Ignition module failure..?

[AJ/FormS]

Resistance thru the PU varies a bit with temperature, but I typically see 300 +/-50 on a good one.

As to the ECUs, I have seen them bleeding goo all over the apron and still working just fine., as long as they are grounded back to the battery.
I have also seen the ballast resistor spitting out it's porcelain core, and still working fine. But they are sensitive to the the spade connectors building up resistance when not being tight enough. Once the voltage to the ECU drops below about 9volts, they can start acting up, altho I have witnessed them working just fine at 8 volts and idling.

 

[halifaxhops]

Another big BIG issue with pickups is the two wire connector. There is NO current through that connector, so ANY looseness or corrosion will kill off the tiny pulse signal. "Work" the connector in/ out several times to scrub the terminals clean, and "feel" for tightness. Inspect with a light/ magnifier for corrosion

Close no magnet creates a MV pulse that gets amplified in the ECU Think of a small generator. Every one thinks it is like points.

 

[67Dart273]

Close no magnet creates a MV pulse that gets amplified in the ECU Think of a small generator. Every one thinks it is like points.

I know how they work. The point is there is very little VERY little "minute" power going through the connector, and that means any corrosion in there can "kill" the signal.

 

[Moparbaker]

Sireland67; I thought these two wires & distributer got their power from the coil & the module..?

 

[sireland67]

To test the pickup in the distributor it will put out amps.

 

[Moparbaker]

Okidoki, tomorrow then... ;)

 

[92b]

Okidoki, tomorrow then... ;)

While you have the meter out set it to ohms and check the coil wire too.

 

[AJ/FormS]

Sireland67; I thought these two wires & distributer got their power from the coil & the module..?

The ECU powers up the Pick-Up just like the ballast resistor would power-up the points.... except the power is miniscule in comparison.
The PU interrupts this power, actually converts it to a signal, whenever a reluctor vane disrupts the Magnetic Field.
The ECU senses the disruption, modifies the signal,then commands a spark in response, thru a different circuit.
Both the ECU and the hi-tension coil have separate power supplies coming from the ignition switch thru different ballast resistors,that are mounted on a common porcelain block.
To do all that, the ECU case has to have a low-resistance ground back to the battery.
The Ecu gets it's power supply reduced by it's Ballaster to a different voltage than the Coil gets ballasted to. In a pinch both of those will run straight off the ignition switch, but I have no idea how long the ECU could withstand that.
Also, in a pinch, both of those will run on either side of the ballast. I have experienced a blown ECU-side ballast, and simply reversed the connector at the ballast to feed coil ballast to the ECU, and then jumpered over the bad ballast. That's how I saved another night in the Motel far away from home on a Sunday morning.
During cranking, the two ballasts are run in series to power up the ECU, and the coil receives full battery power.

I think I got that right.

 

[92b]

"During cranking, the two ballasts are run in series to power up the ECU, and the coil receives full battery power."
Re-do
I don't claim to know how this works but it seems odd that they would reduce voltage additionally by running the resistors in series for the ECU at a time when voltage is already at it's lowest point, during cranking.

 

[AJ/FormS]

"During cranking, the two ballasts are run in series to power up the ECU, and the coil receives full battery power."
Re-do
I don't claim to know how this works but it seems odd that they would reduce voltage additionally by running the resistors in series for the ECU at a time when voltage is already at it's lowest point, during cranking.

The ECU is an electrical device that only draws a certain amount of electricity. And it it was designed to be less than normal Battery voltage. Ballast resistors are current limiters, whose resistance varies with the current going thru it. These small ballasts run small changes so it's no big deal to the ECU. The circuit is designed that way to be simple and cost-effective; you know Chrysler. I mean they could have put the ballasts inside the ECU and inside the coil........ but then, when they would puke, you would get to spend bigger money replacing the more complicated parts, to replace the simple resistors, inside them.
>If your voltage regulator sticks in full-field, the alternator output will skyrocket. The ballast could see 18 to 20 volts or more on the input side. But you can think of the ballast as a cop standing there, and holding back the crowd, only letting the electrons thru at a regular pace, sufficient to supply the meager demands of the ECU. There is always more there than the ECU needs, until the battery level drops too far.


BTW
If you look down in the left hand corner on your posts, there you will see a DELETE button, beside the EDIT button. If you want to delete a post of yours hit the button and follow the directions. I use it a lot.lol.

 

[92b]

The ECU is an electrical device that only draws a certain amount of electricity. And it it was designed to be less than normal Battery voltage. Ballast resistors are current limiters, whose resistance varies with the current going thru it. These small ballasts run small changes so it's no big deal to the ECU. The circuit is designed that way to be simple and cost-effective; you know Chrysler. I mean they could have put the ballasts inside the ECU and inside the coil........ but then, when they would puke, you would get to spend bigger money replacing the more complicated parts, to replace the simple resistors, inside them.
>If your voltage regulator sticks in full-field, the alternator output will skyrocket. The ballast could see 18 to 20 volts or more on the input side. But you can think of the ballast as a cop standing there, and holding back the crowd, only letting the electrons thru at a regular pace, sufficient to supply the meager demands of the ECU. There is always more there than the ECU needs, until the battery level drops too far.


BTW
If you look down in the left hand corner on your posts, there you will see a DELETE button, beside the EDIT button. If you want to delete a post of yours hit the button and follow the directions. I use it a lot.lol.

Thanks for the explanation and tip on how to delete post.

 

[nm9stheham]

"During cranking, the two ballasts are run in series to power up the ECU, and the coil receives full battery power."
Re-do
I don't claim to know how this works but it seems odd that they would reduce voltage additionally by running the resistors in series for the ECU at a time when voltage is already at it's lowest point, during cranking.

Because it does not. When cranking, the start bypass feeds +12v to the coil + directly for extra energy and to compensate for the lower battery voltage. It feeds via the 0.5-0.6 ohm ballast to the the main power feed to the ECU, and also to the the low current input via both. See post #22 here:
Mopar electronic ignition wiring schematic question

And of course this is only for the 1-2 years that use the 2 part ballast. The transistor circuitry in the ECU is gonna work just fine with the reduced voltage. (Not guessing on that....spent 15 years designing electronics like this.)

The ballast description is accurate.. the term 'ballast' came from electrical/electronic designed starting in the 1920's for several 'approximate' forms of current regulation. (There were ballast vacuum tubes in some radio and TV electronics for example.)

 

[512Stroker]

The ECU powers up the Pick-Up just like the ballast resistor would power-up the points.... except the power is miniscule in comparison.
The PU interrupts this power, actually converts it to a signal, whenever a reluctor vane disrupts the Magnetic Field.
The ECU senses the disruption, modifies the signal,then commands a spark in response, thru a different circuit.
Both the ECU and the hi-tension coil have separate power supplies coming from the ignition switch thru different ballast resistors,that are mounted on a common porcelain block.
To do all that, the ECU case has to have a low-resistance ground back to the battery.
The Ecu gets it's power supply reduced by it's Ballaster to a different voltage than the Coil gets ballasted to. In a pinch both of those will run straight off the ignition switch, but I have no idea how long the ECU could withstand that.
Also, in a pinch, both of those will run on either side of the ballast. I have experienced a blown ECU-side ballast, and simply reversed the connector at the ballast to feed coil ballast to the ECU, and then jumpered over the bad ballast. That's how I saved another night in the Motel far away from home on a Sunday morning.
During cranking, the two ballasts are run in series to power up the ECU, and the coil receives full battery power.

I think I got that right.

AJ - We all know of the ballast resistor mounted in the ceramic block on the firewall.
Where is the other one that you spoke of located?
Or am I just confused?

 

[AJ/FormS]

AJ - We all know of the ballast resistor mounted in the ceramic block on the firewall.
Where is the other one that you spoke of located?
Or am I just confused?

They are one and the same, two resistors mounted on the same item. Flip it over and you will see them. Ok well not always, lol. The tip-off is the four connection points.

 

[nm9stheham]

AJ - We all know of the ballast resistor mounted in the ceramic block on the firewall.
Where is the other one that you spoke of located?
Or am I just confused?

There is a wider dual one with 4 connections used for 1-2 years with the true 5 pin ECU's.... where ALL 5 pins actually connect inside the ECU. Here is what that dual ballast looks like: 1972-1976 Dodge Charger Parts | MN1134 | 1972-76 Mopar Replacement Ignition Ballast Resistor - With Electronic Ignition | Classic Industries

Most are 4 pin ECU (even if the new ones have 5 pins, 1 pin is not internally connected), and they use the regular single resistor ballast. That is probably what you have 512stroker... the 4 pin ECU.

See posts 1 and 11 in the link I included above.

 

[nm9stheham]

They are one and the same, two resistors mounted on the same item. Flip it over and you will see them. Ok well not always, lol. The tip-off is the four connection points.

AJ... you must have a year car that uses the 5 pin ECU and dual ballast....or that has been wired up for it. The dual ballast system is the exception, not the rule.

 

[512Stroker]

They are one and the same, two resistors mounted on the same item. Flip it over and you will see them. Ok well not always, lol. The tip-off is the four connection points.

Got it
Only certain years, 4 connectors

 

[67Dart273]

Sireland67; I thought these two wires & distributer got their power from the coil & the module..?

No there is virtually NO power "to" the distributor. The pickup acts as tiny low power generator, think of a bicycle headlight generator. You turn the dist, the magnet passing the pickup and reluctor produces small pulses

 

[67Dart273]

They are one and the same, two resistors mounted on the same item. Flip it over and you will see them. Ok well not always, lol. The tip-off is the four connection points.

It is IMPORTANT to understand that this is TWO resistors in one "box" and they are DIFFERENT values from each other. This is why the "U" cutout at one end---it originally "keyed" the factory connectors

 

[67Dart273]

To test the pickup in the distributor it will put out amps.

No, AC volts. You spin the dist, the pickup/ reluctor will self generate about 1V AC

 

[Moparbaker]

I've pro'ly missed it in previous posts, but how do I test to see if the module is alright?
Even when starting cold the next day she quits in less time than the day before...
& all connections are cleaned & so on & there's still a fat wire direct between the module & engine.

 

[halifaxhops]

No real way to load test it without a bench ecu tester. parts stores USED to do it. I have one I would do it for you but shipping would kill it for you.

 

[nm9stheham]

I've pro'ly missed it in previous posts, but how do I test to see if the module is alright?
Even when starting cold the next day she quits in less time than the day before...
& all connections are cleaned & so on & there's still a fat wire direct between the module & engine.

'Parts substitution' is the only way for us guys 'in the field'.

Same thing for coils; you can measure their coil resistances but that is not a gurantee that the coil is not breaking down internally with high voltage.

The pickup resistance can be measured as noted and that is a pretty reliable indicator of their condition. But reportedly they sometimes fail with heat and still have good resistance cold.

Ballast resistance(s) can be measured. Should be very low. Connect your meter leads together a few times and note the average resistance of the leads alone. Then measure the ballast resistance, and subtract out the lead resistance to get an accurate ballast resistance. Should be 0.5-.06 ohm cold for the proper one. If you have a 2 part ballast, the other side should read around 5 ohms.

And it is plausible for a ballast to read OK cold but go bad when hot.

For a running test: Place a voltmeter between coil + and battery - (or a known good ground) and check that voltage with the ignition in RUN but not started, then while cranking (around 10 volts cranking), then idling after a minute (6-9 volts idling), and then when it quits. Let us know.

 

[67Dart273]

No real way to load test it without a bench ecu tester. parts stores USED to do it. I have one I would do it for you but shipping would kill it for you.

In this case a doubt any tester will show. Intermittent problems are always the worst, and many testers (generally) won't show this. Really, at this point there is only so much you can do

Make CERTAIN the module is well grounded
Make certain the harness and connectors is in good shape, and that there are no bad connections
Make certain the module and coil are getting proper voltage.

If all that is true, it's time to take a gamble. Swap out the coil if you have not done so, and if that doesn't fix it, swap the module.