I've been using this since day one with new engine. I burn one coil per year. I have researched forever about 12v straight or through a resistor. MSD says straight 12v. They say there is no reason not to run 12v. 'It will work fine.' It does, for a year. Time to revert to the canister coil.

MSD Street Blaster TFI = 1 year of use. 'But there's no reason not to use it.' I've also tried the oem ford TFI coil. Worked for a year, more or less. TFI coils seem to be like the really hot girl. It's great when she's there. You just don't know how long she'll stay.

Having said that, it makes me wonder about the DUI's that use a TFI coil atop. (I do notice they sell replacement tfi coils for the DUI, and wonder how often they sell).

 

My basically stock 4.9L [except Duraspark conversion] has the original Ford square [TFI] coil with a MSDS box. It is on its approximately 5th year like this.

 

Thanks for the reply. So, your tfi coil came on that truck? If so, install it on an earlier engine, or one not wired oem for tfi, and tell me how long it lasts. That is the issue/ problem. Everyone says it 'should' work, but lasts for one year, so I'm converting to the old style coil. And with your msd, are you using the magnetic p/u of the duraspark, or triggering it using the white wire on the msd?

 

Have you tried a stock canister type coil like a MSD Blaster 2 or an ACCEL Super Stock Coil?

 

Harte3: In the post before yours I wrote the above.

DUI uses a single spark system with a TFI coil atop their dizzies, a copy of the GM design. And now a person can buy a knock off of that dizzy for around $170. But when the magic words are on a product, 'made in China,' I'll bet they last about 3 years. I strayed from my point. I wonder if the tfi coils do best with a single spark system, as they were designed to be run with.

 

Off topic, but how are you wiring it? Is it 12v or through the fuzed wire?

I need to wire up my dui.

 

That is how I have it wired now, although with a tfi coil. I'm about to revert to the old canister type since I am going through 1 tfi coil per year.

 

about wiring up a TFI coil..In my case for my 86, I merely used the original coil feed offered by Ford for an 86 TFI coil. It seems to be reduced in the harness actually though. I did a quick voltage check when I originally dropped in a Durspark DIZ to be fired by a standard Ford ECM box. I seem to remember the voltage to be under 12volts at the time. It is working fine...and has for about 2 years now. I think Ford may have dropped the coil voltage in some factory harnesses for the sake of universal use??...Just one man's experience.

I guess I SHOULD go out and check the next time for the record..I know a Ford TFI coil (which I like) and a duraspark ECM are not supposed to play well together but mine sure does...again with the factory 86 Bronco wiring coil feed..reader beware of this info.

As a side note..I once bought Two (2) new MSD TFI coils and one failed right out of the box (in an EECIV TFI install). I kept it as a token for while..and now only use FORD salvaged OEM TFI coils. (again..Just one man's experience)

 

JohnSmith: I suspect that is correct about Ford dropping the voltage leading into the TFI coil. I have suspected that but searched and searched and could not find an answer.

Anyway, one of the TFI's I ran was an MSD model. I called MSD and the $10 per hour tech guy said to run a full 12 volts. What that means, I suspect, is to hook it up to whatever the amount of current Ford ran to a TFI.

 

I think I have gotten that same hint from what I have read here as well. My 86 is parked for a few days while I tinker with my latest project..and 83 E150 300-6. When I fire up the Bronco I will definatley check the voltage in question for sure. I have read about the warning not to use a TFI coil with a stock Duraspark box ..and in fact I have a spare old school Ford duraspark coil should I need it but I must admit I haven't felt the need to change it yet. I WILL check this out in a few days when I rotate my 86 back into my DD.

 

My 86 has a resistor wire in the harness to drop the voltage. Looking at a wiring diagram I don't see a resistor on 87-89 models. All of the Duraspark (and points too, so far as I know) vehicles should have a resistor wire in the ignition harness to drop the voltage to ~9 volts.

Shouldn't matter with a CD box since the ignition hot voltage is basically a relay, the box runs off the battery connection once it's on.

 

AFAIK, most vehicles with a coil and distributor have some kinda resistor. Usually tied to a method of applying 12v by the starer relay (I terminal) or ignition switch when in start mode to bypass the resistor giving a hotter spark. A nice hot spark to help start the engine during low voltage conditions, such as when it's cold out and the starter is draining all the energy. The resistor also prevents the coil from over heating and reduce wear at the cap and rotor.

According to the schematic earlier in the post, it shows no resistor but I suspect it's built into the system so no worries there. If the original wire that went to the original coil is used, voltage should be around 9 volts.

Hope some of this theory helps!

 

The consensus seems to be that 9v is what Ford uses. That is where I went wrong. When I changed from 390 to 300 engine everything got rewired and the resistor got deleted. That deletion turned out to be rather expensive.

Where it became confusing or misleading was in the MSD diagram. Of course the diagram with the TFI coil shows TFI era wiring, and illustrates where to tap into it. I never took into account that Ford dropped the voltage in the oem wiring of that era. And the guy taking tech calls in his pajamas for MSD doesn't know dudally bug other than the diagrams.

That may also explain why I'm going through dizzy caps and rotors so quickly--every 90-180 days.

 

It's hard for me to 'see' whats going on here, don't know how it's wired up or where or what's changed from stock... And is why I posted the theory of the resistor wire.

If MSD runs without it then go by their engineering. If the original coil wire goes on + side of coil, then maybe consider placing the resistor wire back in.

I wanted a nice hot spark for my 4.9L and is why I ditched the whole distributor and single coil thing and went with a wasted spark setup. My '96 distributor is only to tell the computer when to fire spark and fuel and drive the oil pump. I have yet to hear it miss outside of cold weather starts.

Looks like this MSD takes the distributor signal and then sparks the coil. I wonder if there is an inexpensive system that could do this but output to a wasted spark coil setup? bypass the whole sending energy through a cap and rotor and allow the coil to discharge and charge and allow for a nice hot and fat dwell

 

I spoke with MSD again since I bought another msd blaster TFI coil. I was considering using the white wire on the msd box to trigger, and possibly installing a resistor to drop the volts to the coil, as Ford did.

The msd guy said the only way to use msd 6 series with a ds dizzy, is using the magnetic trigger wires as per the diagram earlier. He also said the blaster tfi coil is intended to get full 12v.

I mentioned that heat might have caused the first ones to fail. He said that was possible. The oem one has a huge heat sink around it. The msd does not. Before I mounted it I installed a heat shield between it and the block. I now carry the good oem one as a spare. If this fails I will try the Inferno TFI that puts out 50k volts, or just install the DUI and be done with it, and get a new performance curve while I'm at it.