7.4L ignition problem

[Luke000]

Hello all, I have been working on my mom's boat that has a 7.4 liter Mercruiser in it and we are having problems with the ignition I believe. For the last two years or so the boat would randomly stall while going everything would turn off dead, but it would restart immediately. The recently it's stuck restarting and won't start at all. The engine cranks over good but it seems like there is no spark in the engine. So far I have done little maintenance things like a new distributor sensor, rotor and cap, ignition coil, and like I said battery. But still nothing, no start. It's getting gas and the starter cranked the engine over. Any ideas where to look next? Any help would be greatly appreciated, thank you in advance!!


More info on the engine, its a 1991 with Thunderbolt ignition system

 

[alldodge]

Turn key to ON and see if you have power on the + side of the coil. If that is good, keep the meter there and see if you get a full 12V on the same terminal when the engine is cranking.

 

[ScottMartzen]

You said that it "seems like it isn't getting spark" have you used a spark tester at the end of one of your plug wires to know for sure you don't have spark? Or you can use a timing light. Don't start throwing parts at it with out knowing fore sure there is no spark..

 

[Luke000]

Well I went and tested it this morning before work, I have sometimes 12 volts on positive end of the coil other times I have between 10 and 11 and sometimes I have zero. The boat actually kicked over and ran for about 5 Seconds but then died and would not start again. I tripped for spark with my timing light and there would be one Spark immediately when you engage the starter but then nothing after that.

 

[Bondo]

I have sometimes 12 volts on positive end of the coil other times I have between 10 and 11 and sometimes I have zero.

Ayuh,.... My 1st guess would be a bad ignition key switch,....

 

[achris]

Ayuh,.... My 1st guess would be a bad ignition key switch,....

Or corrosion on the ends of the fuse in the instrument cluster, or a dodgy lanyard safety switch (if equipped) or a bad connection in the engine harness plug, or a bad connection...............

Time to do some proper electrical troubleshooting. Start where you have the problem and work your way back along the wires to the battery. Eventually you'll find a bad connection...

Chris.....

 

[Luke000]

So you guys seem to think it's a bad connection somewhere? I hope so cuz I really don't want to spend the money on a new ignition module at this point. The switch is new as of the spring which doesn't mean it's not bad. Guess I'll be spending the night with my multi-meter and some electrical contact cleaning supplies