Odd situation, no spark

[Brandon5778]

Hi everyone, first thank you for taking your time to read this. Working on a 1975 Mercruiser 888 (302 Ford engine).

Last night I got my boat out of storage, hooked up the muffs and she fired right up. It ran all last season great. Then I noticed a water leak at the water pump hose, because I had removed it last year for winterizing. So I shut her off and readjusted the hose clamp. I went to fire it back up (this took 5 minutes from when it was JUST running) and it turns over but won't start. So I checked for spark coming off the ignition coil, and no spark. With the key on the ignition coil reads about 4.1v, and 9.5v while cracking. It does have the external resistor for the voltage drop. I swapped out the coil along with a new spark plug wire and still the same results. I'm stumped now. My boat does not have a kill switch anywhere.

I'm thinking it has to be something to do with the wiring but does anyone else have any other thoughts? Thank you.

 

[Scott Danforth]

first thing every spring with breaker point ignition....file your points and set your dwell.

point contacts corrode up from non-use after a few months.

while at it, clean your battery cable connections

99.99% of the time it is NEVER the coil

 

[Brandon5778]

Scott, as always, thanks for your input. Last year the boat got a full tuneup with new points, rotor, condensor, and cap. The dwell was set to spec. And I forgot to mention in the original post but the first thing I did was file and clean the points, even though they looked still new. That didn't solve the problem. That's when I unhooked the spark plug wire going into the top of distributor and put it on the block to check for spark while cracking. Every other time I've done this in the past here has always been good spark that will jump a pretty good gap. Now there is no spark coming from the coil. That's what initially made me think a bad spark plug wire, so I replaced it and nothing still. I had a spare brand new coil laying around that I had bought last year so I just threw it on and same results.

​​​​​​Oh, and my battery connections are very clean and tight.

 

[Brandon5778]

I just don't understand why it would have started right up without hesitation the first time. I turn it off and go to fire it up 5 minutes later and THEN nothing. Just seems really odd to me...

 

[Scott Danforth]

I would look at your key switch

if you have anything over 6 volts going to the + side of the coil and you pulse the - side to ground you should get spark the moment you take the ground away. the collapsing magnetic field is what generates the secondary side voltage.

so, either you have no voltage on the + side, or you have an issue on the - side of the coil (either a short to ground all the time on the - side or no contact to ground at all).

 

[Brandon5778]

Thanks Scott, I will check out the key switch and grounds. How do you test the key switch?

 

[Scott Danforth]

see if you have +12 volts on the purple wire when the key is on.

 

[GA_Boater]

With a 5 minute rest and then no start, check the man overboard safety switch. It may have been bumped or dislodged during the 5 minutes. That's if you have one.

 

[Brandon5778]

OK, well I just got off work and got it running but I still have no idea what happened or what even fixed it, so I am definitely not at ease. When I came back from work I tested for spark coming from the coil again and there was a good spark now! So I tried to start it but still not even a cough from the engine. For some reason I pulled the spark plug wire off the #3 cylinder and just let it hang and I tried to start it. It fired right up but obviously was running bad. Shut it off again, reconnected the spark plug wire and now it runs like a top again. So I am completely baffled...

Thanks again Scott, you are always helpful.

 

[Scott Danforth]

your welcome. look for one of these lurking about