123 spark issues - Alfa Romeo Bulletin Board & Forums
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post #1 of 20 (permalink) Old 06-23-2019, 07:39 PM Thread Starter
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123 spark issues

First of all let me get the frustration off my chest... AARRGGH!
I have fitted a 123 Distributor to my 1979 EURO SPEC Alfetta 2.0l. Car was running fine prior. It has Alquati Cams which are quite aggressive.
I am certain the static timing is correct. I am not getting a reliable spark. The spark is weak and only reliably goes to cylinder 1 and 4, with 2 and 3 not being there all all.
I am using the existing coil with attached Marelli Ballast resistor. Do I need to throw all that away and get a new coil?
Anyone been here before me?
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post #2 of 20 (permalink) Old 06-23-2019, 09:17 PM
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Quote:
Originally Posted by Millsy View Post
First of all let me get the frustration off my chest... AARRGGH!
I have fitted a 123 Distributor to my 1979 EURO SPEC Alfetta 2.0l. Car was running fine prior. It has Alquati Cams which are quite aggressive.
I am certain the static timing is correct. I am not getting a reliable spark. The spark is weak and only reliably goes to cylinder 1 and 4, with 2 and 3 not being there all all.
I am using the existing coil with attached Marelli Ballast resistor. Do I need to throw all that away and get a new coil?
Anyone been here before me?
I just checked, and 123's specs call for a minimum of 1.0 ohms of resistance in the primary ignition circuit. Check the resistance of your car's circuit with and without the ballast resistor---it could be that the resistance is too high (should probably be in the neighborhood of 3 ohms). Make sure the primary wiring and connections are all OK.

I would first try bypassing the ballast resistor if the coil has enough resistance by itself. If that doesn't work, you might need a new coil. Higher-energy ignition systems can expose problems that may have been masked by an old-school points system with ballast resistor . . . . .

If all is well in the primary circuit, move on to the secondary circuit and make sure cap/rotor and plug wires are OK.

Chris A: '81 GTV6 rescued from junkyard, "GT" car/'86 Porsche 944 Turbo track/street car/'73 BMW 2002tii fun street car/'74 Jensen Healey Lemons Rally car!

Last edited by cda951; 06-23-2019 at 09:27 PM.
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post #3 of 20 (permalink) Old 06-24-2019, 06:11 AM
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Assuming that you have a 123 with two wires:
The red wire should go to 12 volts and the black wire to coil -. The ballast resistor should go between 12 volts and coil +. That is how I have mine hooked up and it makes very good sparks.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #4 of 20 (permalink) Old 06-24-2019, 08:09 AM
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Do a search here on all of the other posts about trouble with the 123....
Should keep you busy for quite a while!

'64 Guilia Spider
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post #5 of 20 (permalink) Old 06-24-2019, 09:44 AM
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Coils are cheap. If there's any question, just try replacing it.

Pertronix makes a 3-Ohm Flame-thrower coil (model 40511) that works well with the 123 distributor. You can eliminate the ballast resistor if you use it, which simplifies things. $36 on Amazon.

Tom

1963 Giulia Spider (1750 engine)
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post #6 of 20 (permalink) Old 06-24-2019, 01:27 PM
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This is why you may consider the extra complexity of a ballast resistor to be worthwhile
https://www.alfabb.com/bb/forums/eng...ml#post7769394

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #7 of 20 (permalink) Old 06-24-2019, 01:54 PM
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A ballast system is really only there to provide more spark energy when starting. When you're starting the engine, the ballast resistor is bypassed and the resistance is just that of the coil, the point being you get better spark when the voltage drops from cranking. During running the ballast resistor is in series with the coil and raises the overall coil resistance to limit current. Basically you can have a low-resistance coil when starting and then not melt your points once the engine is running.

With modern electronic ignition systems like the 123 there's really no point (ha!) in using a ballast any more. The 123 can handle a coil down to 1 Ohm.

So if you really want lower primary resistance & more spark energy all the time you can just use the 1.5 Ohm Flame-Thrower (40011) without a ballast resistor. This is probably overkill for a 4-cylinder engine, though, and 123 recommends a 3-ohm coil for street applications and a 1.5 for modified high RPM 4C cars or V8s, where the coil dwell time is lower.

The 3-ohm Pertronix has worked fine for me on both Alfas I have it on with the 123, but they're both pretty stock.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #8 of 20 (permalink) Old 06-24-2019, 03:40 PM
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Quote:
A ballast system is really only there to provide more spark energy when starting.
Not so. Look at the graphs. The improvement at mid to high rpm is a result of lower inductance.

Back in the day we used ballast resistors with low resistance/low inductance coils to get more power from racing 2 stroke motorcycles.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #9 of 20 (permalink) Old 06-24-2019, 04:01 PM
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Well, you're comparing a 1.2 Ohm (coil+ballast) system to a 3.4 Ohm Bosch blue. That's what's causing the difference in coil current. It's not inductance, it's Ohms law.

Anyway, 3 Ohms works fine for a street car. If you're running high RPMs buy the 1.5.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
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post #10 of 20 (permalink) Old 06-24-2019, 05:01 PM
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Quote:
Well, you're comparing a 1.2 Ohm (coil+ballast) system to a 3.4 Ohm Bosch blue. That's what's causing the difference in coil current. It's not inductance, it's Ohms law.
Try to remember circuits 101. I taught it in tech college. Ohms law applies to dc circuits. Coil charging current is a waveform with high frequency components. Inductance resists changes in current. At low rpm resistance is the main influence on charging current and as rpm increases inductance has more influence and at high rpm inductance dominates charging current.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

Last edited by alfaparticle; 06-24-2019 at 05:09 PM.
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post #11 of 20 (permalink) Old 06-24-2019, 07:15 PM
But Mad North-Northwest
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So maybe I'm misunderstanding, but from the data I can find all the Pertronix coils (0.6, 1.5, and 3.0) have about the same inductance: ~6-6.4 mH.

Assuming a 0.6 Ohm coil and a 0.6 Ohm ballast in series for your 1.2 Ohm, the coil is only seeing 6V during running on a 12V system, right? At fixed coil inductance, you'd be way better off for both primary current and spark energy by just using the 1.5 Ohm coil and no ballast. What am I missing here?

Ignition Coil Simulation

Anyway, this is all academic given that a 3 Ohm coil with no ballast is more than sufficient for a stock Alfa 4C engine, and if that's not enough just use the 1.5 Ohm one without a ballast.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #12 of 20 (permalink) Old 06-24-2019, 08:48 PM
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Here is the theory - copied from a college lab text
Quote:
Step response
The response of a circuit to the sudden application of a constant voltage or current source is referred to as the step response of the circuit. This case presents the opposite conditions of the natural response. Now, in RL or RC circuits, the inductor or capacitor (assumed to be completely discharged) begins acquiring energy after a sudden application of an external power source. The voltages and currents that arise in the circuit under these conditions are discussed next.

Step response of an RL circuit
In an RL circuit the initial conditions to determine the step response are assumed to be Io=0. The expressions for the current in the circuit and the voltage across the inductor after the voltage source is applied are:

i(t) =VsR(1−e−t/τ) (6-7)

v(t) =Vse−t/τ

Notice that Eq. 6-7 indicates that the current increases from zero to a final value of Vs/Rat a rate determined by the time constantτ=L/R.
When the electronic switch closes at the start of the dwell cycle the current ramps up to a value determined by the coil resistance and the ramp rate is determined by the inductance. A lower resistance gives a higher final current and a lower inductance gives a faster ramp rate.
Higher resistance coils have higher inductance, roughly 1 mH per 0.1 ohm - it varies a little. A 3 ohm coil will have about twice as much inductance as a 1.5 ohm coil. If you compare a 3 ohm coil with a 1.5 ohm coil + 1.5 ohm resistor then they will both have a final current of 4 amps (for 12 volt supply) but the coil + resistor will get there in half the time.
This holds as long as the dwell time is longer than the charging time for the coil. After that the switch opens and discharges the coil. After some rpm the final current will start to decline. With a Bosch Blue coil the final current is down to 3 amps at less than 2000 rpm and it is down to about 1.5 amps at 5000 rpm.

How much is enough? For a stock engine with good AFR control the Bosch Blue is probably fine. With a hotter motor, who knows? For me installing a Blaster coil with the ballast resistor that came with it is a simple installation that is very unlikely to limit the performance of my motor.

I have a data point for definite loss of power. I have programmable ignition on my GTV6 and I can data log dwell time along with many other parameters. The engine misfires when the dwell time gets down to about 1.2 mSec.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

Last edited by alfaparticle; 06-24-2019 at 08:58 PM.
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post #13 of 20 (permalink) Old 06-24-2019, 09:37 PM
But Mad North-Northwest
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I think the thing you're missing is that if you use a ballast resistor in series, you're lowering the voltage across the coil. You're assuming 12V across the coil in both cases in your calculations, but with an inline 0.6 Ohm ballast resistor and a 0.6 Ohm coil you're only getting 6V across the coil. That's the only point of a ballast resistor: it drops the voltage at the coil.

Per the Pertronix documentation I can find the 0.6 and 1.5 Ohm coils are both 6-7 mH (0.6 Ohm is 7.2 mH and 1.5 is 6.4.) Even if that's an error and I assume the 1.5 Ohm coil is like 12 mH, you still do better with the 1.5 Ohm coil with no ballast resistor than the 0.6 Ohm coil with a 0.6 Ohm resistor. Try the simulator I linked to.

There's a reason nobody uses a ballast resistor with electronic ignition. Read the Flame Thrower coil instructions: they specifically tell you to remove or bypass the resistor when using an Ignitor system. The ballast system is only for better starting with points.

I'm gonna trust the guys at 123 Ignition and Pertronix.
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Tom

1963 Giulia Spider (1750 engine)
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post #14 of 20 (permalink) Old 06-25-2019, 06:26 AM
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Tom,
You are stuck in steady state current land. The current is dynamic as I explained above.

This coil current simulator is by the guys who created Megasquirt. Plug in some numbers and see the effect:
Ignition Coil Simulation

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #15 of 20 (permalink) Old 06-25-2019, 08:27 AM
But Mad North-Northwest
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But in your explanation above you're assuming the same coil charging voltage. That's not the case with an external resistor, right?

Ballast resistors drop the voltage at the coil. When you're cranking, the ballast resistor is out of the circuit and you see a full 12V across the coil. During running you're only seeing 6V across the coil because of the 0.6 Ohm resistor in series, and the coil will charge slower because of it.

You're also assuming that the higher ohm coils always have higher inductance. That is not the case from the MSD data. I think you're assuming they're just adding more turns to the same coil, which does not appear to be accurate.
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Tom

1963 Giulia Spider (1750 engine)
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