Duraspark (1?) with TFI style coil

[brianstrange]

So the PO upgraded my 68 to Duraspark and 5.0 mustang TFI coil, and I think it's a Duraspark 1. They connected both the duraspark and the coil to the resistance wire from the engine harness. It runs as is, but I'm re-wiring everything, so I wanted to know if I'm better off running everything off 12 volts. This is my Duraspark

 

[DirtDonk]

Well, wait for Viper or Steve or one of the others to verify, but I would say your setup would benefit from the full 12v.
The Blue Grommet box you have should be able to handle it, and the coil certainly should. I just don't know how they react together. There are others using the TFI coils with their Duraspark setups too, so maybe they'll pop in and let you know what voltage they're running.

I always use 12v when it's compatible, so hopefully yours is and you won't have to rely on the resistor wire any longer.

Paul

 

[Steve83]

I'd go by the color of the grommet. If the module is built for 12V, then give it that. If not; don't. Look at zones 6F & 6G of this diagram:



The later E-core coil is certainly built to run on 12V, but it has to pass through the module (on Gn/Y to Bk/Gn), so the module is the limiting factor.

 

[Viperwolf1]

Duraspark always used an ignition resistor but lots of people have eliminated them without problems.

 

[bteutsch]

I fried two modules with the blue relief thinking Duraspark would run on full 12 volts, the Duraspark ii is what I recently installed. It definitely won't work on full 12 volts. It will work fine with the resistor wire.

 

[brianstrange]

I'm wondering if the mixed results have a connection between regular and solid state voltage regulator. My buddy fried two, and then he changes his voltage regulator to SS, and it's been fine since.

 

[Crush]

I just hooked my tfi coil up like the old round one and it is working fine for now. No long term tests yet though

 

[bteutsch]

Im using the newer style external voltage regulator. I think some versions of Duraspark can't take a full 12 volts. I wanted to use a full 12 volts, because my coil is rated for it. I thought it would gain maybe a better spark with the extra voltage. I wasn't able to make it work on 12 volts without frying the Duraspark module. If you could separate the power to the coil from the Duraspark module. I feel like that could be an option. I tried just hooking up the resistor wire to the module and full 12 volts to the coil. Only to find out from Viperwolf after I fried a second box, that the factory resistor wire actually carries full 12 volts until it gets a significant load. I was also told by someone else that all a coil does is step up voltage, so as long as it gets one volt in, 40,000 volts come out. I don't know if that's true but it made me not worry so much about how many volts the coil is getting. Plus it runs fine like it is.

 

[ntsqd]

I've run the blue strain relief Dura-Spark module both ways over many years each and never had a problem with either method.

As far as coils go, the '66 Econoline used the OEM yellow top coil; the '67 Ranchero first used the OE yellow top and then later a TFI coil. I've never driven the Bronc-up on anything other than a TFI coil.

 

[Steve83]

I was also told by someone else that all a coil does is step up voltage, so as long as it gets one volt in, 40,000 volts come out. I don't know if that's true...

It's not. The ignition coil is actually a transformer working as a simple Tesla coil. It MULTIPLIES the input voltage based on the relative number of windings. If the primary (input, 12V) winding has 100 wraps, and the secondary (output) has 200,000, then the output will be <2,000x the input (depending on many other factors, including frequency & efficiency). Put in 12V; get out ~22,000V. Put in 1V; get out ~1500V.

 

[ntsqd]

He was close though. The beginning of the input/output voltage relationship of a coil is it's "Turns Ratio", how input turns ("wraps" or coils) vs. how many output turns. A ideal 10:1 coil will output 10 times the input voltage, an ideal 100:1 coil will output 100 times the input voltage. Then the various inefficiency factors that steve83 mentions start affecting (lowering) the true output. A coil is a seemingly simple thing, but balancing all of those inefficiency factors to get the best output for the application is not a simple thing.

 

[DirtDonk]

The first two Blue grommet boxes I bought were the 19 buck cheapies. Both failed within about a week. I then bought a 100 buck box and ran with the same wires and power sources and it ran for 20 years.

Most of my diagrams show full power to the modules (no matter what color) and the resistors only to the ignition coil. I think I remember a diagram somewhere that showed a resistor inline with the module on one particular model, but none of the current ones I have show this as the case.

Paul

 

[bteutsch]

Well hopefully the 8-10 resisted volts I've got going to my coil are at least adequate for good spark. I upgraded to Duraspark from a points harness, so I didn't have a 12v wire that wasn't resisted coming from the key switch. I ran a new 16ga wire from the key switch to a relay under the the hood. That's the wire I tried using for power to the coil, as well as power to the Duraspark module. The Duraspark module I burned up first was a Motorcraft box that cost around $60.00, then I got the bright idea to run the coil off the relay and use the factory resistor wire to power the Duraspark module. That's when I burned up a replacement box that cost around $30, but was the only one available at the time. (Per Viperwolf the resistor wire has 12v until it gets a significant load) Since then I just hooked up the resisted wire back to the coil positive, and also the Duraspark module to the coil positive and it lives and runs. The newest module is a Motorcraft and I bought a spare that's a Napa escelon I can't afford to keep burning up modules so I was happy with it at least running. Runs fine so I figured I finally got it right. The coil I have is the pertronix iii blaster. My conclusion without further testing is the module can't take 12v.

 

[savage]

I just converted my 74 to the blue box and made a new harness for it, the box is using 12 volts and the coil runs off the ballast resistor, at start up it runs full 12 volts to the coil, then once running it nocks it down to 10 volts. Here, my thread on it http://classicbroncos.com/forums/showthread.php?t=258904

 

[DirtDonk]

...12v to the coil, as well as power to the Duraspark module... burned up

...12v to run the coil and use the factory resistor wire to power the Duraspark module... burned up

...resisted wire back to the coil positive, and also the Duraspark module to the coil positive and it lives and runs.

...My conclusion without further testing is the module can't take 12v.

But in your case it couldn't take even the 8-10 of the resistor wire when the coil still had 12v. Doesn't look like you tried 12v to the module only.
I'm not suggesting you try to burn up another module of course;D, but there was definitely one key test left out of your equation.

I still don't understand all about how a coil effects a control module upstream of it, the only function of which is to trigger the grounding of the coil, but perhaps that ultra low resistance in the coil itself was part of the cause of the module failure? There is even a stipulation on the II that it's not compatible with Duraspark ignitions for some reason.
I'd have to let Viper weigh in on that, as I don't get what the deal is in that regard.

And interestingly enough, that Flamethrower III coil you're using is recommended by the manufacturer to only be used with the full 12v and an Ignitor III module, so perhaps that super low internal resistance (.32 ohms) is part of the issue?

Paul

 

[bteutsch]

Savage thanks for the link. I'll check it out. Paul I'm willing to try some testing. I actually made some jumpers with a fuse holder just for that purpose. I also may should mention. The wire that powers my relay has a glass 10amp fuse in it. It was blowing and probably trying to tell me something prior to me smoking the first box. It was blowing the fuse as soon as I cranked the engine over. I increased the size of the fuse to I think 20 amps. The engine cranked and ran I think for about a minute or two and then that's when the first box died. I'm only using that relay now for power to my FITECH keyed switch wire. No problems like that. The relay I have is a NAPA one that has 2 poles that are hot when key on and while cranking. The Duraspark harness I used came from a ford f100 with the blue relief box from a junkyard. I actually scored two of those harnesses for under 20$ just used the one that looked the best. Both are the same.

 

[DirtDonk]

Nice score on the harnesses. But unless there's some hidden "partial short-circuit" that is causing things to draw more current than expected, blowing 10 amp fuses seems suspect for sure!
I guess I really dunno for sure though. Not sure how much current a Duraspark is expected to use to do it's job, but while it seems 10 or so might be reasonable, blowing the fuses that quickly seems odd. I'm guessing most of that was the low-resistance coil? Maybe that's the extra that we're seeing here.
Seems like the ICM itself would only need a couple of amps at the most.

Sure be interesting to find out what's going on. Even though they didn't say it specifically, I wonder if Pertronix considers that coil to be incompatible with Duraspark, just like they say with the Flamethrower II coils. If I find out that's the case, I'll make sure we add that tidbit (kind of an important tidbit!) to our web pages. I used their own info to populate the text sections of our site with regard to the coils using info available just last year from them, so thought it was as up-to-date as possible.

Might also be worth a call to them if you have a chance. Before just sacrificing another module in the pursuit of Bronco-knowledge.

Paul

 

[ntsqd]

Those wires in and out of the module aren't sized for a large load. I've been thinking the same thing, there's a problem in the wiring somewhere or that coil isn't compatible. If you've got one I'd put any Ford OEM coil on in it's place and try that. I realize there's $$ invested in that aftermarket coil, but I just don't see any advantage and if it is the cause of the problems then it needs to go anyway.

 

[bteutsch]

Sounds reasonable guys, Its running fine now with the resistor wire powering the module and the coil. I suppose I could pick up a different coil and give it a try. Are there any coils ford used that could use 12v? Or should I hook up an OEM coil on resisted voltage and try to power the box from 12v at the relay? The Pertronix III coil was about $35, no major loss.

 

[ntsqd]

Well, like I've posted previously, I've run the TFI "E-core" coil direct on 12 VDC on two different vehicles. My '67 Ranchero got one in about '96 (car was sold in '98) and the Bronc-up got one when I got it. Bronc-up doesn't have that many miles on it yet, but the Ranchero was my DD and saw many towing miles (<- avatar) and long distance drives to school (497 miles one-way) w/o any trouble.

Those look like this:

Grab the connector too!