding and all was good. So I went to the store and bought a spark tester, hooked it up and turn the key and the engine turned over perfectly but it was showing no spark at all. I did notice the battery gauge with the key on was showing about 11-12 volts, but since it was turning over fine I didnt think much of it. So after doing some research I was thinking it was likely the ignition coil. Before ordering a new coil I just decide for the heck of it to try it again, I turn the key and surprisingly, it fired right up and ran normally. I turned it off and on about 10 times and started and ran perfect every time (and the battery gauge showed close to normal this time before starting and 13-14 volts as normal running). So I let it sit for the rest of the day then try it again and we are back to square one, turning over fine but no spark at all from the coil. I called a repair shop and they are still trying to sell me a $200 coil saying that they think that is the problem. My question is, could it actualy be the battery and is it possible that it has enough cranking amps to turn over but not enough volts to produce spark? I didnt think that was possible which is why I am asking. In my opinion, if it was the coil having an intermittent issue you would think it would fail while the boat was running and cause it to lose spark and stall and not only be a problem when starting. To sum it up, today I just turned the key again and it is starting and running perfect once again. I tested the battery before starting with a tester and it showed 12.7 volts. Any ideas?

 

[nola mike]

1. Takes a lot more power to turn over the engine than to fire the coil.
2. It's (almost) never the coil.

I'd start some troubleshooting from here...

 

[GA_Boater]

A late welcome aboard.

Hold off on buying a coil. The intermittent low voltage points to poor battery connections or failing cables. It won't hurt to take the battery to have it tested,

For starters, clean the battery posts and connectors. Also the starter and solenoid connections and the grounds. Make them shiny and bright. And examine the cables for swelling and corroded wire strands.

If you have a man overboard safety switch, make sure the lanyard is on well and the switch is working. Cranking with no spark is the way a MOB switch works, it only kills ignition and the starter works.

 

[nola mike]

If you have a man overboard safety switch, make sure the lanyard is on well and the switch is working. Cranking with no spark is the way a MOB switch works, it only kills ignition and the starter works.

And I suppose check to make sure the shift interrupt switch isn't tripped as well...

 

[reece204]

Thanks for the replies. Today it started normally again which makes finding the fault much more difficult. I did notice one thing though today while the boat was running that has never occurred before. As the boat was at idle I turned on my bilge pump to make sure everything was working okay, and the pump came on and the engine idle stayed perfectly level the tach itself jumped close to 3000 rpm. I shut the bilge pump off and the tach fell back down to the proper reading. I am assuming this may point to a short somewhere? If the rain stays away I will give it a more thorough check tomorrow for loose connections.

 

[reece204]

1. Takes a lot more power to turn over the engine than to fire the coil.
2. It's (almost) never the coil.

I'd start some troubleshooting from here...

Thank you very much for the link. Following these troubleshooting steps I was able to trace the issue to a loose connection in a wiring harness in the engine compartment. The dealer was insisting I order a new coil at $200 (Canadian $) when all it took was a $3 test light and $0 in parts. Thank or all the replies and suggestions guys.

 

[GA_Boater]

The intermittent low voltage points to poor battery connections or failing cables.

Not saying this pinpointed the problem, but for some reason coils are blamed for a lot of problems. Often the act of replacing "fixes" the issue because the connections are better.

Good on fixing your coil with a tight connection! Don't lose that 3 buck test light, it will come in handy again.