Mercruiser 188 Coil gets hot/loses spark

[Fuss188]

Justinshreve1986, as I mentioned above, I have done a few things since the last time I ran it but haven't had time to test it yet. I'll let ya know how it goes. Here's a list of things I've done to mine just for reference:

Replaced plugs, wires, cap, rotor, coil (twice!), points and condenser.
Replaced ignition key switch
Replaced starter
Cleaned and rebuilt carburetor
Replaced Impeller
Replaced thermostat
Replaced battery
Removed and cleaned up every single ground I could find on the engine and elsewhere. (All positives (+) too)
Removed engine harness, cleaned ends, inspected and put back on.
Oil change
Replaced water/fuel separator.
Sucked all fuel out of the tank and replaced with fresh
Cleaned fuel check valve and redid line from tank to carb.

I think that about covers it. I know some of those items have nothing to do with the ignition but I was dealing with multiple issues from the start. So now I've got it running great with the exception of this pesky spark issue! I'll keep ya posted on how it does on the next run..

 

[Scott Danforth]

you replaced the coil twice and the issue is still there because it wasnt the coil

its rarely the coil. about 3 coils out of a million changed are actually bad.

coils do get warm, usually on a boat, they get to about 180-200F (about 30-50 degrees warmer than what you can touch). under the hood of a car running coolant temps about 230, coils get to about 250F

most of the time when you loose spark with points, either something is grounding out the negative side of the coil (usually the condenser) or there is a short somewhere to ground from a wire chaffing, or the points are either not opening or not closing

no where have you posted what the actual dwell is when you measure it. insufficient dwell leads to a weak spark. a weak spark will not jump a gap as well.

in post #8, you stated your rotor is shorter and you have signs of arcing. this is too large a gap you wont have a continuous spark

Also, if you have severe arcing, you get arc trails..........and if you have arc trails in your distributor, its not that you are losing spark, its just that you are firing all plugs nearly simultaneously. if you want to screw someones day up, pull a dizzy cap and draw a line to all the contacts with a #2 pencil. the carbon trail will cause the spark to jump everywhere except the cylinder you want to fire. (this was an actual test from Autos 101 in high school 35 years ago)

both pertronix and mallory (now listed as sierra at double the cost) have electronic triggered dizzys, and both require a ballast wire or resistor just like points, and both will suffer the same issue if you put in too short a rotor or have arc trails

 

[Fuss188]

So the last temp reading I took on my coil was about 180F.. so maybe it's not that the coil is getting hot, but the rotor was causing the issue..? I originally assumed the coil was getting hot because when it heated up I would lose spark to the plugs. Someone told me the coil shouldn't get hotter than warm to the touch. But what you say makes more sense because the entire engine compartment gets hot under load. Also, I was reading your response in justinshreve1986's thread and you mentioned that if the tacho is bad it could cause issues. My Tach seems to work ok but does act a bit funny from time to time.. I haven't drawn any correlations between the two but will keep an eye on that as well if the problem persists. I really want to get out there and test it this afternoon but I have a dentist appointment. Hopefully they don't drug me up too much!

 

[Scott Danforth]

if your tach has a short, it will ground out the negative side of the coil, effectively shutting off the coil (same as the shift interrupt switch does). so disconnect the grey tach wire at the coil and go boating.

who ever told you a coil wouldnt get warmer than you could touch with your bare hand doesnt turn a wrench or understand engines......everything bolted to that big block of iron is going to get as warm as the big block of iron or warmer if it also generates heat, like a coil, starter, and alternator do

 

[kenny nunez]

If you have a Prestolite or Mallory distributor adding a Petronics kit should be no problem. There were 2 other distributors that also were used, Holley and Ford. The Ford model uses regular Ford points but I am not sure if a Holley kit was ever made.

 

[Fuss188]

Thanks Scott! and If the prob persists I will definitely try disconnecting the tach.. As far as the coil, the guy that told me that meant well, but it's clear that was false info! Thanks for clearing that up.

Kenny, Is there a good way to identify the distributor? To be honest I haven't really looked into it real far yet. I believe the cap I took off said Mercury Marine on it.. kind of a dirty beige color w/ each wire numbered.. I'll have to take a closer look at it for future reference. So does that mean if it's the Ford model, there isn't a conversion for it?

 

[Scott Danforth]

Mallory has drop in modules like the pertronix ones for their older dizzies..... including the ford dizzies Holley is Mallory in this case. look up the Mallory 6100x series e-spark modules

 

[kenny nunez]

Try to post a picture of the cap and the way it is retained and the points and condenser how they are mounted.

 

[justinshreve1986]

i am still having the same issue as you are and i set my points at .020 with a feeler gauge and still having the same issue

 

[justinshreve1986]

i also changed my cap on my distributor as well

 

[justinshreve1986]

ok so after further looking into things i took all the wires off my coil which were two brown wires and the points and condensor wire going to the negitive and two white wires going to the positive side of the coil and only the one white wire had power going to it the other wires did not. my question is are all of the wires supposed to have power going to the coil?

 

[alldodge]

White is full time battery power from the ignition switch. Where is the resistance wire for the run

 

[Fuss188]

Hey Kenny, I should have some time this afternoon to tinker.. I'll snap some pics of what I got so you guys can all see. Hopefully I can sneak away for a little test ride...

 

[Fuss188]

Justinshreve1986.. So you're not getting spark at all? or losing it intermittently? Either way, the engine schematic alldodge posted above is your best friend!! I figured out the wiring without any literature.. that single page would have saved me half a day! Have you tried what achris recommended in your thread? Disconnecting the interrupter switch, and tach? (one at a time) That would eliminate at least those two elements of it. I have checked my interrupter switch and it seems fine. going to check Tach today. Did you replace the rotor when you replaced the cap? Because I bought my cap and rotor at the same time and as I stated before, the new rotor was 2.5mm shorter than the original.. which I believe was doing some weird stuff inside the distributor. I cleaned up the old rotor and put it back in. Have yet to run/test the boat but I'll keep ya posted.

 

[Fuss188]

Also, Justin, to answer your question from above.. the way I understand it, with the key on you should have less than a full 12V.. like 9ish.. to the (+) side of the coil. That is 12V coming from the key switch, through the resistance wire which drops the voltage. This is one of the white wires. The other white wire should run to the starter solenoid.. so when you crank the engine, the coil should receive the full 12V to assist in starting. When the key falls back to the run position, your voltage should drop back to 9V.

 

[Fuss188]

Thanks Alldodge for the Schematic.. I ordered a shop manual but have yet to get it..

 

[nola mike]

Also, Justin, to answer your question from above.. the way I understand it, with the key on you should have less than a full 12V.. like 9ish.. to the (+) side of the coil. That is 12V coming from the key switch, through the resistance wire which drops the voltage. This is one of the white wires. The other white wire should run to the starter solenoid.. so when you crank the engine, the coil should receive the full 12V to assist in starting. When the key falls back to the run position, your voltage should drop back to 9V.

That's with the points closed. 12v if they're open.

 

[Fuss188]

UPDATE!! Ok guys, It's been a while but I finally found some time to mess with the boat. I believe I have solved the Problem! Went out Friday and Saturday with no issues! Ran great the entire time. Even got some tubing time in with the kids! So I believe the main culprit for losing spark was the fact that the new rotor I installed was about 2.5mm shorter than the original as I mentioned before. There were traces of an erratic spark inside the dist. cap and on the rotor itself. I cleaned up the old rotor and put it back on. I also checked the point gap and it was a bit wider than what I set them at last fall. So I filed the points and tightened up the gap. Pumped the gas twice and she fired right up after sitting for two weeks. Finally got to enjoy it and my kids are ecstatic! Now on to the 101 other things I want to do to it! Thanks again guys for all the help! Happy boating!