• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

what keeps killing ignition boxes

Just curious what kind/size altenator are you running? I suspect a volatage spike.
I don't know if it would work here but we ran into a problem years ago with some controllers frying over and over, never could figure the cause but I ended up installing MOV's on the line voltage coming in( 10-30v) and it fixed the problem. They are cheap and can be had at any electronics type retailer...
 
I have no problems running my Rev-N-Nator ECU with a 0.8ohm ballast resistor and electronic voltage regulator with an MSD Blaster coil.
Also using ATL-86 plugs and 7mm ignition leads....nothing fancy and it runs well.
 
There is a SAE spec for load dump. It's a 70V spike that decades 250ms. In theroy this happens when mechanical voltage regulators are slow to react to large load changes. I have been told that the occurrence is extremely rare.
 
JimKueneman said:
That is for a constant power load. This is not it is a voltage source clamped across an inductor (coil). V=L*dI/dt. Where V, L and dt (at a given RPM) are constant. So the peak I is equal to V/L*dt. The resistance will drop some of the 12V across it so the peak I in the inductor will be smaller because the L does not see as much V across it.

Put the resistor in the circuit here and do the math. Peak Current is smaller.

https://www.ratwell.com/mirror/users.mrbean.net.au/~rover/ketterin.htm
Click to expand...
Thats buyable on an old point system but thats not what we are working with. No point arch in a magnetic pulse trigger with no mechanical parts other than the shaft supporting the reluctor. If that were the case the air gap would have to be figured into the electrical load. That would also put the secondary system components into the picture.
Find it hard to believe spark plugs, wires, cap, rotor and distributor cap to rotor air gap could be responsible for taking down the ecu.
But basically that would be part of the coil load on the secondary circuit. Load on the secondary circuit has always been determined in the combustion chamber and not by total coil output. The spark plug only uses what emergy that is required to fire it. So if the plug constantly needs 40000 v to fire will that take the ecu down?
 
mopar 3 B said:
Thats buyable on an old point system but thats not what we are working with. No point arch in a magnetic pulse trigger with no mechanical parts other than the shaft supporting the reluctor. If that were the case the air gap would have to be figured into the electrical load. That would also put the secondary system components into the picture.
Find it hard to believe spark plugs, wires, cap, rotor and distributor cap to rotor air gap could be responsible for taking down the ecu.
But basically that would be part of the coil load on the secondary circuit. Load on the secondary circuit has always been determined in the combustion chamber and not by total coil output. The spark plug only uses what emergy that is required to fire it. So if the plug constantly needs 40000 v to fire will that take the ecu down?
Click to expand...

The solid state ECUs just replace the points with a BJT or FET device. It is the same analysis. The failure modes are numerous on the solid state device but they all boil down to too much current, too much voltage, too much power or the combination of current/voltage during the switch transition (mostly a BJT problem with secondary breakdown which the original orange box Mopar boxes were I am told). If the secondary path takes excessive voltage to break down (excessive meaning more than the system was designed for) that would probably end up being the coil winding insulation breaking down and arcing over internally or the voltage on the ECU switch ringing to a point where it is too high and breaks down and fails. It is very, very difficult to say what is happening without a scope on the coil terminal (or capacitively coupled to a spark plug wire) and a current probe on the primary.
 
Last edited:
Point is. As long as providing sufficient ecu grounding prolongs the life of the std ecu that is what i will continue to do. Have had insignificant ecu losses with this method regardless the coil used.
 
mopar 3 B said:
Point is. As long as providing sufficient ecu grounding prolongs the life of the std ecu that is what i will continue to do. Have had insignificant ecu losses with this method regardless the coil used.
Click to expand...

Agree good grounding is imperative to any electrical circuit. What a circuit does starts to get unpredictable with bad grounds. Currents can go places they never normally would and cause all sorts of havoc.
 
magvan said:
In 2 of my mopars i keep going through ignition boxes.
in my coronet they work for awhile and then all of a sudden they seem to randomly get hot and turn off. let them cool off and drive it home usually with them dieing a couple more times on the way. i think im on the 3rd or 4th box this car has also killed about 5 ballast resistors, 1 distributor pick up, and a pertronix. i have just recently switched to an HEI module on this car, so ill see what happens

my pick up has been fine for about a year and a half but now last week the truck was running wednesday when i parked it and on saturday, no spark the box is completely dead. replaced the box and it fired right up and has been fine until this morning, i get a block from my house and died, walked home got another box and tools, changed out the box and fires right up. think this is the 4th box on the truck now. when i bought it the box was dead

i have used military surplus boxes, mopar orange box, standard chrome box, even tried no name box. all of them were/are made in the USA boxes
Click to expand...

The hardest thing on those ignitions is having the ignition in the "Run" position with the engine not running. Don't use the "Run" position to sit and listen to the radio, use the "ACC" position. Reason is, with no signal from the pickup, the ECU transistor is on (or closed) to charge the ignition coil, so you have constant current through the ballast resistor, ignition coil, and the ECU. With a constant (non changing) load on the coil, it puts the maximum current through the circuit, and will generate the greatest heat.
When the ECU detects a signal from the pickup, then it opens the circuit for a fixed dwell time to create the secondary ignition spark (through the collapse of the magnetic field in the coil.) When the car is running, the constant charge/discharge of the ignition coil limits the current in the primary ignition circuit, so the electronics run cooler when the engine is running.
Other problems are how the ECU is grounded through the body, while sensing the signal from the dist in the engine block. If you have bad ground connections, especially from battery to engine block, when cranking the engine (High current load from engine (starter) to battery, The voltage (Current * resistance) created in the battery ground can create a ground loop effect where the pickup signal "ground" reference voltage is offset from that the ECU sees as ground. I haven't checked an ignition pickup to see how much isolation it has from the ground?
 
Not having enough current to the component can fry them too. I killed a couple of fuel pumps finding that one out. Add in the old car poor grounds, old wiring, voltage drops due to bad connections and you have component killers.
 
Thats why I say, need a good powerplant for it ( good alt ). There is where stock alts with poor iddle output kills them too
 
This is just my thought on any voltage issues with our old cars. A built BB or RB requires at least a 850 amp battery to guarantee it to start hot or cold. To biggest drain with factory equipment was lights, heating and cooling.
I have had 900 amp batteries start the car on below freezing days after leaving the lights on for hours.
If voltage from the same battery is dropping to dangerous levels at a stop light reguardless the charging system there is a serious problem some where.
 
Sorry ive been in the middle if nowhere for the past 3 days.

I have a stock mopar 65 amp alternator on the truck.
the coronet also has a squareback alternator with electronic early looking regulator.

Both cars have clean bare metal where the ecu bolts are. Truck has factory bolts with the paint cutting washers, coronet has star washers to bite into the metal.

To be clear, the coronet the units get hot and shut off and will restart after it cools off, sometimes it'll last 5 minutes and sometimes it'll last two days before it dies again, this has only been a problen for the last few years.

The truck straight out kills the box dead. This is been a problem for the last week and a half the last two years it has been fine.

As for coils the truck has an MSD blaster been on there ever since I bought it and Its been on there years before I bought it.

The Coronet has a crane ps50 coil the same coil I run on all of my other Mopars with electronic ignition, and the same coil I ran on all of my Ford's that I ran Mopar boxes on.
 
What are the voltages while running? You need to be sure the regulators are managing the voltage within tolerance. The ecu is often the weakest link with voltage spikes. Too much voltage=too much current=overheating and failure.
Otherwise, a missmatch of ecu, coil and balast resistor can cause too much current through the ecu which can also cause it to overheat.
Are the ground straps from block to firewall intact, tight and free of corrosion? Sometimes the corrosion is under the insulation. A jumper from the ecu to battery neg can help to verify if grounding is the issue. The bad grounding causes a drop in voltage where the ecu may not operate properly and some internal components can overheat due to unstable voltage and current flowing in the wrong paths for longer than designed
Note that current in the circuit to the coil, etc, will not increase if the voltage drops. If the resistance remains the same (coil and ballast resistor), current will drop if voltage drops as per ohms law. This will cause havoc with the components involved. First thing to do is test the voltage before and while running. Particularly when you find the ecu running hot.
 
Last edited:
I haven't used a Mopar/stock ECU since the early 1990s. I heard the quality really got bad after that?
I never had issues with voltage spikes, just the grounding problem.
Back in the 1970s-1980s the Mopar Electronic conversion kits were really inexpensive, I think in the late 1970,s they were around $60-$70, then my the late 1980, they were around $100. Now they want crazy prices for what is almost the same as a stock 1970s ignition system.
Now days there are more (and better/less expensive) options than giving yourself headaches with the old style system.
 
Didn't read this whole thread but make sure if your running any type electronic ignition that you are not running the old mechanical voltage regulator. The regulator must be an electronic unit that supplies constant voltage.
 
I have read some of the replies, and even I'm familiar with elect language, I'm not really INTO that world. However I have to say that the coil and ECU setup hasn't to be SO CRITICAL to get constant fails when any unknownledgement guy can match any setup.

Msd Blaster coils and many others are designed to be used in stock ign system without overthink about that, just to get easy and cheap more juice from the ign system. Same about ECUs.

Can you get better juice working on match the best as posible all the related parts? True, but that doesn't put restrictions on any use as a replacement part for stock systems.

Same applies when using a "regular" performance ECU. MP for example sold their units as a single unit and not in combo and nowhere says it MUST be used with X or Y to save from failures.

Is simply like this.... we are getting poor quality products with smaller room tolerances to diff setups.
 
Running volts at battery 13.5
Running volts at alternator 13.7
Running volts at ballast resistor 13.4

I also just measured voltage at the ignition box connector terminal 1,2,3 as per mopar service manual. And were all less than 1/2 volt from battery voltage
 
Last edited:
that sounds a bit on the high side to me. I'm usually looking for about 13.5-14v. I suspect that when a load is applied such as the headlights, the voltage spikes higher which causes the current to rise as well. That'll blow the ecu and ballast if it goes high enough.

what is the resistance (ohms) of the coil? disconnect the wires and measure the primary + & - terminals.
 
Last edited:
You must log in or register to reply here.

Similar threads

M
Msd 5 box with stock electronic distributor
Replies
14
Views
1K
Ceedawg
C
Kern Dog
How to test ignition components.
3 4 5
Replies
80
Views
5K
RJRENTON
RJRENTON
theamcguy
How good is the Proform 440-425 ignition box
Replies
4
Views
2K
Bird 426
Bird 426
devinism
1964 Steering coupler, manual. Size difference?
Replies
15
Views
1K
Darter6
Darter6
R
What is this device?
Replies
5
Views
1K
oldbee
oldbee
Auto Transport Service
Back
Top