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Ballast resistor ratings for Mopar ECU
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Author:  Aggressive Ted [ Thu Feb 28, 2008 9:34 pm ]
Post subject:  Ballast resistor ratings for Mopar ECU
On the MOPAR ECU it looks like pin one is always getting 12 volts. With the newer style single resistor configuration it reduces the voltage to the coil in run position only. In start mode the coil gets the full 12 volts.

Question: Since the a MSD Blaster 2 can run a full 12 volts.....(it does this in the SlantSixDan's HEI configuration), why can't it run the full 12 with the MOPAR ECU?

Second question: what is the correct value of the MOPAR resistor? I have seen (tested) new ones from 1.5 ohms, 1.2 ohms, .5 ohms and .25 ohms.

I see 4.5 volts at the coil at idle and would like to see at least 6 volts.
All new wiring harness........MSD Blaster 2 coil, new 74 dizzy, etc.....

Thanks!
Author:  Joshie225 [ Thu Feb 28, 2008 11:20 pm ]
Post subject: 
The Mopar ECU isn't meant, nor is it able, to control the coil current. The ballast resistor and the coil itself determine the coil current. HEI modules control/limit coil current so they do not need a ballast resistor.

The ballast resistor value is determined by which ECU and coil is used. The lower resistance ballasts are typically only for high output coils and high current capable ECUs. The ECU/coil/ballast variations are covered in the Ignition chapter of the Mopar Engines book. Production coil with Chrome or Orange box uses .50 or .70 ohm resistor.

At idle you will see the lowest voltage at the coil and this is also the lowest demand as there is plenty of time for coil saturation. Saturation means the magnetic field is as strong as it's going to get, BTW. As the engine speed increases the ballast resistor will cool and the delivered voltage will increase. There is a trick you can do for racing. Connect a throttle switch in parallel with the ballast resistor to provide full voltage to the coil at wide open throttle.
Author:  Aggressive Ted [ Fri Feb 29, 2008 12:52 pm ]
Post subject: 
Quote:
There is a trick you can do for racing. Connect a throttle switch in parallel with the ballast resistor to provide full voltage to the coil at wide open throttle.
With this trick setup how long will the orange or chrome box hold up?
Is this a matter of seconds?
or minutes before the box melts?

Thanks,
Author:  argentina-slantsixer [ Fri Feb 29, 2008 2:40 pm ]
Post subject: 
the resistor is there so when you leave your ignition on and motor ain't running, you don't fry your coil. When the motor is running, the ECU sees full 12 v all the time. If you don't leave your ignition on without the motor running for large periods, you're safe bypassing the resistor.
Author:  Aggressive Ted [ Fri Feb 29, 2008 7:14 pm ]
Post subject: 
Thanks guys!

I will up grade from the dual resistor to a single and hopefully find one with a little lower ohm rating.

This is my situation:
During the winter months with the lights on, wiper on and blower on high the voltage stays kind of low at 600 rpm and will cause a very small stumble if I take off slowly. If I hit the pedal aggressively there is no stumble but the car wants to go sideways with the posi. So I would like to see at least 6 volts at the coil not 3 or 4 in those conditions. I would like a little more voltage for a nice smooth acceleration. After recurving the distributor the throttle is allot more sensitive and responsive making the car allot more touchy. :o
Author:  argentina-slantsixer [ Fri Feb 29, 2008 8:36 pm ]
Post subject: 
I wouldn't blame your car's condition on ignition issues, more specifically, not voltage seen by coil/ecu issue. I'd chase this: if your temp range is a little too spread, you might wanna consider upjetting during the cold months. If not, perhaps your wiring are kinda on the toast side, producing bad alt symptoms without actually having a malfunctioning alt. Using a volt tester, check how much output you get at the field connector behind your alt, then check how much does the battery actually sees. If you have a regulable voltage regulator, you want it to charge higher during cold periods, depending on your area. 13.6 steady is good for californian weather, 14.3 might be more "canadian"... ;-)

Other culprit could be this: did you actually adjusted your carb curb idle after driving with lights on for a while? maybe you adjusted everything perfectly without load and that's biting you in the a**

if you have a 4 pin module, you're actually using only one side of the dual resistor, perhaps your resistor connectors are upside down and the coil is seeing less voltage during engine off - ignition on periods.
Author:  Aggressive Ted [ Fri Feb 29, 2008 10:29 pm ]
Post subject: 
My voltage meter inside registers just under 16 volts, "with everything on as mentioned earlier" at 600 rpms it drops to 12 volts. Field shows 15.8 volts no load at 600 rpm.

If I raise the idle higher than 600 rpm, there is no problem with the stumble.

Wiring harness is new.

Curb idle may be a hair rich.

On the connectors, they are polarized and can only go on one way.

Good points though, thanks!

Just need to find a resistor with a little less resistance and I will be happy. :D
Author:  Eric W [ Sat Mar 01, 2008 12:51 am ]
Post subject: 
Have you tried running a wire from the alternator to the battery stud on the relay? I run a 10 guage wire with a fusable link from my alt. to the relay to take some of the electrical load off the ammeter. I also run the black alt wire directly through the bulkhead to the wire that goes to the ammeter and did the same with the red wire to get rid of the poor connections at the bulkhead.

I also run an MSD Blaster 2 coil, and use a .8 ohm resister. Its an MSD unit that they recommend with our ignitions.
Author:  SlantSixDan [ Tue Mar 04, 2008 9:52 am ]
Post subject: 
Image

This thread contained really good information on ballast resistance and on Holley 1920 air bleed and transfer slot mods. I've split the carb mod info into its own thread for ease of reference later on down the line. That thread is here .
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