Ryan Beckley

600 CI / Thunderbolt 4 ignition system keeps killing coils. We put coils from auto parts store and they died too. Just got new replacement Thunderbolt coils and they say "for use with external resistors" but we've never had that and it ran fine before. ANY IDEAS? THANKS!

blue thunder

The resistor is used when running points to keep them from getting burnt at idle. No points, no resistor needed. I guess I would question if you really are getting or creating bad coils. What is your diagnosis method?

BT

bowtie

You want external resister but the Merc Thunderbolt coil is supposed to have more windings to last longer. How about the cap and rotor and sensor. If the cap is green inside it makes the coil work harder to get the spark to the wires and this will shorten the coils lilfe. Tune up's once a year helps avoid all ignition problems.

Wobble

Do yo have any other wire hooked to the + side of the coil other than factory? if so, that load could be the problem.

oil filled coils should be mounted in the vertical position(stock).

MSD's epoxy filled blaster coil will work in any orientation

Dave_N

There are a few aftermarket conversion type electronic ignition systems where you still use a resistor, but those are not true HEI systems.

The Thunderbolt IV ignition module uses a reduced dwell (module on) time to limit current during low RPM operation and does not use a resistor. A coil that says "Use external resistor" is probably not the right coil for a Tbolt system.

As suggested above, a little more trouble shooting could help you make a diagnosis. How do the coils test after failure? Open windings? Shorted windings? Oil loss?

Dave

SB

iTrader: (1)

#1 causes I see are what Wobble pointed out. Oil filled canisters hate to be installed horizontally.

Also: check to make sure coil is not still powered up when ignition key is turned off. Being on 24/7 without engine running is quick path to 'death.'

Also check for arching from coil wire or coil wire tower to + or - terminal on coil.

Are you also running a CD box ? If so, the coil needs to be one that is made to be run for an amplifier. Some coils are made for points (resistors) only, some for straight twelve volts (most electronic) only , some for cd ignitions only, and then there are some that can be used in any of those applications.

cdscarab

Just got done replacing Accel coil on my motor. Ran great last year, couldn't keep the fires lit this year. Finally died 3 weekends ago. Replaced with old TBIV coil, motor fired right up dirty plugs and all. Checked with Chris Martin, he says he regularly finds dead auto coils on marine motors. Apparently the street hot rod coils aren't built for the extended run times that the Merc coil is. Its casing is much larger in diameter than the Accel coils, probably due heavier interneral components to help it cope with the added heat loads that extended run times produce. Makes sense, alot of the drag race stuff thats available for motors isn't suitable for marine use, apparently coils are one of them.