Ignition Electrical Question....

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RustyRatRod

RustyRatRod

I was born on a Monday. Not last Monday.
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1964 Valiant, 225 slant 6 with Mopar style electronic ignition and Hi Rev 7500 ignition ECU. So just for kicks, I measured the ballast's resistance I've been running for a while. 1.4 ohms. Seems a little high. I had a few others and found one that's .7 ohms. I know it's splittin hairs to ask, but I'm just curious. With the 1.4 ohm I was getting 6.xx volts static to the coil with the ignition in run engine not running. Now with the .7 ohm resistor, I', getting 8.xx volts to the coil static ignition on engine not running. Could this maybe make a difference with faster startups? Not that it was slow, BUT when it's up to temp sometimes it does take a few extra seconds of spinning. I haven't driven it yet, but will tomorrow. Just kinda wondering in my twisted mind if 2 plus volts equals any extra at the plug?
 
2 volts, 1000 to 1 coil ( just a number I made up.) is 2000 volts.

2000 out of 12000 (full battery voltage)

Is 16% less spark,

could it make a difference ????

Maybe!
 
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I bet Rusty if you wet your fingers and held the end of the coil while the Mrs cranks ole Vixen over- you will get yur answer. :rofl:
 
I would run the .7. Rusty have you ever checked that rig for harness voltage drop, or measured normalized charging voltage?

Couple other things you never hear about

I don't believe in overly long harness leads to/ from the ECU, either for power pickup leads, or the coil NEG wire. And I don't believe in long coil secondary wire, either.

AND everyboy claims the coil + capacitor is "just for radio supression. I do not buy that. The coil + needs a low impedance path to promote strong spark, because when the NEG side of the coil is opened by the points/ ECU, that is when the spark is generated, and the current in that circuit must go all the way back to the battery to ground. I believe that the proper value cap at the coil+ will help that tank circulating current AKA "flywheel effect" of the pulse.


Once, I thought I was wrong, but I was only mistaken
 
67Dart273 said:
I would run the .7. Rusty have you ever checked that rig for harness voltage drop, or measured normalized charging voltage?

Couple other things you never hear about

I don't believe in overly long harness leads to/ from the ECU, either for power pickup leads, or the coil NEG wire. And I don't believe in long coil secondary wire, either.

AND everyboy claims the coil + capacitor is "just for radio supression. I do not buy that. The coil + needs a low impedance path to promote strong spark, because when the NEG side of the coil is opened by the points/ ECU, that is when the spark is generated, and the current in that circuit must go all the way back to the battery to ground. I believe that the proper value cap at the coil+ will help that tank circulating current AKA "flywheel effect" of the pulse.


Once, I thought I was wrong, but I was only mistaken
Click to expand...
I checked battery voltage VS voltage at the run side of the ballast today. Battery voltage was 12.7 and voltage at the run side of the ballast was just about exactly 1 volt less. This was static with the engine not running and the ignition in the run position.
 
67Dart273 said:
AND everyboy claims the coil + capacitor is "just for radio supression. I do not buy that
Click to expand...
The FSM begs to differ!

Screenshot_20240722-215026~2.png
 
When I installed my FBO ECU, they provided a jumper wire to bypass the Ballast resistor. Been running it that way for a few years with no issues - how does that work?
 
str12-340 said:
When I installed my FBO ECU, they provided a jumper wire to bypass the Ballast resistor. Been running it that way for a few years with no issues - how does that work?
Click to expand...
It takes the ballast out of the equation, it’s just for looks at this point.
 
str12-340 said:
. Been running it that way for a few years with no issues - how does that work
Click to expand...
Back in the day we had points.

When the points are closed and the ignition is in the run position but the engine is not running.

The coil would be cooked in short order. The ballast increases its resistance as it heats up and thus reduces the current going through the coil.

With electronic ignition there is no closed point and no cooked coils under the same condition.

That's my take!
 
I suspect there might be different wire used in BRs. Resistance wire can have neg & pos temp temp co-efficients, ie some will decrease in resistance & others will increase in resistance as they heat up. At operating temp, they will be the desired 0.5 ohms if for a Chrys coil.
 
Dana67Dart said:
Back in the day we had points.

When the points are closed and the ignition is in the run position but the engine is not running.

The coil would be cooked in short order. The ballast increases its resistance as it heats up and thus reduces the current going through the coil.

With electronic ignition there is no closed point and no cooked coils under the same condition.

That's my take!
Click to expand...
The mopar boxes all draw current just like closed points. Normal HEI does not. I forget, but I Pertronix draws current as well, with engine stopped
 
As for the ignition voltage drop, it's a lot closer together with the engine running.
 
67Dart273 said:
The mopar boxes all draw current just like closed points. Normal HEI does not. I forget, but I Pertronix draws current as well, with engine stopped
Click to expand...
Agreed, they draw current when on but they are not charging the coil the entire time unlike closed points.
 
Ok. Yall carry on without me. lol
 
Dana67Dart said:
Agreed, they draw current when on but they are not charging the coil the entire time unlike closed points.
Click to expand...
Well the draw current through the coil, what do you mean? They heat up the coil, the transistor, and the ballast.
 
Maybe I have it wrong.

But my I understand is if the key is in run but the engine is not rotating the coil will not be charging, like if the points are open.
 
Dana67Dart said:
Maybe I have it wrong.

But my I understand is if the key is in run but the engine is not rotating the coil will not be charging, like if the points are open.
Click to expand...
No, not correct. Some electronic systems such as HEI do that--turn themselves off. But many draw coil current. The oddball systems Jeep used when they first went electronic drew current, and so do Mopar. I don't remember, were Jeep Motorola or Presolite?

Also, Pertronix draws current. I shut off my old Farmall after the carb runs dry, after turning off the fuel. Been about 5 times in the last 20 years, I've forgotten to turn off the key. The coil WILL be warm!!!

My cousin had a ?70's? Wagoneer, came into the store one day, wanted "another one of those black boxes." And asked me "do I have any idea why it keeps eating them?

I says, "I wasn't aware you had needed them?" and he replied, "I usually took it to Don Ba**** shop."

I says "are the kids leaving the key on playing the radio?"

And he gets this dumb look on his face, it turns out HE did not know the difference between "run" and "accessory."
 
RustyRatRod said:
I checked battery voltage VS voltage at the run side of the ballast today. Battery voltage was 12.7 and voltage at the run side of the ballast was just about exactly 1 volt less. This was static with the engine not running and the ignition in the run position.
Click to expand...
Voltage drop due to resistance in the wires going both ways through the firewall, the contacts in the ignition switch, the bulkhead and ignition switch connectors, and the Main Weld in the dashboard wiring harness. If you want rid of that volt drop, put in an ignition relay. Overspecify it, buy a dependable brand, and toss a spare in the glovebox.

Also, it's a nice gesture every now and then to wave a menu near the suppression capacitor on the coil +, of imaginary other jobs it might like to try thinking about doing.
 
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