Guys,

I'm working on someone's boat in the facility where I store my boat, helping this guy out. He has a 1996 Maxum, w/ a 350 SBC alpha. He just had the engine rebuilt to stock, engine ran on in the machine shop after put together to set the timing and make sure all was good for the guy. I am helping install the motor into the boat and get it back to together and running. Got the boat all set for the flip of the key and she is not starting. I checked for fuel, there is plenty of that, carb is squirting fuel. I checked spark at a plug with a screw driver grounded and nothing. I then proceeded down the Thunderbolt troubleshooting path.

1- I checked the coil positive, it had power (test light) when the key was on and the kill switch was on.
2- checked the red/white wire from the ignition module and it had power. (test light)
3- Disconnected the two coil negative wires, put a test light on them, no power, so I will say the tach is not grounded out.
4- I tried cranking the engine with test light hooked up to coil ground wires and all wires hooked up to ignition module, no light.
5- I did test restistance of coil primary, and it was something in range, then tested the coil secondary loop and it was a magnitude higher, so I figure coil is fine.
6- disconnected the green/white wire, kept the red/white hooked up, and struck the green white wire from ign. module to ground quickly with key on and I did see my test light up very brightly as I touched to ground.
7- SO I determined it was the distributor sensor.
8- I ordered a new sensor, installed it, ground wire is hooked up on back side of block to where the ground from the battery attaches.
9- I also had ordered a new coil as the old coil was original and secondary contact was a little corroded. (cap and rotor on distributor were already new)
10- Everything is hooked up, tried cranking the engine, nothing. At one point I thought there was a "little life" as engine caught for a split second. Then another time I watched as I **** it down/stopped cranking that it kicked back to go. BUT NOTHING.
11- swapped back to old coil. Same NOTHING.
12-tested the red/wire from ignition module, 11.2volts. battery was 12.7 I think, maybe 12.4 volts.
13-Hooked red/white wire back up, Disconnected coil negative to my test light, tried cranking engine, had intermittent light.
14- Hooked up red/white and disconnected green/white and touched those wires to ground and my test light light up. SO that tells me the ignition module is fine.
15- Hooked up test light to the green/white from the ignition sensor and cranked the engine. My test light would light up, but very sporadically, sometimes when done cranking the light would stay on. But light flashed a few times during a cranking session....3 or 4 times total.
16- Had an thought over the night and disconnected the alpha shift interlock, tested it all over, everything the same, intermittent lights on my test light as cranking.
17- I ordered ANOTHER sensor. Will have it this weekend. WHAT AM I MISSING?

Can I put straight 12 volts wire from battery to the red/white on the distributor sensor, to make it 12.5volts vs the 11.2 to see if I get more frequent ground signals to the coil? Is that 11.2 OK? Is the ignition module crapped out. (Swear in my ignition round of testing I put my test light on the red/white from ignition module and my test light lite up. After I got new sensor and had no start conditions, I started to use my FLUKE meter and noted the test lamp would NOT light up bright, yet had 11.2 volts. Is this ignition module dead/dieing? Is there a straight up way to test that? Im going nutz.

I appreciate your help guys.

Chris

Just saw your pm, sorry, don’t ck boat sites much this time if year. It’s sledding season. Braap.

Anyway, i don’t read long things well,
did you go thru charts like this ? For testing when notvrunning, 12 volt things can be less volts. Just matters there is some. Running, things coils like 12+

Anyway…….

Thanks for the response….. yes I did use a chart like that.

if my 11.2 volts is ok on the red/white from ignition module, then it all points to the sensor again. I just can’t believe a brand new sierra sensor would be crap out of the box.

Yup, 11 volts totally fine.

who’s module ? Merc ? Sierra ? Ching ling mi ?

lol.......Im like you got through the first paragraph then......

Haha…. I’m like you guys too…. Dreaded posting all that…. But wanted to give as much detail. Sorry for that.

the ignition module is OEM mercruiser. The sensor that was just bought was sierra and appears to be crap out of the gate.

I just bought another one, this time CDI unit.

so I will test that one this weekend when arrives.

thanks for the confirmation of the 11 volts. That’s assuring as I was starting to think maybe the ignition module.

And to conclude here, the problem was in fact the ignition sensor. A brand new Sierra unit was bad out of the box.

Ordered a new CDI unit, installed and saw the proper flashes on my test light, hooked it up and engine fired right up.

Congrats