I have a 1985 F-150 with that I am changing from the TFI ignition to the Duraspark II system. Can I use my TFI coil in place of the stock oil-filled can coil that came with the Duraspark? Will the TFI coil overheat the Duraspark Ignition module?

 

Thread split to proper forum.

I have heard that some that tried it either burned up the coil or the module. I converted one but used the DS-II coil that performed perfectly for years. The DS-II coil and system uses a ballast resistor. My 85 already had the proper resistor in the wiring harness but it was bypassed. All I had to do was cut the bypass wire. If you don't have the ballast wire two Mopar ceramic resistors can be wired in series to provide the resistance needed. Special connectors are required when connecting to a resistor module tho. They can be obtained from an appliance service business. They use them to connect to heater elements.

 

Ford Ignition coils require 8.2 volts

I don't know about TFI coils.

If they require 12 volts you need one to handle that

 

Dennis, is the 78 F250 in the category of 8.2 volts?

If the voltage is 2 to 3 less than that will it cause the coil to get hot and stop voltage to the ignition wire for a few hours and then start working again?

 

If it is HIGHER voltage than that,. the coil heats up and can fail.

This why people have to consider their options when swapping in aftermarket ignitions.

"Heat kills coils"

Resistance creates heat.

The cycle continues.

 

hmmmmmmmmmmmm then my issue is working opposite then.

That's why I asked about the 8.2 volts being the standard. Mine is running 5 to 6 volts and the coil gets way too hot. I think it's getting hot enough it's causing it to not function but starts working again when it cools off. Eventually it will burn out I'm sure but it's in the live/die cycle right now.

So two things I have to prove out:
- is the "low" voltage condition causing the coil to overheat
- does the problem with battery drawdown have anything to do with it

Who was it said "I hate electrical"? I agree.

Thanks Dennis

 

Too low of a voltage will get the coil hot too. A coil is a special type of transformer. Whichever side of any transformer has the lower voltage will have the higher current, and whichever side has the higher voltage will have the lower current. If you have too low of a voltage on the primary side of the coil, it will pull more current. The more current is drawn through a resistance, the more heat is dissipated across the resistance. You are giving the coil less than the rated voltage, so it's drawing more than the desired current, getting hot and failing.

What you need to do is find what your coil is rated at (9V or 12V). 5 or 6V is too low for any coil, so you need to start at the source and use a voltmeter to find where that extra voltage is going.

 

I think you're right on with this. I've noticed that the battery which is new keeps loosing it's charge. "sometimes" I can see a small arc from the post to the terminal when everything is off. I haven't been able to track that down yet. It seems to come and go while I'm working on it. I've been thinking there must be a short since I replaced the module, voltage regulator, coil and alternator. Will dig deeper into a short somewhere drawing down the voltage.

Every time I check voltage drop at the battery and the coil terminals I don't see any variation. Also don't see any draw on the meter on the dash, although I don't know how much I trust the meter.

 

I re-checked the specs and the voltage value for DS II & DS III is 6-8 volts in run.

Have you done a resistance rest of the coil yet ?

http://www.fluke.com/application_not...AGID=1&SID=103


DSII Coil Test.

The Ignition coil must be diagnosed separately from the rest of the ignition system.

1) Primary resistance is measured between the two primary (low voltage) coil terminals, with the coil connector disconnected and ignition switch off. Primary resistance should be 0.3-1.0 ohms.

2) On DuraSpark ignitions, the secondary resistance is measured between the BATT and the high voltage (secondary) terminals of the ignition coil with the ignition OFF, and the wiring from the coil disconnected. Secondary resistance must be 8,000-11,500 ohms.

3) If resistance tests are ok, but the coil is still suspected, test the coil on a coil tester by following the test equipment manufacturer's instructions for a standard coil. If reading differs from the original test, check for a defective wiring harness.




TFI coil test.


We should now test the coil. Use an ohm meter and probe the resistance of the two small terminals, and you should find 0.3 to 1.0 ohm. If the resistance is not ok, it may be a bad coil. If the resistance is ok, probe one small terminal and the coil wire terminal. Resistance should be 8000 to 11,500 ohms. If the resistance is not ok, replace coil. If the resistance is ok, go to step 5.

 

Just happen to have an old Fluke 87. :-) Also have never had a clue how to use everything that thing will do. I can do these tests though.

I'll try these this weekend but I'm betting I end up repairing something in the wiring harness; like a short.

Thanks again Dennis

 

Here's another resource.

 

Nice!!!!!!