Weak to no Spark, all of a sudden*****UPDATE****

1968 Dart.
Weak to no spark . Car started up this morning barely idled but kept cutting out.
Pulled the plugs and they were wet. Replaced the plugs and car still wont fire up.
Pulled a plug and watched for spark with ignition on the on position and its barely there and then none.
It has a stock distributor converted to Pertronix electronic no points.
Where do I go from here?

What's the voltage at the coil + terminal?

With the key in the on position. Positive red lead from volt meter black wire to battery ground, I get 5.3 volts

When out to the 51 and took some measurements.

It's a 51 Plymouth Cambridge I converted to 12v negative ground using a Mopar alternator and voltage regulator. Stock points ignition with Mopar ballast and 12v coil.

engine off, key in run I see 12.2V at the battery (low, should be 12.8v ish) and 6.2v at the coil +, all grounds taken at the battery negative terminal.

engine running, 12.8V at the battery (low, should be 13.8v ish, need to up the idle speed) and 8.8v at the coil +, all grounds taken at the battery negative terminal.

Pertronix says 8.0v minimum. You barely have the minimum for a 6v system. You aren't still running the ballast?

A LINK to the Pertronix test pdf.

For some reason your voltage at the coil is way low.

Not really sure how to proceed at this point. Ballast resistor is there as is the voltage regulator. its a stock distributor with Pertronix conversion to electronic ignition.
Car did start up initially but was running horribly. Plugs were fouled. Changed plugs out and it doesn't even want to run. Like I said, virtually a faint to no spark.

With the key on, engine off what's the voltage on both sides of the ballast?

One side had better be real close to battery voltage. that side comes from the ignition switch.

Pertronix failures are common.

Did you use their coil also?

If so, swap the old one back in & try it.

Going to check and see what it is.

What voltage on both sides??

Only did the conversion with the distributor.
Everything else is concours correct with dated coded parts.

Jump 12V to the Pertronix & if no go then its the P conversion in the dist that's at fault

The ballast resistor has two feeds from the ignition switch, one from the run position and one from the start position for feeding the coil + side 12.+ V when the starter is engaged. Once you turn the ignition switch in the run position you should see 12.+ volts on one side of the ballast resistor and around 6.0 to 8.0 volts on the other side going to the + side of the coil.
You should also see 12.+ V on the + side of the coil when you have the ignition switch in the start position also
If you have both of those voltage I would think the Pertronix module is the problem
Do you have a trouble shooting procedure for the Pertronix unit?

Only getting 5.5 at the positive side of the could in the on position. Is there a way to bypass the ballast resistor temporarily to see if the car starts?
If I dont have 12 volts at the ballast resistor, what is the fix for this?

Take a lead from the positive side of the battery and go to which wire on the distributor?

the one going to the coil positive primary terminal

just tell us what you got then we can go from there.

This is normal, now get someone to hold the ignition switch in the start position after you are ready to read the voltage going to the + side of the coil when the starter is wroking
let us know that voltage
Did you check the voltage on both sides of the ballast resistor with the ignition switch on? If not do that, one side should read around 12.+volts and the other side should read less than 8.0 Volts if you check it before it warms up and creates more resistance which will read less voltage like you have seen.

Pertronix requires a MINIMUM of 8.0v.

5.5 is not going to cut it and is why he's having issues.

I thought you were supposed to bypass the resistor with Pertronix.

I really depends on which Pertronix he is running.

The Ignitor use the ballast

The Ignitor II or III no ballast

Ballast resistor has 11.8 on the single wire blue and 5.5 on the double wire.
coil + has 5.5 at it.

11.8 is low, really low. What is the voltage at the battery terminals. Should be 12.6 or better.

You could try running a jumper from the batter + to the side of the ballast that reads 11.8 right now and try to start it. If it runs remember that you won't be able to shut it off till you pull the jumper. and it will narrow theisue down to before the ballast.

just checked and I have 13.6 at the battery.

Put the jumper wire on the ballast resistor side where there was 11.8 from the positive side of the battery. Nothing.
Pulled a plug and I get one spark then nothing. And its a weak spark.


Curious still 5.5 at the + side of the coil when in the on position. Why would this be? What would the distributor have to do with this?

Ok, so you are losing almost 2 volts between the battery and the ballast. Might be the ignition switch, or the bulkhead connections. Can you measure the voltage at the battery side of the ignition switch connector?

If it's close to 13.6, put the switch in run and measure the output of the switch.
If the input to the switch is close to 11.8 instead it's time to clean you bulkhead connector.

The ballast resistor is dropping the voltage to the coil like it was designed to do
The Petronix unit may be dropping it more than stock also

I'm going to call Pertronix tomorrow and see what they say.
Could the coil be bad? Or the voltage regulator?
Seems that the voltage regulator was an issue years ago on my cruiser.
That's why I was always carrying an extra voltage regulator.

So an update*****
Bought a new attery and have 12.0 at the single blue wire to ballast resistor.
Double wire from Ballast resistor has 12.0.
Tested Coil at Positive 5.5.
Pulled all wires off of coil and tested blue wire and it has 12.0 volts. Put back blue wire and radio suppressor to coil and still have 12.0 volts.
Put back the red PerTronix wire back on the positive terminal of coil and everything goes back to 5.5 and a very very weak spark and then nothing.
So I isolated the problem to the PerTronix system.

Well, after replacing the PERTRONIX IGNITOR with a NEW one.
Full spark and it starts right up.
Sending old one back..
It has only 125 miles on the setup.

Thank you for updating the forum. That is very considerate.
Jeff

Install a used, original 50 year old coil & send the 'new' Petronix one back also while you are at it to save on shipping.

My OE coil is fine.
It was just the Pertronix ignitor inside the distributor that went bad.
Rotor was also ok. Knew something was wrong when I watched the spark on a sparkplug go from 1 weak one to no spark at all. Have 12.0 volts from the blue wire to the positive side of the coil.
Weird but when you hook up the ignitor positive wire to it, it goes to 5.6 volts.
Even the new one but have a good spark now.
Dont know why it went bad. Only 125 miles on it.

That's because without the ignitor hooked up you have an open circuit and you will read battery voltage at the coil +. That's the nature of an open circuit.

Kinda late to the party... glad you solved your issue though


I read thru the thread, and I'll just mention that I've been using Pertronix conversions on my personal/customers vehicles/equipment/marine applications as well for about 30 years now without a single failure/issue to date....

I've found thru the years that most failures that others experience are from mismatched components, or improper installation, or not knowing some of the peculiarities of the various Pertronix systems...

You should eliminate the ballast resistor (I understand your need for an OEM look) to have a true 12 volts to the HallCell, just gut out the stock ballast resistor, and solder in an insulated piece of copper #10 or #12 wire between the 2 terminals, connect the harness terminals on the resistor as you normally would, the system will run so much better, and you will have eliminated a weak link in the system as well... for no resistor in the system connect the black Pertronix lead to the NEGATIVE terminal on the coil, and the RED Pertronix lead to the POSITIVE terminal on the coil, your BLUE/DARK BLUE ignition lead from the vehicles bulkhead will go on the POSITIVE terminal of the coil

Your running the Pertronix I, it has no internal safeguard to protect the HallCell if the key is left in the "run" position for more than 30 seconds without the engine running, if you must troubleshoot the electrical system in the future with the key in the "run" position for long periods of time, disconnect the RED Pertronix lead from the coil...

I'd recommend using the Pertronix Flame Thrower coil/epoxy filled, but if you insist on the OEM coil, make sure it's rated for 1.5 ohms for the Pertronix I on a V8 application

Run a copper terminal cap, avoid an aluminum terminal cap, no solid core plug wires ...

Just some tips to help you avoid any issues with your new Pertronix install




Mike

Thanks for taking the time to explain everything to me like that.
Just not sure why it happened in the 1st place. It's a show car and driven very little.
Pertronix was going to give me a warranty but I couldnt find the original receipt
As soon as I hooked up both wires and installed it in the distributor, it started right up with a nice strong spark.

You had to see my face when I hooked up the new ignitor and saw 5.5 volts again. But when I cranked over the engine with an exposed spark plug and saw a strong spark, I knew it was going to fire right up.

You did good troubleshooting it, next time you'll be more confident in you abilities.

Couldnt have done it without you. Thanks

Do be aware that the petronix units do not like to have power to them without the engine running. It will overheat the module and cause it to fail.
I'm not 100% sure if that applies ti the Ignitior 2 and 3 modules but it definitely does on the regular Ignitor.