1979 Dodge truck with stock ignition system. 1979 factory service manual says coil side of the dual ballast resistor should be 0.5-0.6 ohms. My resistor measures 1.4 ohms. Could this be a problem? Low coil voltage?
Correct ballast resistor
- Thread starter Earlie A
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67Dart273
Well-Known Member
You sure you are measuring the correct side, or that it is connected correctly? The dual ballast has a "U" hape opening on one end. This is to "key" the OEM harness connectors sot that it cannot be connected wrong Over the years, that "key" can break, or the connector get damaged, replaced by generic crimp on "flag" push on connectors, etc
Below is a generic, simplified diagram. Notice the "U" at the very bottom of the ballast depiction. Note that as it is viewed in this position, the bottom right terminal goes to the coil. Key switched "run" 12V power comes in, jumpered across both of the top terminals, which are near the enclosed oblong cutout in the ballast.
Below is a generic, simplified diagram. Notice the "U" at the very bottom of the ballast depiction. Note that as it is viewed in this position, the bottom right terminal goes to the coil. Key switched "run" 12V power comes in, jumpered across both of the top terminals, which are near the enclosed oblong cutout in the ballast.
Other side measures 5.4 ohms.
PRH
Well-Known Member
Are you still running a 5-pin control unit?
Many replacements are 4 pin, which don’t need the dual ballast resistor.
Time for another anecdotal story……
Before I installed and MSD ignition in my car I was running some factory 5 pin ecu and wiring I had removed from a car at the bone yard.
I had been using it for years, never an issue.
I had installed a high revving 340 in the car which had an intermittent ignition miss at high rpm.
This was over 6700, which was higher than any other engine I’d had in the car.
When the 340 went in, I also used an MSD Blaster coil, which I had mounted on the intake manifold.
Previously I had always used the big yellow Accel super coil.
Swapping back to the super coil showed improvement, but did not eliminate the miss.
I checked the voltage at the coil with the engine running…….about 3 volts.
“Ah hah”
So I started probing the wires……..the closer I got to the firewall connector the higher the voltage, but even right at the connector, the wire feeding the ignition was only like 11 volts.
I peeled some insulation back, and the copper strands were all green.
I already had an MSD 6 on hand, and since the main power feeds for that bypass all the factory wiring, I installed it.
Problems gone.
7500 miss-free rpm.
That’s the long way to say, I’d suggest checking the voltage at the coil with the vehicle running.
If it has the correct style coil, and the voltage is between 6-9 volts, I think you’re fine.
Many replacements are 4 pin, which don’t need the dual ballast resistor.
Time for another anecdotal story……
Before I installed and MSD ignition in my car I was running some factory 5 pin ecu and wiring I had removed from a car at the bone yard.
I had been using it for years, never an issue.
I had installed a high revving 340 in the car which had an intermittent ignition miss at high rpm.
This was over 6700, which was higher than any other engine I’d had in the car.
When the 340 went in, I also used an MSD Blaster coil, which I had mounted on the intake manifold.
Previously I had always used the big yellow Accel super coil.
Swapping back to the super coil showed improvement, but did not eliminate the miss.
I checked the voltage at the coil with the engine running…….about 3 volts.
“Ah hah”
So I started probing the wires……..the closer I got to the firewall connector the higher the voltage, but even right at the connector, the wire feeding the ignition was only like 11 volts.
I peeled some insulation back, and the copper strands were all green.
I already had an MSD 6 on hand, and since the main power feeds for that bypass all the factory wiring, I installed it.
Problems gone.
7500 miss-free rpm.
That’s the long way to say, I’d suggest checking the voltage at the coil with the vehicle running.
If it has the correct style coil, and the voltage is between 6-9 volts, I think you’re fine.
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PRH
Well-Known Member
The “other side” of the dual BR goes to the 5th pin.
No 5th pin…….use a single BR.
I believe the MSD BR is about .8 ohms.
No 5th pin…….use a single BR.
I believe the MSD BR is about .8 ohms.
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The way I read my electrical diagram it would be the 5.4 ohm side that is not needed. I still need the 0.5 ohm side for the coil. I’ve been running a 1.4 ohm resistor instead of the 0.5. Could that cause problems?
PRH
Well-Known Member
“Problems”?
Probably not durability problems, but more resistance in the feed to the coil should result in lower voltage output.
How much lower is the voltage at the coil with a 1.4 ohm resistor vs a .5 resistor?
And how would that impact output voltage?
I can’t answer that.
Probably not durability problems, but more resistance in the feed to the coil should result in lower voltage output.
How much lower is the voltage at the coil with a 1.4 ohm resistor vs a .5 resistor?
And how would that impact output voltage?
I can’t answer that.
67Dart273
Well-Known Member
Correct, what I was attempting to point out. The coil side is the lower resistance. Maybe a high speed miss with more resistance. Look up your coil specs. The coil/ resistor specs, over the years are in the back end of chapter 8 in the manuals. You can download them free, from MyMopar.com. Several of them got them because of some of the guys right here
The motor is a turd at low rpm, but that is most likely due to low compression and a 300 duration cam installed 5 degrees retarded. The motor starts pulling OK around 2500-3000 rpm but does have a surging/missing issue. That’s what I’m chasing.
Ant
Well-Known Member
With the key in run with the engine off, measure the voltage at the coil. It should be in the ballpark of 6-7 or so volts.
Give all the details of what you have done to the motor and the full cam specs.
I have a four pin here that measures identical to what yours did. 5.4 on one side and 1.4 on the other. I threw it back in the box and went with one that was .7 ohms.
Ever try to run the 1.4?
I HAD a 1.4 two pin ballast on it for like the past two and a half years and didn't know it. I just replaced it with a .7 two pin a few days ago. It ran fine with the 1.4. I can't really tell a difference with the .7. Not that I thought there would be. It's closer to the .5 that Mopar says the electronic ignition should have, so I put it on.
PRH
Well-Known Member
Frankly, I’m surprised you’re trying to chase down a potential ignition issue, when by your own measurements you have a camshaft with an exhaust lobe that’s missing .035” worth of lift.
I have some elec psychosis going on with our car. So I've been researching ballasts/coils etc. RU11 or an RU19 is spec's for .50-.70 ohm and is 2 post.
Good luck.
Good luck.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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300 degrees at what tappet lift. SAE at .001 valve-lift, 300 is nothing, that could be 268@ .008 tappet lift
But why in 'ells name is it in 5* retarded. I would fix that ASAP. and in a smogger compression ratio engine, I would advance the crap out of it.
Here's a secret;
I have run the Mopar ECU and a standard Mopar coil on full battery voltage, for several hours during testing. My world did not end and nothing blew up.
YOUR results may vary.
300 is at 0.006. I bought the truck this way. Had been sitting for 10-12 years. Cam swap is in the near future, I hope.
Ant
Well-Known Member
Yup
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