tach problems/eletrical gurus needed

[F100camperspecial]

Electrical gurus needed!Updated the ignition on the F100 yesterday. The F100 has a 351M in it. The 351M had a DuraSpark ignition, now it has a DuraSpark distributor, TFI coil ('84 F250 w/460), and GM HEI 4 pin module ('77 Nova w/350). Runs better, starts better, but the the tach is acting goofy. The tach worked great with the DuraSpark. Do I need to shield the trigger wire (green wire) to the tach?

[Jake11]

Can you post a schematic of your setup? I would like to help if I can.
I have the same components to build an Ign. like yours.

Also, some older tach's won't work with transistor primary. Best to check
with the people that made the tach.

[Jake11]

Did it work with the Duraspark with a TFI coil before??
The TFI coil is as good or better than anything I've seen aftermarket.
Big time power. Ford got a little carried away with that one. I've measured output at 80,000 volts open circuit on a scope. One problem
to look to. If...... the coil wire is not perfect, it will feedback voltage into
the primary and cause problems, like blowing up your tach. Make sure
the coil wire is good!!!!! If not, you'll blow the module too.

[F100camperspecial]

Well, I don't know how to post pictures yet, but the ignition setup is simple. This setup assumes your ig is factory wired for the DuraSpark (Ford and Jeep).

Required componets are: 1) a spare shot DS module and a heat sink (junk computers work--I used the heat sink out of 90's Buick heater fan control): 2) a 4 pin HEI module (Wells DR100) --'77 Nova with 350 V-8:3) a Ford TFI coil with bracket and pigtail, '84- '93 F-series works--I used one out of '86 Lincoln: 4) dizzy cap adapter, dizzy cap, rotor, spark plugs and wire set for a '84 F250 with 460. Depending on where you mount the coil, you may need to fab a high tension coil lead.

Either gut the spare DS module and mount the HEI module to it, or use a heat sink off a computer. I used a heat sink off a 90's Buick heater fan control. Be sure to use the heat goo that came with the HEI module.

Disconnect the battery. Unbolt the DS module, but leave it hooked up. Mount coil. Wire the TFI coil same as DS. Green wire from DS module goes to negative side of coil. Red wire is hot keyed source and comes out of the ignition switch to BAT side of coil and the DS module. Run no resistors to the TFI coil.

With the HEI module mounted, unplug the DS module from your rig. Cut the pigtails off the spare DS module and plug those pigtails into your wiring loom. Run the Orange wire from the cutoff pigtail to terminal "W" of the HEI module. Run the Purple pigtail wire to terminal "G" on the HEI module. The Black pigtail wire provides ground for the HEI module (hook it to one of the mounting screws on the HEI module). The Green pigtail wire goes to terminal "C" on the HEI module. The Red pigtail wire goes terminal "B" on the HEI module. Terminals "W", "C", "B" use 1/4 " connectors, and terminal "G" uses a 3/16" connector.

Install dizzy adapter, dizzy cap and rotor, spark plugs and 8.5 mm wire set. I ran .045" gap on my plugs. Insert key, start motor , and enjoy hotter spark. Coooool!!!!! This mod works great on my '72 F100 with a 351M V-8. I used the existing DS dizzy that was on my junkyard '77 351M.

[F100camperspecial]

I forgot to mention to check out http://www.carbdford.com/tech/HEI/hei.htm to find out about the HEI/TFI conversion. Also check out the full size jeep forums. I found this stuff--I did not invent it.

[Jake11]

They used to make a filter as they called it, for tach's. That was a little
while ago. I like your homebrew setup. I was gonna use the same
components to make a killer ignition. I was not sure if the delco module
could handle the TFI coil. My plan was to rig it up, Ford mag. pickup,
Delco module, Ford TFI coil. Then run it to failure with a drill motor. Please comment.

Thank's Keith

[F100camperspecial]

The tach is a brand new Sunpro Super Tach, I have heard something about tach filters like you say. Yes, the TFI coil kicks serious butt. I have only run this thing a weekend, but it runs great. when I first fired the thing up, my buddy gets this goofy ass smile, I holler "Some@#$icth!". The thing even sounded better just idling. My buddy yells "Cooool!". I like it!

[F100camperspecial]

Yes, the tach run fine with the DuraSpark. I did not change the tach's wiring at all when I swapped in the TFI/HEI upgrade. That's why I'm wondering if the increased output of the TFI coil is bleeding into the tach trigger wire--hence the need for shielding.

[F100camperspecial]

Can anybody tell me if the '72 had a resistance wire for the points and where it's located? That maybe the source of my problem. With 14.9volts at the battery I have 11.01volts at the coil. I did not rig any resistors but that does not mean it ain't there.

[rjewkes]

the ignition w ire running to your coil has a fuseable link resistor wire attached to it under the dash.

[Ford_Doctor]

I love the idea of this setup. It is small, and can be easily hidden, unlike the bulky Duraspark unit. My only problem is having GM engineering on my Ford (almost seems counter-productive!).

As for the topic, I would definetely run a fresh wire from the ignition switch to the coil (to eliminate the resistance wire), and get the tach signal directly from the HEI module and not the coil, just to get it that much further away.

[trukcrazy]

I love the idea of this setup. It is small, and can be easily hidden, unlike the bulky Duraspark unit. My only problem is having GM engineering on my Ford (almost seems counter-productive!).

I'm with you on that.

[Jake11]

The wire running from the Ign. switch is a resistor wire. Chop it out,
or go around it. The older point setups used a 6 volt coil, and stepped
it up to 12volts for cold starting. Ford and GM used a inline resistor wire.
Chrysler used a separate resistor, usually mounted on thr firewall.

Keith

[F100camperspecial]

Thanks guys, I'll spend some quality with my truck today and rerig that coil source wire. The first thing SunPro asked was if I had too much ballast resistance--go figure heh?

[F100camperspecial]

Bypassed the resistance wire and the tach works great--woohoo!! Looked in my Ford shop manual and find the bit about replacing a shot resistance wire. Now I have full battery power both the coil and the HEI module and the tach reads like its supposed to.