Mercruiser 188 Coil gets hot/loses spark

[Fuss188]

Hello All!

I have a question. I've got a 1973 Slickcraft SS-215 with a Mercruiser 188 (Ford 302). I've been chasing a loss of spark problem for a while now. Supposedly the engine was recently rebuilt by the previous owner. Not sure if he ever tested it in the water after the rebuild or not. So, the boat starts up and runs great initially. But eventually, it will just die while under way or not restart after shutting it off. I believe I've narrowed it down to it losing spark. I attribute the spark loss to an overheated coil. Now most would assume that the coil is bad and put a new one on it. I've done that.. new coil gets hot just like the old. This year of ford engine uses a ballast resistor wire to limit the voltage to the coil. I've checked the resistance on the wire and it's about 1.8 - 2 ohms. Is that too much?? the wire's integrity appears to be intact and the readings don't change while massaging the wire. I need to figure out what is causing the coil to over heat! This is what I've done to the boat so far:

New Impeller last year
new plugs, wires, cap, rotor, points and condenser
new ignition switch
new coil
Removed and clean all grounds and positive terminations
Rebuilt Holley 2bbl carb
new 140f thermostat

The last time out, she ran beautifully for about 45 minutes.. came back to the dock and shut it down to adjust the fuel gauge float. engine was off for maybe 15 min. Then it wouldn't restart. Threw my in line spark tester on it and no spark. Checked voltage to coil with key on.. 8-9volts.. right where it should be. So then I told my buddy to crank it while I watched the meter to be sure it was getting the full 12V while cranking. Well the damn thing started up like there was never a problem! So we idled over to the marina and got some gas. Shortly after leaving the Marina, while idling through a no wake zone, it just died. we got her to the side where i realized the coil was Hot! I switched it out with the old coil and she fired right up. Troubleshooting was the sole purpose of this trip so we decided to go out on the lake and continue. Boat runs great until the coil heats up. What, other than the resistor, could cause the coil to get hot? I did notice the new dist cap I put on seems to fit poorly. Not like the original. And while the engine is running I can physically hear the arcs inside the cap.. but erratic.. not uniform like one may expect. Could a poorly made distributor cap cause the coil to overheat? However, I feel like the no spark problem existed with the original cap as well. this is my second season chasing this issue! I'm getting good at breaking down!! LOL. Any insight from you old school guys would be greatly appreciated! I should also mention that I'm not 100% sure the engine is cooling efficiently. Which I imagine could cause the coil mounted on the intake manifold to get hotter than usual. The systems normal operating temp should be 160f. I don't believe my gauge works properly so I've been using a laser therm to take readings on the engine. The highest reading I got was 186f on the intake next to the temp sender. Not extremely hot but hotter than the 160 spec. The water pump on the engine is not leaking but I can hear a slight knock at an idle that could signify a failing pump. I have no reason to believe there's anything wrong with the engine internals. I plan on removing the belt today to check the pump shaft for play and make sure it spins freely.
Again.. any ideas you guys could throw my way would be awesome! I've got alot of time wrapped up in this thing! It's a beautiful boat! Just need it to run right!!

Thanks

 

[alldodge]

Is condenser between .18 - .25 MFD

Which distributor is installed?

Do coils meet spec listed here

http://boatinfo.no/lib/mercruiser/manuals/mercruiser2.html#/672

 

[Fuss188]

Points and condenser replaced last fall.. Not sure what MFD stands for..? I set the points at .018 if i remember correctly..

I believe the distributor is the original for that engine.. have no reason to believe it's been changed. Still seems tight, no shaft play.

As far as the coil goes.. I first tried one I bought at Napa they said should work.. problem remained
Next I looked up and ordered one specifically for the mercruiser application.. problem remains..
So I have 3 different coils that overheat and cause the engine to die.. 2 of which are new.. at this point I'm a bit skeptical it's a coil problem and more of something causing the coil to get hotter than usual..

Note: Setting the points is as far as I've gone when referring to timing.. could the dwell being off cause the coil to heat up?

 

[nola mike]

Setting points by dwell is basically just a more precise way to do it than by gap. As AD alluded to, a bad condenser causes increased sparking/wear at the points, though not aware that it would affect the coil (MFD= microfarad, the condenser is a capacitor). Timing too far advanced could cause the engine to run hot, but don't think it would affect the coil either. However, the point gap/dwell/timing/idle are interconnected, so you need to adjust all of them when adjusting the points. Have you verified that you're not getting full voltage to the coil when running? Also, does it start right back up when you switch coils every time?

 

[Fuss188]

Right on.. As I said, I have no way of knowing if the engine was tested under load after it was rebuilt so it's very possible the dwell is off.. it just seems to run so good when running I assumed it was fine. I have experienced a slight surging at idle from time to time.. I've checked the voltage to the coil multiple times while running and it always checks out at around 9V. There have been 2 instances where the engine died, I swapped coils and it fired back up. That being said.. there have also been times where it died.. we sat floating about for ten minutes and then it started back up.. but only runs for a few before dying again. When I switch coils it seems to run much longer.. leading me to believe the coil is overheating.

 

[alldodge]

Electrical things heat up because of current. A coil should not get much beyond warm. The manual does list 1.8 to 2 ohms for resistance wire, but may want to try a 3 ohm balast resistor based on coil findings

Measure the coils and see if they conform to the pic

 

[alldodge]

Also what kind of plug wires and spark plugs are being used?

 

[Fuss188]

Thanks alldodge for confirming the ballast wire specs! I haven’t been able to get a straight answer on that. I got the plugs and wires from Napa who.. again.. said should work fine. The wires are like double the length of the ones I pulled off! Universal I guess? I plan on replacing those as they look terrible with all that extra wire laying around.
I was just poking around and decided to explore the erratic spark noise I was hearing from the distributor cap. I compared the new rotor I put on in the fall to the old one. The new rotor is about 2.5mm shorter from center to tip than the original. And it has signs of arcing from the top of the pickup... You think this could be my problem?

 

[alldodge]

Was asking about wires because to see if they where resistance wires. Every bit of extra resistance is good because the current decreases. Even plugs can add to the extra current if they are not resistance

 

[Fuss188]

I don’t believe they are resistance wires..

 

[alldodge]

I don’t believe they are resistance wires..

If there not, there is some extra heat on the coil. That said, they don't make many non-resistive wires anymore

 

[Fuss188]

Yeah.. My end goal is to drop an HEI distributor in it and eliminate the points all together. Tried finding the conversion kit for my distributor and was told twice by two different people that they just don't make them for this year distributor. So until I have an extra 5 bills laying around I have to make what I got work. I don't remember what kind of plugs I put in it last year but I think I remember those were a task to find as well! I'll have to check on that. I also put the original rotor back on so I'll let ya know if that makes a difference. Thanks for all the replies thus far! Keep the ideas coming.. you guys are great!

 

[alldodge]

Have you looked at Pertronix or Mallory conversion kits

 

[Fuss188]

Yeah.. I was told that they don't make a conversion kit for my particular distributor. So I'd have to buy a whole new distributor. He said there was a span of a few years that the conversion kits won't work in and mine just happens to fall in that category. Seems to me he had a hard time finding the spark plugs too.. or didn't have any.. I think I ended up buying the plugs at Napa.. This was the guy at our local boat shop/parts store. I've never gotten bad info from him in the past so don't really have a reason to not believe him. Anyways, with the shape the boat is in, I figure it's worth the extra $ to just do the whole distributor and be done with it.. But for right now I need to figure out the prob with the existing system so I don't worry with my kids on board.. Also being 39 years old, points systems are a bit before my time. So I kinda like the challenge of trying to figure this stuff out. As technologies move forward, knowledge of the "old school" stuff tends to fall by the way side. I like to learn as much as I can.. frustrating as it may be.. Once I prevail over this.. I'll go buy a new distributor.. LOL

 

[alldodge]

I did a quick look and both show they fit your motor. I would email either or both and get the scoop from the vendors

 

[Fuss188]

Right on.. yeah I guess that’s worth exploring a bit further.

 

[justinshreve1986]

i also have a 888 merc and having some what of the same issue did you happen to figure it out

 

[justinshreve1986]

was any one able to figure out the spark issue

 

[achris]

Turn the engine until the points are closed (or ground the - terminal of the coil with a jumper), measure the voltage on the + terminal on the coil. Should be around 7-8 volts. If it's 12v, then the resistance wire is not 'resistance', the coil is getting too much current, and will get hot and stop working.... (or the minus terminal isn't grounded )

Check you have the right coil, should be around 1Ω primary resistance. If it's 3Ω then you have the wrong coil, and it'll get hot and stop working.

 

[Fuss188]

Thanks Achris, I have checked voltage at the coil while running and it was around 9V. Did not ground the (-) side.. though. I just got the engine harness back on after removing it.. I cleaned up all the ends and tested every wire for continuity as well as a visual inspection. Also checked the resistance wire extensively.. even heated it up with a heat gun to see how much the resistance would change. It appears to be good and right within spec. The last coil I bought was supposedly specifically for the mercruiser application. But I will def check the primary resistance again. Haven't fired her up since I got the harness back on, but plan to button everything up and take another test run in the next few days. I also compared the rotor i put on last year to the original I pulled off. The new one is about 2.5mm shorter and appears to have been arching erratically judging by the burn marks on it. I cleaned up the old rotor and put it back in so we'll see if that makes any difference.. I'll keep ya posted..