I have a 1995 218 Persuader 350mag alpha drive. Early last year I rebuilt the carb, installed new plugs, wires, cap & rotor. While installing new cap I noticed a black wire with a round crimp lug on the end hanging by the ignition module, looked to me like it should be grounded with the bottom bolt on the ignition module, so I did. Next time out on the water the boat ran best ever, no bog or hesitation at all on holeshot, ran around for about 45 min. then idled around marina for about 20 min., pulled out of idle zone and throttled it, motor spit sputtered and died. Raised engine cover and fired it up, spark was arcing out around coil wire boot and top of coil. HAD to be towed all the way to the boat ramp by a baja. When I got home I took the plugs out 3,5,4,6 plugs were fouled. Pulled carb off went through it again, no problem found, Ive had to other carb experts look at it, no problem found. I took the msd coil off it and installed new msd coil, new plugs, took possible ground wire off ign mod, put old cap & rotor back on, tried numerous coil wires, check spark on at all cylinders, Still fouls 3,5,4,6 plugs no matter what I do to it. Ive also put a timing light on it. I thinking either ignition module bad or photo pick up in distributor bad. Need some ideas, don't know of anyway to test either of these componets, any ideas would be much appreciated. Thanks for the help Jon
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ignition problem???
- Thread starter foyboy
- Start date
BullittBen
Member
I haven't had any experience with a marine distributor, but I know that most auto parts stores can test ignition modules from automotive distributors.
I did have a problem with an automotive module one time where occasionally on startup it would sputter and die. If I turned it off and restarted it would be fine. The module was a cheap replacement, not an OEM. When I put an OEM module in it, everything cleared up.
I did have a problem with an automotive module one time where occasionally on startup it would sputter and die. If I turned it off and restarted it would be fine. The module was a cheap replacement, not an OEM. When I put an OEM module in it, everything cleared up.
happy
Active member
Considering the information, I assume you have thunderbolt 4 or 5 ignition, the black wire should either be comming out of the side of the distributor, or, from underneath the distributor, and it does go to ground, either at the riser, along with the ground for the ignition amplifier, or if it is long enough, the main ground stud on the flywheel housing. If this is the system installed on your engine, adjacent to the ground wire you will also see a white wire with a red stripe, as well as, a white wire with a green stripe.
It is interesting that cyls 3,5,4&6 seem to be fouling out.. Merc used a dual plane intake manifold, in which case these cylinders are not on the same plane, therefore you could reasonably rule out the carburator.. I would think with a single plane intake (it would have to be added by someone else) these cyls could fuel foul..
Noting that the center cylinders are the culprit, i would certainly inspect the exhaust manifolds/risers.. look for rust, water trails running down from where they meet.. separate the risers and look down into the manifold to see if water has been seeping down dowsing down your exhaust valves..
As far as arcing of the coil.. usually the coil tower is cracked.. in which the coil should be replaced.. there is a coil compound (i forget the name of it)that should be used when attaching the coil wire to the coil.. this prevents arcing, and deterioration of the coil tower..
It is interesting that cyls 3,5,4&6 seem to be fouling out.. Merc used a dual plane intake manifold, in which case these cylinders are not on the same plane, therefore you could reasonably rule out the carburator.. I would think with a single plane intake (it would have to be added by someone else) these cyls could fuel foul..
Noting that the center cylinders are the culprit, i would certainly inspect the exhaust manifolds/risers.. look for rust, water trails running down from where they meet.. separate the risers and look down into the manifold to see if water has been seeping down dowsing down your exhaust valves..
As far as arcing of the coil.. usually the coil tower is cracked.. in which the coil should be replaced.. there is a coil compound (i forget the name of it)that should be used when attaching the coil wire to the coil.. this prevents arcing, and deterioration of the coil tower..
Happy thanks for the info. It does have the original dual plane intake, there no mods to the engine other than the coil, which is a MSD anti-vibration coil. With new plugs engine runs good for a few minutes, then plugs start fouling out, thats when spark starts jumpin around coil tower. I installed new msd coil with a msd clamp that holds coil wire on tight. I used to be a technician at GM dealerships, but have never had to work on ignition like this one. I believe this distributor has a pick-up like a Mallory Unilite, which is like a photo eye of some sort, but I have know idea how to check it. I've had three other technicians that I worked with look at this problem and they're as baffled as me, it doesnt make sense why 3,5,4,&6 are fouling out after idling for a few minutes. I'm thinking about slapping a HEI in it to see if that solves my problem, I was just hoping someone out there might think of something I've overlooked. I havent checked my exhaust manifolds internally but external I see know seepage anywhere. Thanks again for your response, any and all info is greatly appreciated.
happy
Active member
Ok i assume you have a thunderbolt ignition.. thunderbolt 4 is denoted by the ignition amplifier being bolted to the exhaust manifold.. thunderbolt 5 the amplifier is attached to the distributor itself.. both these systems use the same cap/rotor and ignition sensor. also, these ingition systems are known for thier reliabilty..
as far as the sensor test.. since it starts and runs.. its gonna pass..
after re-reading the posts.. i remembered about a 31 bullet i had similar symptoms.. it has 502 mags/thunderbolt 4 ignition. the owner complained about spitting and sputtering.. i lake tested the boat... and gps's 72mph around the lake.. then the owner came down and we ran again.. it took 60 miles before the engine acted up.. (long way from home to break down.) we pulled and cleaned the plugs while floating in the gulf.. and they were fouled.. we then ran most of the way home thinking it was carburator related. it then acted up with the throttles pinned.. after a long day on the water it turned out to be the wiring harness from the amplifier to the distributor..
on the thunderbolt 5 version , unplug the amplifier from the distributor and inspect for corrosion or poor contacts.
i would make sure that the wiring harness is in tack, not burnt pinched, or the pins wore out.. make sure your ground from the bottom of the distributor is clean and secure.
as far as the sensor test.. since it starts and runs.. its gonna pass..
after re-reading the posts.. i remembered about a 31 bullet i had similar symptoms.. it has 502 mags/thunderbolt 4 ignition. the owner complained about spitting and sputtering.. i lake tested the boat... and gps's 72mph around the lake.. then the owner came down and we ran again.. it took 60 miles before the engine acted up.. (long way from home to break down.) we pulled and cleaned the plugs while floating in the gulf.. and they were fouled.. we then ran most of the way home thinking it was carburator related. it then acted up with the throttles pinned.. after a long day on the water it turned out to be the wiring harness from the amplifier to the distributor..
on the thunderbolt 5 version , unplug the amplifier from the distributor and inspect for corrosion or poor contacts.
i would make sure that the wiring harness is in tack, not burnt pinched, or the pins wore out.. make sure your ground from the bottom of the distributor is clean and secure.
happy
Active member
i did forget one test... it is your shift interupter switch.. that lil bugger can cause the same problem
the switch is located on the starboard side of the engine, inbetween the shift cables.. its a type of micro switch.. and what it does is stumble the engine when you shift gears.. alowing the clutch dawgs in the lower unit to break.. how it does it is grounds the white green striped wire.. thus taking spark away..
for diagonis purposes you may disable that system.. however if you are underload, and that system is not functioning.. your drive may not come out of gear.. so if you run the boat in this manner.. be so warned.. should you run into a problem you'll have to shut the engine down and shift.. then restart.. this is a test that should be performed on a trailer
the switch is located on the starboard side of the engine, inbetween the shift cables.. its a type of micro switch.. and what it does is stumble the engine when you shift gears.. alowing the clutch dawgs in the lower unit to break.. how it does it is grounds the white green striped wire.. thus taking spark away..
for diagonis purposes you may disable that system.. however if you are underload, and that system is not functioning.. your drive may not come out of gear.. so if you run the boat in this manner.. be so warned.. should you run into a problem you'll have to shut the engine down and shift.. then restart.. this is a test that should be performed on a trailer