Mopar electronic ignition ECMs: Which to consider and what to avoid!

[padam]

MSD is now owned by Holley, today most of their products are sourced from China.
In 2015 Holley bought the MSD Group, which includes brands MSD, Mr. Gasket, Accel, Superchips, Edge, Racepak, Mallory, Hays, QuickTime, and Lakewood.
My experience with present day MSD products is mixed some are more reliable than others..

Just my $0.02...

yep, it’s an issue.

Seems like Holley is leaving most of these companies to wither.

But most drag racers use them, so they have to be somewhat accountable. And new parts are at least available.

Do you think anyone other than us few gives a crap about Mopar ignition boxes?

 

[Kern Dog]

I had several OEM spec ECMs here so I cleaned them up, primed and painted them.

They all started off bare steel but I thought I’d “fancy them up” a bit.

They are not perfect but I’m okay with that.
This one is beyond help:

It has goo from another ECM that sat above it.

I’m guessing that once the goo oozes out, the reliability drops off a bit?

Here is a valid question. These originally had 5 pin terminals.

The electronic ignition conversation kits came with the 4 pin ECMS.

I thought that the conversion kits can run whether you have a 4 or 5 pin ECM. What about the cars that already came with electronic ignition that have a 4 pin ballast resistor? Will they still run with a 4 pin ECM ?

 

[Bee1971]

Post #7

Yes

All six ignition modules you have in your picture will work with a Dual Ballast Resistor
All six have real transistors

The 5 Pin ignition modules REQUIRE a dual ballast resistor in your picture

The only one that will work with a single ballast resistor is your 4 pin ignition module

All 4 pin ignition modules will work with a single ballast resistor or dual ballast resistor

 

[Kern Dog]

Post #7

Yes

All six ignition modules you have in your picture will work with a Dual Ballast Resistor
All six have real transistors

The 5 Pin ignition modules REQUIRE a dual ballast resistor in your picture

The only one that will work with a single ballast resistor is your 4 pin ignition module

All 4 pin ignition modules will work with a single ballast resistor or dual ballast resistor

I have a 5 pin Wells ECM in the car now.

I thought that with aftermarket ignition kits, the fifth pin had no wire going to it so it was redundant.
My car runs with the 5 pin units. Any idea how I got lucky with that?

 

[Kern Dog]

I don’t mean to insult anyone but this seems to indicate that there is a wire leading to the space where a pin is either there or not.

It does state that the wire is not used.

 

[Bee1971]

I have a 5 pin Wells ECM in the car now.

View attachment 1706809


I thought that with aftermarket ignition kits, the fifth pin had no wire going to it so it was redundant.
My car runs with the 5 pin units. Any idea how I got lucky with that?

You are correct

Not lucky , but manufacturers in the 80s 90s blah blah

The 5th pin is generally a dummy pin, for looks only so the customer didnt complain that the new ignition module is wrong or looks wrong or won’t work

Now personally , I don’t remember ever trying a TRUE five pin ignition module , one that requires the 5 OHM side of the dual ballast resistor

And seeing what would happen hooked up with a single ballast resistor

I don’t know if it would even start

 

[Kern Dog]

This came today......

It has some information that I already knew but there are some things in there that may help.
I was hoping to see a section showing how to test an ECM. It would be nice to be able to bench test them and throw out the bad ones.
This booklet pertains to factory 4 pin ballast systems since they were original. It also states the one side of the ballast is .5 ohms. Looking at the other lists that @HALIFAXHOPS provided, a .5 ballast resistor is commonly used:

Mine tests at .7:

This works but is it fair to say that a .5 is better, that it might allow more RPM before cutting out?

 

[RJRENTON]

I don’t mean to insult anyone but this seems to indicate that there is a wire leading to the space where a pin is either there or not.

View attachment 1706826

View attachment 1706827

View attachment 1706828

It does state that the wire is not used.

View attachment 1706829

FYI.....on the ORIGIONAL issue of the MOPAR ECU's system (approximately 1973 +/-) used the four pin ballast resistor. The resistor had two sections: one section was 0.5 ohms, used to control the coil primary current and the other section of the ballast resistor was 5.0 ohms, which applied a constant voltage to the internal components of the ECU. The wiring was "keyed" to insure correct connections. The external switching transistor switched the coil current on/off to create the spark controlled by internal components of the ECU. These internal components controlled the DWELL function (ON time of the switching transistor to charge the coil's primary winding and to determine when the spark event occured to begin the next recharge event) and to turn OFF the switching transistor to create the spark.
Later editions of MOPAR ECU redesigned the circuitry of the ECU to eliminate the need for the separate 5.0 ohm section of the ballast resistor, using just the 0.5 ohm resistor to control the coil primary current. .....ITS JUST THAT SIMPLE......
BOB RENTON

 

[Bee1971]

This came today......

View attachment 1706843

It has some information that I already knew but there are some things in there that may help.
I was hoping to see a section showing how to test an ECM. It would be nice to be able to bench test them and throw out the bad ones.
This booklet pertains to factory 4 pin ballast systems since they were original. It also states the one side of the ballast is .5 ohms. Looking at the other lists that @HALIFAXHOPS provided, a .5 ballast resistor is commonly used:

View attachment 1706845

Mine tests at .7:

View attachment 1706846

This works but is it fair to say that a .5 is better, that it might allow more RPM before cutting out?

Post #235 Hops

1974 Brain Box saves the day.

 

[MarPar]

This came today......

View attachment 1706843

It has some information that I already knew but there are some things in there that may help.
I was hoping to see a section showing how to test an ECM. It would be nice to be able to bench test them and throw out the bad ones.
This booklet pertains to factory 4 pin ballast systems since they were original. It also states the one side of the ballast is .5 ohms. Looking at the other lists that @HALIFAXHOPS provided, a .5 ballast resistor is commonly used:

View attachment 1706845

Mine tests at .7:

View attachment 1706846

This works but is it fair to say that a .5 is better, that it might allow more RPM before cutting out?

Post #235 Hops

1974 Brain Box saves the day.

@HALIFAXHOPS

Ray...

 

[Kern Dog]

Post #235 Hops

1974 Brain Box saves the day.

From post # 238:
In a nutshel the lower the ohm ballast produces more heat and increases the performance. Hence will make the ecu fail usually. They really have to be matched for the proper performance. Most of the stock black MOPAR boxes are limited to about 5500.

 

[HALIFAXHOPS]

This came today......

View attachment 1706843

It has some information that I already knew but there are some things in there that may help.
I was hoping to see a section showing how to test an ECM. It would be nice to be able to bench test them and throw out the bad ones.
This booklet pertains to factory 4 pin ballast systems since they were original. It also states the one side of the ballast is .5 ohms. Looking at the other lists that @HALIFAXHOPS provided, a .5 ballast resistor is commonly used:

View attachment 1706845

Mine tests at .7:

View attachment 1706846

This works but is it fair to say that a .5 is better, that it might allow more RPM before cutting out?

Thgey get tested hot that 7 will drop to 5. The lower the value the more RPM you will get and also more heat in the ecu which will kill it so it is a trade off. Unfortunately, that book will tell you if the ECU is bad, but no way to bench check all the internal sections of one. That is still a specialized test sen. I use a Zetron one like the parts stores used to have to test them with in the day.

 

[Kern Dog]

They get tested hot that 7 will drop to 5.

Wow...I did not know that. I appreciate the help.

The lower the value the more RPM you will get and also more heat in the ecu which will kill it so it is a trade off.

This is also news to me. This may have been common knowledge with others that I somehow never learned until now. Thank you.

The following is a Copy and Paste from Ray/HalifaxHops:
*************************************************************************************************************************
Basically the lower the ohm value the hotter the ecu gets and you will get more RPM's out of a ecu. Great example are chrome ecu's. Alot of cars run them and they are a good unit on the street you should run say .8-1.0-ohm ballast and you will get lower rpms out of it, so the heat does not build up. When racing they recommend a .25 ohm to get the max output RPM's of around 10K but they are also turned off and cooled down between runs. If you use that on the street, I will give the ecu a hour on average before it fails. Most of the new Mopar "authorized" kits with the Chinese ecu come with a 1 ohm ballast. But they seem to overheat due to the fake transistor cove and the newer style one is buried in the potting on the back so no place for the heat to escape to hence more failures. That help?

Here is a simple way to think of amperage.
A 1/4" straw and water will let the water (amps) flow a good amount (think amps)
a 1/8 straw will restrict the amount of water (amps) to the unit so less amps.

You reverse this for how ohms work .25 ohms would be the 1/4" straw less restriction more voltage, the 1/8 straw would be say the 1 ohm ballast so more restriction less voltage.

That help anyone?

​

 

[Sinitro]

Wow...I did not know that. I appreciate the help.


This is also news to me. This may have been common knowledge with others that I somehow never learned until now. Thank you.

The following is a Copy and Paste from Ray/HalifaxHops:
*************************************************************************************************************************
Basically the lower the ohm value the hotter the ecu gets and you will get more RPM's out of a ecu. Great example are chrome ecu's. Alot of cars run them and they are a good unit on the street you should run say .8-1.0-ohm ballast and you will get lower rpms out of it, so the heat does not build up. When racing they recommend a .25 ohm to get the max output RPM's of around 10K but they are also turned off and cooled down between runs. If you use that on the street, I will give the ecu a hour on average before it fails. Most of the new Mopar "authorized" kits with the Chinese ecu come with a 1 ohm ballast. But they seem to overheat due to the fake transistor cove and the newer style one is buried in the potting on the back so no place for the heat to escape to hence more failures. That help?

Here is a simple way to think of amperage.
A 1/4" straw and water will let the water (amps) flow a good amount (think amps)
a 1/8 straw will restrict the amount of water (amps) to the unit so less amps.

You reverse this for how ohms work .25 ohms would be the 1/4" straw less restriction more voltage, the 1/8 straw would be say the 1 ohm ballast so more restriction less voltage.

That help anyone?

​

As I have posted multiple times, the mopar electronic ignition system should use matched components. But a significant point not often mentioned is the build quality and reliability of these vintage mopar ignition components versus today's products. I have built a number of mopar cars using vintage mopar electronic ignition components including the 0.25 ohm ballast(P2444641), chrome box(P4120534), blaster 2 coil(P4876732), electronic distributor(P3690428).
Also below is a direct copy lift from the mopar 2009 catalog.
"Designed for high-performance street and race applications. Use 1/4-ohm ballast resistor P2444641 when used with ignition kits P3690426, P3690427, P3690428..."

These installs were done 20 years ago on a couple of my personal local mopar street cruiser and occasional races cars...
And happy to report to date no field failures. Note that for each install I did mount the ECU down on the frame rail for better air flow for cooling. I cannot comment about the build quality and reliability of later mopar ignition components but can confirm in my personal experience, that the vintage mopar components do pass the test of time using the mentioned parts. Also note I do have some spares if ever needed but to date they just stay on the shelf.

Just my $0.02...

 

[RJRENTON]

Wow...I did not know that. I appreciate the help.


This is also news to me. This may have been common knowledge with others that I somehow never learned until now. Thank you.

The following is a Copy and Paste from Ray/HalifaxHops:
*************************************************************************************************************************
Basically the lower the ohm value the hotter the ecu gets and you will get more RPM's out of a ecu. Great example are chrome ecu's. Alot of cars run them and they are a good unit on the street you should run say .8-1.0-ohm ballast and you will get lower rpms out of it, so the heat does not build up. When racing they recommend a .25 ohm to get the max output RPM's of around 10K but they are also turned off and cooled down between runs. If you use that on the street, I will give the ecu a hour on average before it fails. Most of the new Mopar "authorized" kits with the Chinese ecu come with a 1 ohm ballast. But they seem to overheat due to the fake transistor cove and the newer style one is buried in the potting on the back so no place for the heat to escape to hence more failures. That help?

Here is a simple way to think of amperage.
A 1/4" straw and water will let the water (amps) flow a good amount (think amps)
a 1/8 straw will restrict the amount of water (amps) to the unit so less amps.

You reverse this for how ohms work .25 ohms would be the 1/4" straw less restriction more voltage, the 1/8 straw would be say the 1 ohm ballast so more restriction less voltage.

That help anyone?

​

Since you're now an expert in Ohm's Law, perhaps you can simplify the fundamentals of Kirchoffs Law of circuit analysis.....here's a hint:
Kirchhoff's Rule
Kirchhoff's first rule—the junction rule. The sum of all currents entering a junction must equal the sum of all currents leaving the junction: ∑Iin=∑Iout.

• Kirchhoff's second rule—the loop rule. The algebraic sum of changes in potential around any closed circuit path (loop) must be zero: ∑V=0
  
  Kirchhoff's rules are two circuit laws based on the laws of conservation of charge and energy:
  • Kirchhoff's junction rule
    Also known as Kirchhoff's current law, this rule states that the algebraic sum of currents entering or exiting any junction in a circuit must be zero. This is a result of charge conservation.
  • Kirchhoff's loop rule
    Also known as Kirchhoff's voltage law, this rule states that the algebraic sum of voltage changes across circuit elements forming any closed loop must be zero.
    Both Ohm's law and Kirchoffs Laws go hand in hand......hope this helps with your understanding how and why things work.....
  • BOB RENTON

 

[Kern Dog]

Thank you.
I do not mean to show disrespect to those that have tried to help in the past.
I know that if I gave advice that wasn't followed, then people have failures and come to forums looking for help, I'd have trouble with keeping my cool.
Again, I claim innocence/ignorance/lucky that in many aspects of my life, I've stumbled through situations and had good luck despite the possibility that I've been doing it wrong for years.
For example...
These cars are the only ones that I own that were points ignition but converted:

The red car got the famous Mopar Performance electronic ignition conversion in late 2001. Along the way, I've had ballast resistors, coils and ECMs fail but never knew that they had to be "matched". My other Mopars either had points systems that stayed in place or factory electronic ignitions using parts commonly found in junkyards or parts stores. The red car had parts that looked sort of like the stock parts but were apparently different enough to work for awhile but fail prematurely.
I was never interested in electrical systems until the past few years. I just threw parts at the problem until it ran again but nowadays, I'm trying to learn.