Ignition question involving use of ballast resistor

1987 Dodge Dakota 3.9L carbed

I recently posted on rec.autos.tech about the problems I was having with
an MSD 5900 Blaster ignition and an MSD 8202 Baster 2 coil. It seems I
could use one or the other with no problem, either the MSD ignition with
the stock coil or the MSD coil with the stock ignition, but if I had
both installed I would get a stumble on accelerating from a dead stop.

From this behavior I deduced that, for some reason, the problem was
being caused by too much ignition voltage. To test out that theory I
installed a 1 ohm ballast resistor in line with the +12 volts going to
the coil. Voila, the problem vanished and I was back to strong, smooth
acceleration from a dead stop. So then I tried a 1/2 ohm ballast
resistor and the stumble returned, but not as bad, so I went back to the
1 ohm resistor.

The stock coil has about a 1.5 ohm primary and the MSD coil has a .7 ohm
or so primary. I don't know what impact this has on the situation but
it's info that I have and I figured I might as well throw it in if I am
going to all the trouble of posting this and you are going to all the
trouble of reading it.

Now we get to meat of the my puzzlement. The ignition wires that I have
on the engine measure about 3000 ohms per foot. For about $45 I can buy
some MSD Street Fire wires that are only 500 ohms per foot. I know a bit
about electricity, but not enough to know whether or not these wires
would enable me to run the MSD ignition and coil without the ballast
resistor. After all, the point of an MSD ignition upgrade is to get
longer stronger spark to the plug.

I don't have a clue as to why the engine stumbles with both the MSD
ignition and coil installed. From the symptoms it seems to me that it
must be because of too much voltage at the coil tower, but why that
might be causing the problem is beyond me.

Could it be because the high voltage is leaking out to ground somewhere
on the way to the plugs? I checked the engine at idle in a dark area at
night and saw no evidence of arcing. Could the high resistance wires be
the cause? If so, what is the rationale? I can't think of one.

Well that's it. At present, I am more than happy with the ballast
resistors. The truck runs great. Just curious as hell as to what might
be going on.

Jack

ROTFLMAO !!!

Jack,
The purpose of a ballast resister is to allow a lower voltage ignition coil
to be used. The reason for this is that when the starter motor is engaged,
battery voltage will drop to say 8 V. You will note that when wired
correctly the ballast resister is bypassed at that time allowing the coil to
create adequate spark during lower battery voltage conditions . When the
starter is then disengaged the resister bypass is also dropped and the
resister is now in play to reduce excessive heating of the coil. Electronic
ignitions are very sensitive to coil configurations, as they provide coil
drive and can be permanently damaged if the DC resistance of the coil is too
low. Follow the manufacturer's recommendations.
Steve

"Jack" > wrote in message
...
> 1987 Dodge Dakota 3.9L carbed
>
> I recently posted on rec.autos.tech about the problems I was having with
> an MSD 5900 Blaster ignition and an MSD 8202 Baster 2 coil. It seems I
> could use one or the other with no problem, either the MSD ignition with
> the stock coil or the MSD coil with the stock ignition, but if I had
> both installed I would get a stumble on accelerating from a dead stop.
>
> From this behavior I deduced that, for some reason, the problem was
> being caused by too much ignition voltage. To test out that theory I
> installed a 1 ohm ballast resistor in line with the +12 volts going to
> the coil. Voila, the problem vanished and I was back to strong, smooth
> acceleration from a dead stop. So then I tried a 1/2 ohm ballast
> resistor and the stumble returned, but not as bad, so I went back to the
> 1 ohm resistor.
>
> The stock coil has about a 1.5 ohm primary and the MSD coil has a .7 ohm
> or so primary. I don't know what impact this has on the situation but
> it's info that I have and I figured I might as well throw it in if I am
> going to all the trouble of posting this and you are going to all the
> trouble of reading it.
>
> Now we get to meat of the my puzzlement. The ignition wires that I have
> on the engine measure about 3000 ohms per foot. For about $45 I can buy
> some MSD Street Fire wires that are only 500 ohms per foot. I know a bit
> about electricity, but not enough to know whether or not these wires
> would enable me to run the MSD ignition and coil without the ballast
> resistor. After all, the point of an MSD ignition upgrade is to get
> longer stronger spark to the plug.
>
> I don't have a clue as to why the engine stumbles with both the MSD
> ignition and coil installed. From the symptoms it seems to me that it
> must be because of too much voltage at the coil tower, but why that
> might be causing the problem is beyond me.
>
> Could it be because the high voltage is leaking out to ground somewhere
> on the way to the plugs? I checked the engine at idle in a dark area at
> night and saw no evidence of arcing. Could the high resistance wires be
> the cause? If so, what is the rationale? I can't think of one.
>
> Well that's it. At present, I am more than happy with the ballast
> resistors. The truck runs great. Just curious as hell as to what might
> be going on.
>
> Jack

Jack wrote:
>
> 1987 Dodge Dakota 3.9L carbed
>
> I recently posted on rec.autos.tech about the problems I was having with
> an MSD 5900 Blaster ignition and an MSD 8202 Baster 2 coil. It seems I
> could use one or the other with no problem, either the MSD ignition with
> the stock coil or the MSD coil with the stock ignition, but if I had
> both installed I would get a stumble on accelerating from a dead stop.
>
> From this behavior I deduced that, for some reason, the problem was
> being caused by too much ignition voltage. To test out that theory I
> installed a 1 ohm ballast resistor in line with the +12 volts going to
> the coil. Voila, the problem vanished and I was back to strong, smooth
> acceleration from a dead stop. So then I tried a 1/2 ohm ballast
> resistor and the stumble returned, but not as bad, so I went back to the
> 1 ohm resistor.

Normally when all is working as it should, what limits voltage is the spark
plug gap and the engine compression (actually the absolute pressure inside
the cylinder). A wider gap or more pressure will cause the voltage to climb
higher before it will cross the gap. acceleration from a stop often will
produce the greatest pressure inside the cylinder.



>
> Could it be because the high voltage is leaking out to ground somewhere
> on the way to the plugs?

Yes it could be that - If the voltage climbs too high too fast it finds
another path instead of the spark plug gap. Ultimately, your ballast
resister doesn't limit the voltage at the spark plug but it does slow down
the rise in voltage which means that some other points in the secondary
won't get quite as high. If stray arcing in the secondary is what is
happening it would be likely that it would get progressively worse over time
as the stray arcs develops a carbon trail that the current can follow more
easily.

The cause could also be in the primary there may be something that
saturates in the primary or even something intended to limit voltage/current
to protect against damage.

-jim





>I checked the engine at idle in a dark area at
> night and saw no evidence of arcing. Could the high resistance wires be
> the cause? If so, what is the rationale? I can't think of one.
>
> Well that's it. At present, I am more than happy with the ballast
> resistors. The truck runs great. Just curious as hell as to what might
> be going on.
>
> Jack

> Normally when all is working as it should, what limits voltage is the
> spark
> plug gap and the engine compression (actually the absolute pressure inside
> the cylinder). A wider gap or more pressure will cause the voltage to
> climb
> higher before it will cross the gap. acceleration from a stop often will
> produce the greatest pressure inside the cylinder.

This was especially true when the Kettering system was used. When
capacitive
discharged systems came along, it pretty much stopped being true. Their
rise times are so short and transformer action so definite that they usually
put
up much more constant ignition performance.

I dont know what the multiple spark discharge systems do. Are they CD, or
something else?

Some early studies showed that, all things being equal, a small single spark
ignited the fuel as well as anything else. Some university studies in
England
showed that high performance ignition systems which gave significant gains
were possible, but they were not necessarily simple and cheap either.

It is my opinion, and nothing more, that there is little to be gained from
systems
like the MSD for normal driving. For racing, maybe....

Jack > wrote:
>From this behavior I deduced that, for some reason, the problem was
>being caused by too much ignition voltage. To test out that theory I
>installed a 1 ohm ballast resistor in line with the +12 volts going to
>the coil. Voila, the problem vanished and I was back to strong, smooth
>acceleration from a dead stop. So then I tried a 1/2 ohm ballast
>resistor and the stumble returned, but not as bad, so I went back to the
>1 ohm resistor.

The ballast resistor does more than just change the voltage, it can change
the shape of the pulse through the coil as well.

>Now we get to meat of the my puzzlement. The ignition wires that I have
>on the engine measure about 3000 ohms per foot. For about $45 I can buy
>some MSD Street Fire wires that are only 500 ohms per foot. I know a bit
>about electricity, but not enough to know whether or not these wires
>would enable me to run the MSD ignition and coil without the ballast
>resistor. After all, the point of an MSD ignition upgrade is to get
>longer stronger spark to the plug.

No, using a wire with a lower resistance will _slightly_ increase the
voltage to the plug. But honestly, the difference is very small because
the voltage is so high and current so low that it takes a lot of resistance
to cause much drop.

>I don't have a clue as to why the engine stumbles with both the MSD
>ignition and coil installed. From the symptoms it seems to me that it
>must be because of too much voltage at the coil tower, but why that
>might be causing the problem is beyond me.

What you want is an ignition system analyzer that will let you look at the
signal coming out of the coil on a CRT. This will tell you what is really
happening when you put the ballast resistor in. Ask older shops around town
if they still have an analyzer kicking around.

>Well that's it. At present, I am more than happy with the ballast
>resistors. The truck runs great. Just curious as hell as to what might
>be going on.

The scope will tell you, and without the scope you have no real chance of
seeing what is happening.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

HLS wrote:
>
> > Normally when all is working as it should, what limits voltage is the
> > spark
> > plug gap and the engine compression (actually the absolute pressure inside
> > the cylinder). A wider gap or more pressure will cause the voltage to
> > climb
> > higher before it will cross the gap. acceleration from a stop often will
> > produce the greatest pressure inside the cylinder.
>
> This was especially true when the Kettering system was used. When
> capacitive
> discharged systems came along, it pretty much stopped being true.


What stopped being true? The statement you are responding to has never stopped
being true. It may have become unimportant to know that it is true, but that is
hardly the same as being not true..


> Their
> rise times are so short and transformer action so definite that they usually
> put
> up much more constant ignition performance.

How does this information relate to solving the OP's problem? The rate at which
voltage is developed in the coil is going to be a function of resistance and
inductance no matter what. Which is why changing resistance produces different
results.

>
> I dont know what the multiple spark discharge systems do. Are they CD, or
> something else?
>
> Some early studies showed that, all things being equal, a small single spark
> ignited the fuel as well as anything else. Some university studies in
> England
> showed that high performance ignition systems which gave significant gains
> were possible, but they were not necessarily simple and cheap either.
>
> It is my opinion, and nothing more, that there is little to be gained from
> systems
> like the MSD for normal driving. For racing, maybe....

His intent is related to neither of those - it is to improve emissions.

-jim

Jack wrote:

> 1987 Dodge Dakota 3.9L carbed
>
> I recently posted on rec.autos.tech about the problems I was having with
> an MSD 5900 Blaster ignition and an MSD 8202 Baster 2 coil. It seems I
> could use one or the other with no problem, either the MSD ignition with
> the stock coil or the MSD coil with the stock ignition, but if I had
> both installed I would get a stumble on accelerating from a dead stop.
>
> From this behavior I deduced that, for some reason, the problem was
> being caused by too much ignition voltage. To test out that theory I
> installed a 1 ohm ballast resistor in line with the +12 volts going to
> the coil. Voila, the problem vanished and I was back to strong, smooth
> acceleration from a dead stop. So then I tried a 1/2 ohm ballast
> resistor and the stumble returned, but not as bad, so I went back to the
> 1 ohm resistor.
>
> The stock coil has about a 1.5 ohm primary and the MSD coil has a .7 ohm
> or so primary. I don't know what impact this has on the situation but
> it's info that I have and I figured I might as well throw it in if I am
> going to all the trouble of posting this and you are going to all the
> trouble of reading it.

I'm going to say MSD designed the output section of their ignition
system wrong, and maybe when the resistance is low, it goes into
current-limiting mode to protect itself. Another possibility is the
high voltage protection for the output section (typically some zener
diodes and capacitor) is interacting badly with the coil primary.

> Now we get to meat of the my puzzlement. The ignition wires that I have
> on the engine measure about 3000 ohms per foot. For about $45 I can buy
> some MSD Street Fire wires that are only 500 ohms per foot. I know a bit
> about electricity, but not enough to know whether or not these wires
> would enable me to run the MSD ignition and coil without the ballast
> resistor. After all, the point of an MSD ignition upgrade is to get
> longer stronger spark to the plug.

Low resistance actually doesn't help in most cases, probably because
it slows the rise time (turn-on) of the current, and I've heard of
many people running into trouble when they switched to low-resistance
plug wires.

High voltage leakage shouldn't be a problem with modern (1980s and
later) distributor caps, rotors, and wires. On the other hand after I
installed a CD ignition in my 1975 Dodge Dart, 2 caps cracked in a few
months. A slight modification to limit the primary voltage to under
400V stopped this.

HLS wrote:

> I dont know what the multiple spark discharge systems do. Are they CD, or
> something else?

They're usually ordinary flyback systems, just like points systems. I
never saw a CD multistrike system, but that was long ago, when every
CD system was triggered by an SCR, a device that can be turned on but
not turned off. But since then, high voltage, high current devices
that can be turned off have become more common, so multistrike CD
should be easier to implement. I had a double-strike CD system that
consisted of 2 separate CD units because I didn't know how to make
anything better.

> It is my opinion, and nothing more, that there is little to be gained from
> systems like the MSD for normal driving. For racing, maybe....

True, thanks to the EPA and its stringent emissions standards that
include cold weather, cold engine conditions.

I would suspect that too much primary current just supersaturates the
coil and it doesn't discharge properly, inhibiting the next charge/
discharge cycle.

Dan