Possible side effect with Petronix ignition

[bighealeysource]

Hey all,
Installed a Petronix module a few weeks ago and my BN6 is running great and all is well. However, think I have a
minor weird after effect with the Petronix. When you turn the engine off, it will continue to run for a couple of
seconds and then turn off. Thought it might be a bad ignition swiitch so put in a new one and same thing happens when I turn it off. Doesn't diesel, just runs for one or two seconds and then shuts off. Buddy of mine thinks it could be due to the ignition module still having enough juice in it that it powers the coil and plugs for those additional one or two seconds. Anyone else have this with their Petronix module?
Thanks,
Mike

 

[whitworth]

I've experienced some post running with 'hot' ignitions. Easy fix, put in top gear, let clutch out fast as you're turning the key off. Works for me.

 

[SledLover]

I had Jeff at Advanced Distributors go through my '67 BJ8 distributor and install the Petronix module about 2 years ago, and have had no trouble whatsoever with it. When I shut off the ignition the engine immediately shuts down. I don't know how much power these draw, but is it possible there is a capacitor in your battery circuit that gets charged up and takes just a moment to discharge? Just a thought.

 

[Deleted member 8987]

Do you have electric fans?

 

[bighealeysource]

I do have an electric pusher fan installed on a separate, fused circuit.
Will switch it off and see if that makes a difference !
Thanks,
Mike

 

[Randy Forbes]

If the fan has a relay, as does my Moss sourced one, pull the relay out of its base.

 

[Deleted member 8987]

If you have a "slow" relay, it can hang in place enough to do that, until the relay releases or the fan slows enough.
Basically, the fan becomes a generator.

Why I asked......seen it.
Dave

 

[bighealeysource]

I don't have a relay on the fan. I do have it fused and has a toggle switch
mounted in the engine compartment so I can turn off for whatever reason.
Do I need a relay to protect anything ?
Thanks,
Mike

 

[Randy Forbes]

The relay just makes life on the switch contacts easier; "big" power running to the fan motor via the relay, and much lower current through the switch to control the relay (and hence, the fan).

Since I'm using a thermostatically controlled switch, the relay is a wise choice.

In your case, the test can be carried out by opening the switch, or pulling the fuse.

 

[Keoke]

Installed a Petronix module a few weeks ago and my BN6 is running great and all is well.

However, think I have a
minor weird after effect with the Petronix. When you turn the engine off, it will continue to run for a couple of
seconds and then turn off

Seems like plain ole run on to me most healeys will do it if overheated or the idle speed is too high. However, as for this being a unique problem to the pertronix unit in my opinion it is not.


Whitworth experienced some post running with 'hot' ignitions. His: Easy fix, put in top gear, let clutch out fast--- ----Do it slow as you're turning the key off then you will be OK. .__Fwiw--Keoke

 

[Cottontop]

Buddy of mine thinks it could be due to the ignition module still having enough juice in it that it powers the coil and plugs for those additional one or two seconds.

Your buddy is incorrect. The Pertronix I & II ingition modules are SIMPLY an electronic switch replacement for mechanical points.

A ring of rotating magnets open and close a Hall Effect (magnetic) transistor. The module's components do NOT have the capabilities to store, then dissipate, any current.

The Pertronix modules are also NOT an electronic ignition. They are simply magnetically controlled points.

The best bet to run-on is the electric fan until you rule it out.

Tonight, I drew a schematic for a fan control circuit for a Classic Mustang guy. It provides an optional always ON, Always OFF, and thermostatically controlled circuits.

This circuit will prevent your key contacts from becoming overloaded and will prevent any possibility of run-on.

Tim

 

[RAC68]

Hi All,

In another direction, as I remember, this is a condition that can happen with an alternator feedback. When the engine is shut down, the alternator does not immediately stop generating a current that can finds its way to the distributor. To eliminate this feedback current, I believe you install a diode on the ignition actuation line (the one with the ignition light). Others probably know more than I and can provide more accurate info.

All the best,
Ray (64BJ8P1)

 

[Keoke]

Yes Ray, what you are talking about makes some sense.Certainly if you put a forward biased diode in the main distributor power line, then that same diode will become back biased and prevent the alternator feedback which is of the reversed polarity from energizing the ignition circuit.--Keoke

 

[Keoke]

This circuit will prevent your key contacts from becoming overloaded and will prevent any possibility of run-on.

Don't think so as run on can be initiated by carbonised hot spots in the combustion chamber which are totally independant of the Key contacts.---Keoke

 

[Deleted member 8987]

Unfortunately, the description of "When you turn the engine off, it will continue to run for a couple of seconds and then turn off" seems to have generated many avenues of discussion.

I am guessing that bighealeysource (Mike) knows what run-on caused by pre-ignition due to hot spots, or vaccum leaks, or idle too high, or whatever.
Quote: "Doesn't diesel, just runs for one or two seconds and then shuts off."

Possibly feedback via the ignition lamp.....except the lamp would be lit when this problem occurs.......is it?
The electronic ignition probably works on less power than points, so feasable.

If the ignition switch works (and he replaced it already....no change), then the problem has to be in the ignition circuit.
There is no alternator or generator input into the ignition circuit once the switch is off.

Originally, anyway.

So, what do we have in the ignition circuit that could generate power we didn't have before?

Collapsing field on the fan as it slows, maybe?
Since he has a switch under the bonnet for the fan to "kill" it, simple test.
Turn the fan off, drive it.

Does this happen only when warm?

A more difficult test for one person is a test light or voltmeter on the power side of the coil (from ignition switch), set up running after a warmup jaunt, and turn the key off.
Does the test light stay lit for a while, then goes away and then the car shuts off?
Does the light get dimmer over those two seconds?

Now try it with the fan switch off.
Same thing?
Look at the ignition lamp.
If solved, it was fan.

We fought that fan-induced run-on for YEARS in shops, with add-on fans and even factory fans, from time to time.

Important troubleshooting clues.

 

[Cottontop]

Don't think so as run on can be initiated by carbonised hot spots in the combustion chamber which are totally independant of the Key contacts.

Correctamundo...

I should have said "This circuit will prevent your key contacts from becoming overloaded and will prevent any possibility of run-on <span style="font-weight: bold">by the fan inducing current into the ignition system</span>."

Tim

 

[Keoke]

If the ignition switch works (and he replaced it already....no change), then the problem has to be in the ignition circuit.
There is no alternator or generator input into the ignition circuit once the switch is off.

Well Maybe.However, there is still the potential for mutual or induced coupling between the inactive ignition wire circuit and an adjacent active circuit carrying the feed back signal in the wire harness. Similarly, the capacitance of the open switch can be a coupling mode also. OTOH, I never had a problem with Run-On / Dieseling that caused me to look this deep into the circuit to correct it.---Keoke

 

[Deleted member 8987]

DC coupling?
Yeah, maybe a tad as the field collapses, but certainly not enough to do THAT.
And, the main feed wires from the alternator (or generator) go to the starter solenoid (switch), no where near the ignition leads, of which they would have to be loomed together, tightly, parallel for how many feet to induce said voltage?

How for from here to Hoover Dam?

I'd have to dig out my old theory books from 1967 to see what levels could be generated.
AC, yes, but we'd best not have any AC component in our LBC's.

Dave

 

[Keoke]

Yes Tim, I thought that might be what you Had intended to say: :thumbsup:


-----------------------Keoke

 

[Keoke]

DC Coupling?

OH No of course not. It would be in the form of an AC transient and may be complicated even more if the unpowered open circuit line just happened to also be resonant at the transient frequency. However as I Said never had a problem with run on that required me to look that deep into the circuitry