Spark when key is turned to the off position?

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_Sam

_Sam

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I have a 73 dart with a 318 and edelbrock carb. I went out a couple days ago and started and it run for about 5 minutes. Today I decided to wash it but when I went to start it it wasn't having it. Immediately went to check for spark and noticed that nothing was happening while cracking but it would let off a little spark whenever I disengaged the key and moved it to the off position. Anyone have any idea whats going on?
 
Spark at the plugs? Check for power at the coil side of the ballast when cranking, or check continuity through the ballast.
 
If it starts for a moment when you let off the key, it sounds like a bad ballast resistor.
 
The one spark at key-off is normal, and proves the ECU and coil are working.

Look for moisture in the cap, and dry it out, also the top of the coil,needs to be dry
If you didn't get the engine wet, then swap in a new ballast resistor, as already said.
 
Try to start it and hold the key in the start position. If it starts while in the start position but quits when you release it to the run position, put a ballast resistor on it.

And no, it will not hurt a thing to hold the starter engaged for a few seconds just for diagnostic purposes.
 
RustyRatRod said:
Try to start it and hold the key in the start position. If it starts while in the start position but quits when you release it to the run position, put a ballast resistor on it.

And no, it will not hurt a thing to hold the starter engaged for a few seconds just for diagnostic purposes.
Click to expand...
What if u don`t run a ballast resistor, and it does it ??
 
I had an issue recently and it was a bad ground on the ignition module. I ran a ground wire to the mounting screw from the firewall.
 
The best test to get to the root of your problem is to use a voltmeter to view coil (-) to ground voltage as you crank the engine. The voltage should bounce, if it is always low, the ignition module is not triggering. The 2-pin connector that goes to pickup are often problematic, since car was recently washed, check there first. Clean, slightly squeeze female portions to tighten. Also check reluctor gap it should be about 0.008" using brass or plastic feeler. Also check pickup coil resistance it should be 290-350 Ohms.
 
Sounds like no signal from the distributor to me.
Check and slightly crimp the distributor pigtail would be the very first thing I would try.
(If my car had one)
I removed that connector just because of that.
Then you can go on to harder stuff.
 
KitCarlson said:
The best test to get to the root of your problem is to use a voltmeter to view coil (-) to ground voltage as you crank the engine. The voltage should bounce, if it is always low, the ignition module is not triggering. The 2-pin connector that goes to pickup are often problematic, since car was recently washed, check there first. Clean, slightly squeeze female portions to tighten. Also check reluctor gap it should be about 0.008" using brass or plastic feeler. Also check pickup coil resistance it should be 290-350 Ohms.
Click to expand...

THIS RIGHT HERE

Also disconnect the distributor, take the engine bay end of the connector and with the key in run tap the exposed terminal of the two terminal connector to ground. It should make one "snap" spark AT THE COIL WIRE each time.

Pull the cap, inspect for moisture, dirt, etc, and inspect the rotor for "punch through" or other damage. Inspect the reluctor/ pickup for strike damage, debri stuck to the magnet, and other damage. "Wiggle" the shaft and check for play
 
TrailBeast said:
Sounds like no signal from the distributor to me.
Check and slightly crimp the distributor pigtail would be the very first thing I would try.
(If my car had one)
I removed that connector just because of that.
Then you can go on to harder stuff.
Click to expand...

We'uns both typing..................LOL
 
famous bob said:
What if u don`t run a ballast resistor, and it does it ??
Click to expand...
All Chrysler ECUs that I have tested do the one spark thing,at voltage collapse to the coil . I imagine all standard coils do that if the negative side is rapidly interrupted. I mean It's just like the points are being opened right? The ECU is just an amp for the pick-up, and a current breaking system; a glorified, maintenance free, set of points, that don't suffer from premature point-bounce.
 
AJ/FormS said:
All Chrysler ECUs that I have tested do the one spark thing,at voltage collapse to the coil . I imagine all standard coils do that if the negative side is rapidly interrupted. I mean It's just like the points are being opened right? The ECU is just an amp for the pick-up, and a current breaking system; a glorified, maintenance free, set of points, that don't suffer from premature point-bounce.
Click to expand...
Describing the ECU as an amp is not exact. Yes it has a transistor that pulls the coil (-) to ground, but the interface to the reluctor sensor does not resemble an amplifier. The interface rejects the negative swing of signal, then triggers at a point a few tenths of a volt above the zero cross transition. The pickup signal amplitude increases proportionally with engine RPM. The cranking signal with too much reluctor to pickup gap, signal ampitude is too low, and may will result in no start. It may have been running well at idie before shutoff, the signal at idle 3 to 4 times greater than cranking signal.
The amplitude threashold after zero cross, mentioned earlier is necessary for noise immunity, without the ignition would falsely trigger between reluctor teeth, and by EMI.
The spark _Sam gets when key is turned off, happens because the ignition switch interrupts the coil current, however the rotor is pointing to a random place, so spark may not make it to a plug.
 
Just to clarify the car never got washed so it should be dry so that should not be an issue. And the car will not start at all. The car started the other day and ran fine. Now the car won't start at all. So that should not be a ballast resistor problem right?
 
also does the ballast resistor need to be mounted to the car as far as a ground? the resistor just kind of sits there and is not mounted but as far as I can remember its been like that. Could that be an issue?
 
_Sam said:
also does the ballast resistor need to be mounted to the car as far as a ground? the resistor just kind of sits there and is not mounted but as far as I can remember its been like that. Could that be an issue?
Click to expand...
It isn't grounded, but if it's just hanging by the wires, that can cause some issues.

If you have a ballast resistor with 4 connections, this sounds like the .5 ohm side of the ballast is burnt out (or broken) . This is a pretty typical failure for the symptoms you describe in your first post. Since your car is a '73, I would expect to see that type of ballast resistor.

What happens is when you turn the key to "start", the current runs through the .5 ohm side of the ballast. When you release the key and it goes to "run", you are using the 5 ohm side of the resistor.

So... If your ballast is just hanging by the wires, there's a good chance the resistor on the "start" side broke.

If you have a ballast resistor with only 2 connections, pay no attention to what I just typed.
 
Ballast resistor with 4 connections

FDF.jpg


2 connections

GQWV1sf9.iNfBJXf14.JvV%25GQ9V1N5g1sf9%25GQg1N5WBQvoNf9WCf%25GQprS%25GQz8G.%3Dgs%26gPIfm-Y%2CHbEH.jpg
 
Big_John said:
It isn't grounded, but if it's just hanging by the wires, that can cause some issues.

If you have a ballast resistor with 4 connections, this sounds like the .5 ohm side of the ballast is burnt out (or broken) . This is a pretty typical failure for the symptoms you describe in your first post. Since your car is a '73, I would expect to see that type of ballast resistor.

What happens is when you turn the key to "start", the current runs through the .5 ohm side of the ballast. When you release the key and it goes to "run", you are using the 5 ohm side of the resistor.

So... If your ballast is just hanging by the wires, there's a good chance the resistor on the "start" side broke.

If you have a ballast resistor with only 2 connections, pay no attention to what I just typed.
Click to expand...

Sorry this is not true. At least not as you explained it. One side of the resistor supplies the COIL and the other side supplies the ECU. THAT is the half that was deleted. The coil side has never changed so far as the circuit. IN FACT if the ECU goes bad, you can pull the ECU connector, drop in an old points distributor, hook the dist. to the coil NEG and if the ECU was the only problem, it will run

When you START the car with a 4 terminal ballast, "things are a trick." There is no "ignition run" power during start, the coil PLUS is powered through the ballast bypass (brown, IGN2) circuit. So the power BACKFEEDS through the resistor to power the ECU during crank. VERY POOR DESIGN in my opinion

Here is the circuit. The "ignition run" at lower right is DEAD during cranking. Only power to the circuit comes from "Ignition 2" pink in the diagram

Current flow from coil is from ECU ground, through box switching transistor, to coil NEG and through coil, out coil + and back to battery through the pink "ign 2"

Box circuit is from ECU ground, out pin 1, through resistor from right to left lower section, out resistor and back to battery on pink

Other section is s from ECU ground, out pin 3 (blue) to top section of resistor, through top section from left to right, through bottom section from right to left, and back to battery on pink.

This is "properly described" as neg to pos electron flow

MoparIgnition.jpg
 
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MORE: The vast majority of ECU boxes you run into are ACTUALLY more modern 4 pin boxes, which only require a TWO pin resistor, but "can" run with a 4 pin installed. The "other half" is simply not used

This simplified circuit omits the "ign2" bypass and shows the "run" as "existing wire" off to top right. THIS CIRCUIT shows that the coil resistor is same as points.........feeds from points (transistor switch) up through coil, up through resistor, and back to the battery. "Just like" the 4 pin, in start, the resistor has to feed the box to power it during cranking. The "existing" wire is dead. ONLY POWER is IGN2 "bypass" being fed to coil+ during "start"
 
Here is how the 2 pin resistor start circuit works:

From ground, through the ECU box, through the switch, through the coil, out coil + to the bypass "start" wire

From ground through the ECU, out pin "blue" up through the resistor, and back to battery on "start" wire. This is a misnomer, it is IGN2, not the "start" wire

Moparimage002.jpg
 
67Dart273 said:
Sorry this is not true. At least not as you explained it. One side of the resistor supplies the COIL and the other side supplies the ECU. THAT is the half that was deleted. The coil side has never changed so far as the circuit. IN FACT if the ECU goes bad, you can pull the ECU connector, drop in an old points distributor, hook the dist. to the coil NEG and if the ECU was the only problem, it will run

When you START the car with a 4 terminal ballast, "things are a trick." There is no "ignition run" power during start, the coil PLUS is powered through the ballast bypass (brown, IGN2) circuit. So the power BACKFEEDS through the resistor to power the ECU during crank. VERY POOR DESIGN in my opinion

Here is the circuit. The "ignition run" at lower right is DEAD during cranking. Only power to the circuit comes from "Ignition 2" pink in the diagram

Current flow from coil is from ECU ground, through box switching transistor, to coil NEG and through coil, out coil + and back to battery through the pink "ign 2"

Box circuit is from ECU ground, out pin 1, through resistor from right to left lower section, out resistor and back to battery on pink

Other section is s from ECU ground, out pin 3 (blue) to top section of resistor, through top section from left to right, through bottom section from right to left, and back to battery on pink.

This is "properly described" as neg to pos electron flow

View attachment 1715152060
Click to expand...

Thanks for the detailed explanation. I stand corrected and have just learned something. I'll have to read more on this.

67Dart273 said:
MORE: The vast majority of ECU boxes you run into are ACTUALLY more modern 4 pin boxes, which only require a TWO pin resistor, but "can" run with a 4 pin installed. The "other half" is simply not used

This simplified circuit omits the "ign2" bypass and shows the "run" as "existing wire" off to top right. THIS CIRCUIT shows that the coil resistor is same as points.........feeds from points (transistor switch) up through coil, up through resistor, and back to the battery. "Just like" the 4 pin, in start, the resistor has to feed the box to power it during cranking. The "existing" wire is dead. ONLY POWER is IGN2 "bypass" being fed to coil+ during "start"
Click to expand...

While it's true that most ECU boxes have probably been replaced with the more modern 4 pin unit, we don't know that is true with the OP's car.

The '73 cars originally had a 5 pin ECU with a dual ballast resistor. I think we can agree on that... and agree that we don't know what ECU is in that car right now. If it is a 5 pin ECU, I think we could also agree that if the side of the ballast resistor used in the "start" circuit is bad, the car won't start.

Regardless of my incorrect explanation, I think that given the description by the OP of "no spark" while starting and "spark" as the key is released, it kinda points to an issue with the "start" circuit. (at least that's the way I read the first post)

So... While that could be a lot of issues, given that the car is a '73 with quite possibly a 5 pin ECU, the backyard mechanic in me will point at the ballast resistor as being the easiest and quickest thing to check. With the little tidbit about the ballast not being bolted down, I would be even more suspicious that there was physical damage to the ceramic and that has caused the ballast resistor to fail.

We can debate it ad nauseum, but bottom line it that it's a simple check to replace the ballast resistor with the spare that most Mopar guys carry in their glovebox as a sacrifice to the gods of spark. Given that the OP hasn't gotten out his DMM and diagnosed the ignition circuits before posting and we're giving advice over the internet.. well... if it runs, great... If not... it's something else.
 
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