Low voltage at the coil

[Sonny]

I installed a new blue high rev box on my 440 Belvedere and the instructions say that when the key is in the run position (car off), the voltage at the coil should be 7-9 volts. I have 6.7. Is this an issue? If so, what could cause the low voltage? New stuff I added months ago: harnesses, coil, ballast resister (came with ICU), battery, 95 amp internally regulated alt (removed the VR), bypassed the ammeter, stock dizzy, installed larger alternator wire to starter relay with fuse able link. Starts, runs and drives fine.

 

[RemCharger]

Check voltage with the car a bit above idle. Sounds like youre ok

 

[451Mopar]

Your likely fine. It depends on the ignition coils resistance and the ballast resistors resistance.
With the engine not running, the Ignition box is grounding the coil negative (-), because nothing is changing (DC, not AC, and no dist signal) it is just a simple voltage divider between the ballast resistor "resistance", and the Ignition coils resistance. I would be more concerned if the voltage was higher which could be an indication of a bad ground connection at the ignition box.

 

[Sonny]

So I swapped my orange box For the blue box and it’s resistor. Went for a test drive, ran great for about a half a mile, then started missing and shaking like crazy. I limped it back home swapped out the old ballast resistor for the new, same problem. Then I put the orange box back on and it ran fine. However, now my engine off start position voltage at the coil is only 3.5 V, about 5 at idle and can rev it to 6v. I guess I just burned up a brand new $50 blue box, or maybe it didn’t have enough voltage?
Any suggestions?

 

[Bee1971]

A - What Coil Are You Using ? Brand + Primary Ohm resistance

B - Both Ballast Resistors - Measure With Your Ohm Meter (Low Setting) What Is Your Ohm Reading
Across Both Male Spades

.5 - 1.2 - .8 - 1.8 Ohms Are just some examples of Ballast Resistors

There Actually Might Bee A # Stamped On The Male Spades also

 

[Sonny]

So I swapped my orange box For the blue box and it’s resistor. Went for a test drive, ran great for about a half a mile, then started missing and shaking like crazy. I limped it back home swapped out the old ballast resistor for the new, same problem. Then I put the orange box back on and it ran fine. However, now my engine off start position voltage at the coil is only 3.5 V, about 5 at idle and can rev it to 6v. I guess I just burned up a brand new $50 blue box, or maybe it didn’t have enough voltage?
Any suggestions?

engine off, run position:

 

[Sonny]

Engine at idle:

 

[Sonny]

A - What Coil Are You Using ? Brand + Primary Ohm resistance

B - Both Ballast Resistors - Measure With Your Ohm Meter (Low Setting) What Is Your Ohm Reading
Across Both Male Spades

.5 - 1.2 - .8 - 1.8 Ohms Are just some examples of Ballast Resistors

There Actually Might Bee A # Stamped On The Male Spades also

1.2 ohms

 

[Sonny]

Also, my power probe’s + sign flashes red at idle at every terminal. Is that right?

 

[Bee1971]

I need to know what coil that is - Brand

Also take your Ohm meter - Engine off - Key off

Probes on the + and - of coil what does it read

 

[Bee1971]

6.2 Volts at idle + side of coil with that ballast is normal

Depending upon resistance of Ballast - 6 to 9 Volts running is normal

 

[Sonny]

 

[Sonny]

I need to know what coil that is - Brand

Also take your Ohm meter - Engine off - Key off

Probes on the + and - of coil what does it read

Moves from 0.6 to one with wires unhooked

 

[Sonny]

Moves from 0.6 to one with wires unhooked

Primary resistance is about 0.8 and secondary is 11,400 ohms.

 

[Sonny]

I need to know what coil that is - Brand

Also take your Ohm meter - Engine off - Key off

Probes on the + and - of coil what does it read

Jegs.

 

[Sonny]

Primary resistance is about 0.8 and secondary is 11,400 ohms.

Sounds like I have a bad coil???

 

[Sonny]

Bad coil. Boom. Fixed And runs great with the blue box and idles better too. I’m glad I chased that rabbit down that hole. Thanks for all your input.

 

[Sonny]

Bad coil. Boom. Fixed And runs great with the blue box and idles better too. I’m glad I chased that rabbit down that hole. Thanks for all your input.

Now have 8.5v at the coil.

 

[Bee1971]

Sorry

Work got the best of me - I can’t spend all day on the Computer LOL

That’s awesome - When you said 1/2 mile and your results I suspected right away

Ask me how I know

Anyways

I have been preaching that for weeks - All this Chinese crap out there and piecing together a decent system today is like

These ECUs today don’t work together with certain coils

Also that Jegs coil has interesting specs with a 1.4 Primary and 4700 Secondary

And your testing wasn’t even close to those specs

 

[Bee1971]

MSD Blaster Epoxy and an Oil filled with there .8 Resistor - Both Junk

Plus I had a Pertronix 40011 Spider Crack from the positive lead thru the tower to negative lead - NO Ballast , removed resistor and installed jumper on back side
Lasted one summer

How it didn’t leak oil is beyond me


Now I just run a cheap all the way up to 6,000 RPM all day long - Zero issues

1.2 Ohm Ballast

Hi Rev 7500 Ignition Box from Rick E