steve00

Hi all, been a while . my original coil 392-805570-1 sprang a leak oil flowing out the top hole where wire is , my question is I have a new flame thrower 2 0.6 ohm coil can I use this for my replacement , will this be ok or hurt my ignition being another type ohm , thanks

Bondo

Ayuh,..... So what motor, 'n ignition are ya workin' on,..??..??

SB

Quoting myself:

BUP

primary and secondary resistance has to match because of the sensor installed under the rotor. NO one uses that sensor period as that is a Merc made part in house. Its called ignition sensor assembly for all T bolts ign. . Also will add - you run the risk of burning out the ICM as well and that is a expensive part - Merc exclusive parts as well. T bolt V

BUP

and if you use a coil with higher resistance - you will have weak spark - the engine will run rich - poor idle and poor acceleration. The same goes for weak ignition parts and old spark plug wires, old spark plugs.

BUP

just passing along -- Many Merc efi models use the same coil and distributor and sensor under the rotor as the carb motors

Blueabyss

Whats the deal with the print on the side on this coil. What where is the external resistor ?

https://www.boats.net/product/mercur...AaAkWlEALw_wcB

SB

I did not look at link. The tb4/5 coils don’t use internal or external ohm resistors ? The module controls dwell from idle all the way to top rpm. It does this so coil won’t overheat at low speeds (why non electronic ignitions need resistors ie: to cut power enough coil won’t overheat low speeds. However this limits current / dwell for higher rpms) and can provide higher current at higher rpms where needed and coil has less time (measured in milliseconds) firing each plug so less chance to overheat.

However, all electronic ignitions are designed around their particular specific coil design specs, especially primary ohms. In Merc ‘s case with the Thunderbolt IV/V ‘s case, .6-.7 ohm primary ohm is what is required for not only best performance but also the module’s health. Lower ohm coils will let module provide more current than the module is designed for and ‘burn it out.’ Too high of primary ohm resistance eon’t hurt module, but will deliver weak spark every wear. Again, The module is designed (programmed if you will) to run a particular spec coil.

Easier to talk this out vs typing, but that’s most of it.

SB

Okay, looked at pic. The wording on the coil means it does not have an internal resistor, therefore ignitions like points that need resistors and use this coil, must use appropriate resistors.

No resistors are used for Tbolts.
If that coil is listed for Tbolts, than it is a direct install.

BUP

that boats.net LINK is a Taiwan Sierra coil. Merc coils do not have that sticker on it and NEVER did. But every Sierra coil has that exact sticker on it.. Also the current Merc coil is NOT an oil filled coil, they changed that to a epoxy coil..

I can help you with the Merc oem coil that was oil filled from the past.. I know who made them for Merc. The current NON oil filled coil from Merc in which is the only one available from them --- These comes from China. current Low budget crap as usual and I had issues with them so I seeked out the oil filled ones that Merc sold up till about 4 years ago.