Question about Duraspark 2 Ignition System

Hello, i made a short video asking for help regarding higher than wanted voltage at Ignition Coil.

Let me know your thoughts and thank you for your time.

If you want to test for the resistor wire disconnect the coil and DSII power plug.
Ohm between the coil power and the red and the white wires in the DSII plug.

How high is the truck voltage when it is running?
If the resistor is working but the alternator is putting out 15V what you see may be entirely normal.
A simple Ohms law calculation will show you that.

Jim is spot-on. You really need to measure the voltage or resistance when the engine is off.  That's because when it is running the ignition module is making and breaking the circuit several times/second.

So your meter is in DC mode and seeing a very complex signal of maybe 7 - 9 volts when the circuit is closed, then a rising voltage to something like 35 volts due to the ringing as the circuit opens, then down to battery voltage while the circuit is open.  And a DVM cannot properly "read" that.

Here's a pic from my oscilloscope of a DS-II ignition primary circuit while the engine was running.

I don't have any 'fancy' test equipment at hand, but I will say the resistor is only going to show while the coil is actively sinking current.

I hadn't really thought about ringing but it obviously there, EMI is its artefact.

With the coil and DS-II module out of the circuit, as you suggested, he should be able to measure the 1.1 ohm resistance of the wire.

As for measuring the voltage, I've often wondered if the DS-II module sinks current regardless of where the rotor is if the engine isn't turning.  In other words, as if the points were closed.  I haven't checked by bumping the starter, but every time I've put a meter on the coil it is obvious the module is sinking current.

The reluctor wheel needs to be spinning past the pickup in order to induce a trigger pulse for the transistor in the module.

So, you have your answer.

Makes sense.  Thanks.

You can check by tapping the distributor with a screwdriver handle.
That should be enough to trigger the module.

In fact this is the Ford diagnostic procedure.

With the coil and DS-II module out of the circuit, as you suggested, he should be able to measure the 1.1 ohm resistance of the wire.

As for measuring the voltage, I've often wondered if the DS-II module sinks current regardless of where the rotor is if the engine isn't turning.  In other words, as if the points were closed.  I haven't checked by bumping the starter, but every time I've put a meter on the coil it is obvious the module is sinking current.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in back, & EEC-V MAF/SEFI

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NAML

Good morning Jesse.

1.2 Ohms seems a little high (1.05-1.15 is spec) but that could be down to a little oxidation in a connector or even the leads of your meter.

Remember, you're not testing by putting any kind of real load on the system.
But you have proven that the resistance is there.

Yes, you've proven the resistance wire is in place.  And the difference between 1.1 and 1.2 ohms could be the leads, as Jim suggested, or just the difference in meters.  Low resistance like that is really hard to measure accurately.

As for the 10.5 volts you are measuring while the engine is running, I think it is a red herring.  The ringing will vary by the coil that you have and whether or not you have a condensor/capacitor snubbing it.  And different meters will probably give different readings because the chip in them computes the DC reading differently.

But I think you've answered your question - the resistance is there and your system is working correctly.

Good morning Jesse.

1.2 Ohms seems a little high (1.05-1.15 is spec) but that could be down to a little oxidation in a connector or even the leads of your meter.

Remember, you're not testing by putting any kind of real load on the system.
But you have proven that the resistance is there.

 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.

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NAML



Jim,

Yes meter was a little back and forth between 1.1 and 1.2 (after I adjusted for meter lead resistance) 

Before I close the case on this, I would like to know the best way to measure the resistance of the full circuit ignition circuit with key in run position. I’d like to do some ohms law and try to figure out how much amps is in the circuit and then contact pertronix to see how many my flamethrower coil can handle. I will say that as my engine rpms increase so does my input voltage at coil. I know the test is not going to be perfect but surely it will give me an idea and I would enjoy the exercise. 

So in your opinion, what two points should I use to make my resistance test measurement? Main battery ground and coil (+)?

Thank you,

Jesse 

On Jun 7, 2020, at 8:56 AM, ArdWrknTrk [via Bullnose Enthusiasts] <ml+[hidden email]> wrote:

Good morning Jesse.

1.2 Ohms seems a little high (1.05-1.15 is spec) but that could be down to a little oxidation in a connector or even the leads of your meter.

Remember, you're not testing by putting any kind of real load on the system.
But you have proven that the resistance is there.

 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.

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NAML

RedBull
81’ F100- 351W, C6, 9"3.00L

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NAML

ArdWrknTrk wrote

You can check by tapping the distributor with a screwdriver handle.
That should be enough to trigger the module.

In fact this is the Ford diagnostic procedure.

You are absolutely right!  I'd not ever seen that.  The EVTM says:



Sorry Gary,

You responded to me while I was typing my response to Jim. Thank you for your reaffirming I’m out as it is most valuable. 

Warm Regards,

Jesse

On Jun 7, 2020, at 9:11 AM, Jesse3877 [via Bullnose Enthusiasts] <ml+[hidden email]> wrote:



Jim,

Yes meter was a little back and forth between 1.1 and 1.2 (after I adjusted for meter lead resistance) 

Before I close the case on this, I would like to know the best way to measure the resistance of the full circuit ignition circuit with key in run position. I’d like to do some ohms law and try to figure out how much amps is in the circuit and then contact pertronix to see how many my flamethrower coil can handle. I will say that as my engine rpms increase so does my input voltage at coil. I know the test is not going to be perfect but surely it will give me an idea and I would enjoy the exercise. 

So in your opinion, what two points should I use to make my resistance test measurement? Main battery ground and coil (+)?

Thank you,

Jesse 

On Jun 7, 2020, at 8:56 AM, ArdWrknTrk [via Bullnose Enthusiasts] <ml+[hidden email]> wrote:

Good morning Jesse.

1.2 Ohms seems a little high (1.05-1.15 is spec) but that could be down to a little oxidation in a connector or even the leads of your meter.

Remember, you're not testing by putting any kind of real load on the system.
But you have proven that the resistance is there.

 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.

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NAML

RedBull
81’ F100- 351W, C6, 9"3.00L

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NAML

You can measure the current if your meter has a 10 amp or larger scale.  Just put it in series between the positive of the coil and the red/light green wire and turn the key on.  

E=IR so I=E/R.  If battery voltage is 12.6, the resistance is 1.1 and the coil is 1.5, then 12.6/2.6 = 4.9 amps.

But, I don't think you'll measure that 'cause the DS-II module has a voltage drop across it.  Assuming it is the standard .7v for a transistor then voltage = 11.9 and the current may be more like 4.6 amps.

You can measure the current if your meter has a 10 amp or larger scale.  Just put it in series between the positive of the coil and the red/light green wire and turn the key on.  

E=IR so I=E/R.  If battery voltage is 12.6, the resistance is 1.1 and the coil is 1.5, then 12.6/2.6 = 4.9 amps.

But, I don't think you'll measure that 'cause the DS-II module has a voltage drop across it.  Assuming it is the standard .7v for a transistor then voltage = 11.9 and the current may be more like 4.6 amps.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in back, & EEC-V MAF/SEFI

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NAML

Let us know what you find, please.

Let us know what you find, please.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in back, & EEC-V MAF/SEFI

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NAML

I'm very glad to hear things are working.  

You've done some good diagnosis and now have a better understanding of how your ignition system works.

You even surprised me with the 25 Ohm reading, but my '87 is wired a bit different.

If your power while cranking is running from the (I) terminal I see how that makes sense.