Coil question
 

Guys,

New to the forum. I know these forums are a wealth of information, so I thought I'd try here first! Just bought a 98 Baja Hammer with a 7.4L (non mag)/bravo one setup. I recently had a coil failure and when I google the number on the coil (392-8055 70 1) the majority of what comes up is the number 392-8055 70A2??? Is this the same coil? For my own information, is the coil I have on my engine have an internal resistor, or external?

Thanks!!!

What ignition do you have ?

That would probably be helpful to know!
I will try to get over to the storage building in the next day or so to check.
So Mercury used more than one type in that year?

The part # is for a thunderbolt IV or V............ I've heard they have an internal resistor in them.

https://inboarengin.com/392-805570-1

If I am reading things correctly, the difference between the IV & V is the V's ability to advance/retard the ignition timing based on a knock sensor?

I was thinking about getting something with a bit hotter spark like the Pertronix 40511, but was unsure of the resistance required.

The TBIV and V ignitions (most carb engines) use a coil that , if I remember correctly, has .6ohm resistance. If you use a coil with different resistance you run a chance at frying the Thunderbolt timing module/amplifier. The OE coil does not use a resistor to step down the voltage. Just the old points type did.

98% of the computer controlled Merc engines used the ACDelco EST coil. Only a few used the Thunderbolt style. These will fire a SC engine with 7pounds boost and 5k+ rpms. It. also, is plenty fine for most marine engines that use this style coil.

The Thunderbolt V differentiates itself from the IV by using a knock sensor and a timing strategy (Mean Best Timing) in the module, vs a fixed 'curve' in the IV's module. Yes, a few V's did not use a knock sensor.

Interesting...
Pertronix does sell a .6 ohm coil.
I was initially concerned about the engines poor starting (it just kind of started by catching on a couple of cylinders then everything would start firing) but after my wife caught glimpse of the giant spark arching across the high output and the primary negative, I knew what part of the problem was. Of course not before I had to do the float of shame from the dock to the trailer because it decided it had had enough. :picard1:

Put the OE coil on it, their cheap and dont put anything on it that says MSD ( may start deteriorating )

you have to use a coil that matches the primary and secondary resistance of the OEM coil no matter if it is T bolt IV or V or the est set up. The big block Merc s Black side 454 / 502 used a est ignition set up not the same T bolt set ups.. There is couple of sources to buy the exact coil or even better but its very few sources -- Sierra is NOT one of those sources. . Way to many poor quality copies from secondary China makers.

The EST coil is a NON oil filled coil. Pertronix does not have the coil your looking for unless they added it to their line up but I doubt it.

Many Merc efi engines used the T bolt set up as well. The small blocks including many 6.2 and the 4.3

6.2 EFI as mentioned used T bolt ignition on many Merc engines. And for the record the OIL filled coil is not oil filled anymore. I have had issues with the current coil. I went back to an oil filled coil that I sourced out and have not looked back. This also includes the HP 500 carb engine T bolt ignition coil... Giving the heads up about this one..

MerCruiser MX 6.2L MPI Bravo Distributor & Ignition Components Parts

Adding some info --- Thunder bolt 4 did not use any knock sensors nor did it have the added ICM

. T bolt V used the added ICM. Also It had knock sensors --- even for carb engines, the T bolt V -- 5.7 350 CID had a knock sensor . T bolt V had MBT and ASA and ISSC and REV limiter -- some called it Over Speed control as well..

. T bolt 4 was in carb engines and T bolt V was in both carb and EFI engines.

Ayuh,..... Electricity is lazy, 'n follows the path of least resistance,.....
There's a good chance ya need a coil wire, or cap, 'n rotor, or plug wires, or spark plugs, as there's extra resistance down stream of the coil which caused the problem in the 1st place,....
You'll also need the new coil, as once it does what it's doin', it'll continue after you fix the initial problem,....

Thanks guys. I took F-2 Speedy's advice and bought a OE unit. I will probably go ahead and replace cap, rotor and wires also.

BUP,

What is wrong with the new style coil? I just bought a new OE 300-8M0079202 one to replace the 20 year old on my HP500, now I'm questioning that decision.

Shake the coil and see if you have the oil in it ? they went to an epoxy fill no more oil. engine miss fires after it gets hot. Keep in mind I quit buying them since last year and went to a sourced out oil filled coil. The quality oil filled coils lasted a long time. You have that proof as well 20 years correct . Only mount oil filled coils perfectly vertical

Test it and see --- Who knows you might have a good one or the issues were taken care of by now with the coils. I do not care I went and sourced my own instead of the average quality China sourced ones. The box will say China on it correct ??

With all that said even a broken clock WORKS GREAT TWICE A DAY.

Andover Coils by any chance ?

edit in: according to their Facebook page they went out of business several years ago and building torndown. Supposedly bought by Engineered Performance Ignition Co. but I see nothing on that. Bummer. Andover was where a lot of the good coils came from.