Bypassing ballast resistor?

[chaseincats]

My friend has a '75 280 that had a crane x700 spark box on it which we removed.

After reconnecting the stock ignition system we noticed the ballast resistor had been removed by the PO.  Using the 12v coil the crane module used, would connecting both power wires to the positive terminal cause any long-term damage to the stock transistor ignition module?  The car runs when wired that way.

If running it that way will cause an eventual issue on a '75, what did Datsun do to the '78 model since that was the only year that didn't use the ballast resistor?

Edited February 9, 2023 by chaseincats

[SteveJ]

The 78 TIU is current limiting. Even the 700 should have used the ballast resistor or higher impedance coil (3 ohm).

For background on current limiting: http://www.atomic4.com/dwell.htm

For the ignition system to work properly in a stock configuration for a 75, you need a ballast resistor or 3 ohm coil.

[chaseincats]

23 hours ago, chaseincats said:

My friend has a 75 280 that had a crane x700 spark box on it which we removed.

After reconnecting the stock ignition system we noticed the ballast resistor had been removed by the PO.  Using the 12v coil the crane module used, would connecting both power wires to the positive terminal cause any long-term damage to the stock transistor ignition module?  The car runs when wired that way.

Gotcha.  It seems the coil in there was ~1.5 ohms.  Could that cause any damage to the TIU or ECU?

Edited February 10, 2023 by chaseincats

[SteveJ]

I cannot confirm the effect on the life of the TIU, but the lack of current limiting and ballast results in saturation of the coil. The reduces the amount of energy that the coil can send out to the spark plug. It will probably reduce the coil life (Think insulation breakdown from the higher current.) and is more likely to leave you stranded somewhere. 

The blue wire coming off the coil and going to the TIU also branches off to go to the ECU. The ECU senses when the TIU grounds the blue wire to fire the coil. There should be very little current going through that wire, but I don't know the voltage tolerance of the ECU on that circuit.

[chaseincats]

Gotcha, we will go find a ballast resistor then and hopefully we didn't fry either the ECU or TIU

The interesting thing is the car worked perfectly with the throttlebody it had on it, but once we switched to one that didn't look like it came out of the bottom of the titanic the car refused to start, maybe we knocked something during installation

[SteveJ]

Not starting means you're missing fuel, spark (includes timing), or air (compression). Figure out which of the 3 isn't right.

[chaseincats]

1 hour ago, SteveJ said:

Not starting means you're missing fuel, spark (includes timing), or air (compression). Figure out which of the 3 isn't right.

The odd thing is there is spark and there is fuel injection pulse.  The car ran with the current timing until we changed the throttlebody so its probably that.

Edited February 10, 2023 by chaseincats

[Captain Obvious]

The original ballast resistor nominal is 1.3 Ohms . And the original coil spec is 0.5 Ohms. The total nominal resistance of the two in series is 1.8 Ohms. (Page EE-45 of the 75 FSM)

I'm thinking that with a 1.5 Ohm coil and no ballast resistor, you're very close to stock. You've just moved the resistances around.

And since everyone likes pics:

[w3wilkes]

52 minutes ago, Captain Obvious said:

The original ballast resistor nominal is 1.3 Ohms . And the original coil spec is 0.5 Ohms. The total nominal resistance of the two in series is 1.8 Ohms. (Page EE-45 of the 75 FSM)

I'm thinking that with a 1.5 Ohm coil and no ballast resistor, you're very close to stock. You've just moved the resistances around.

Is this true across the board? Would it also apply in the case of a ZX dizzy in my 12/71 Z? The place that did my change is "no more" and they didn't say what coil they used, they did remove the ballast resistor. I've been curious if I ever need a new coil.

[chaseincats]

1 hour ago, Captain Obvious said:

The original ballast resistor nominal is 1.3 Ohms . And the original coil spec is 0.5 Ohms. The total nominal resistance of the two in series is 1.8 Ohms. (Page EE-45 of the 75 FSM)

I'm thinking that with a 1.5 Ohm coil and no ballast resistor, you're very close to stock. You've just moved the resistances around.

And since everyone likes pics:

Interesting, I wonder why Datsun didn't do that from the start...

I talked to my friend with the car and he said the coil is making a high pitched noise after removing the 700 box and noticed the starter turns for a split second when the key is put in 'on' (even before the key is turned to 'start').  Both that odd side effect with the starter and the coil's high-pitched noise started after the 700 box was removed.

I'm assuming these are related somehow, any idea what could be causing this weird behavior?

[SteveJ]

I would guess that something is mis-wired.

[Mark Maras]

10 hours ago, chaseincats said:

 

 the starter turns for a split second when the key is put in 'on' (even before the key is turned to 'start').  

This part of the mystery seems like a bad ignition switch.