Mercruiser 470 blowing coils

blkzoe

Seaman
Joined
Jan 16, 2013
Messages
74
I've got an interesting problem. I've got an '86 Sea Ray Amberjack with twin FWC 170hp 470's. I swapped out the points ignition on each engine and replaced with the Pertronix II 1146a electronic ignition. Yes, I bypassed the resistance wire from the choke. Both engines run like a dream. I can make them idle at 500rpm forever. Torque during holeshot is second to none. I've even kept the cruising temps at about 170 degrees when the Bay temp is as high as 86 degrees; idling temp is at thermostat temp (160). So, what's the problem?

The port engine eats coils for breakfast. It's so bad I carry spares. Starboard? Same coil for God knows how long; no problems. So we have two engines wired exactly the same, yet the port engine destroys the ignition coil on a regular basis. I've examined the circuitry and found no shorts or obvious wiring flaws. Each coil has a 3 ohm internal resister as recommended by Petronix for 4 cylinder engines. BTW, the wiring is really low tech. See link for wiring diagram. (http://forums.iboats.com/filedata/fe...3&d=1400785086)

Here's my only hint at the cause. Right before I pulled the boat for winter I had both engines started and warm. They purred, no issues. I shift the port engine into gear and the engine stutters then dies. No restart. My first response now is to swap out the coil. Swapped coil; instant restart, engine purred.

POSSIBLE CAUSE OF COIL FAILURE(?): When shifting, could the shift interrupt (old style) cause a surge? I've read where surges can cause coil failure. Anybody else have this issue? I'm grinding my molars over this one. Any input would be appreciated.
 
Last edited:

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
Whem you remove the points system and the resistance wire you MUST use a coil that has a internal resistor
or the full 14 volts will burn up coils.
 

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
I think the 3 ohm coil is the one with the internal resistor. Stock coil is 1.5 ohm with a 1.5-1.8 resistance wire. The 1146A is designed to work with the 0.3 ohm flamethrower II coil. The Ptronix Ignitor II does change the dwell as rpm increases, could be that at higher rpm it is just drawing too much current for a stock type coil and it is overheating (just a wild guess). I would suggest going with the flamethrower II, and maybe giving Petronix support a call. My Flamethrower II (epoxy) is about 12 years old and always worked fine. Good luck.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Coil failure is usually due to excessive current. There is no way a "Surge" could cause a coil to fail unless it was a surge to many times more than 12v.

It's possible that you have a coil that is mis-marked as having an internal "resistor"
 

bman440440

Petty Officer 1st Class
Joined
Apr 4, 2011
Messages
266
swap out the pertronix module from one to the other and see if that engine starts blowing coils... if it does you know the module is bad if not you know its the wiring somewhere
 

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
A failing water cooled regulator can let the voltage output to go above 16 volts. Might use a good volt Meyer to check in the spring.
 

JustJason

Vice Admiral
Joined
Aug 27, 2007
Messages
5,319
Did you change out your cap, rotor, plugs and wires yet? If there is anything on the secondary side of the high tension system that is causing excessive resistance to current flow, be it a bad spark plug, defective cap, or a bad plug wire, the ignition coil is going to step up voltage more than it normally does in order to push through that resistance. Doing this causes the coil to draw more current than it's designed to handle. It will do it for a while, but eventually the magic smoke that makes it all work leaks out of it.
 

blkzoe

Seaman
Joined
Jan 16, 2013
Messages
74
I may have solved this riddle. This type of VR is NOT to be used with a maintenance free battery as an "over voltage" event may occur. See CDI's Installation and Troubleshooting guide for part# 194-9502. Some google research indicates as much as 19V may be produced with a maintenance free battery. An excellent way to bar-b-q your coil. I'll have to check and see what's in the battery cradle in the engine compartment.

link: http://www.cdielectronics.com/wp-con...1/194-9502.pdf
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
Another way is to attach a volt gauge to the coil positive to verify the voltage.
 

blkzoe

Seaman
Joined
Jan 16, 2013
Messages
74
Confirmed; maintenance free battery. Now I wonder if I screwed up the VR as well as bar-b-q-ing the coil.
 
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