Ignition question involving use of ballast resistor

HLS > wrote:
>"Scott Dorsey" > wrote in message
...
>
>> I am not really sure... I think you can look at the cable as a lumped-sum
>> anyway. It's pretty much just the resistance of the cable that will
>> affect
>> how much the coil will ring on the tail end of the pulse, and I think that
>> is the big deal.
>
>The inductance and the capacitance form the resonant circuit. The
>resistance
>is related to the Q, or quality factor.

Yes, but the thing is that the coil inductance and the distributed
inductance of the coil are so enormous that the cable doesn't contribute
a whole lot. The cable impedance is pretty heavily swamped.

Someone mentioned spiral-wound cables for RF suppression... I have never
used such a thing, but they could have enough series inductance to change
things. The most important part of that is that they will be a low
pass filter.

>The resonant circuit is responsible for the ringing.
>
>I believe, anyway>)

It is, but the coil resonance itself is so substantial that the cable
shouldn't change it TOO much.

It would be fun to measure it with a scope, though, and see how changing
the cable length alters the waveform. It bet it doesn't do much, but it
would be fun to see.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

jim wrote:
>
> Jack wrote:
>
>>>> 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.
>
> My guess is the cause is in the primary not the secondary. But if it was due
> to a leak in the secondary you would probably have to be looking at it in
> the dark while it was happening.
> Changing the spark plug wire resistance shouldn't have any effect. Current
> doesn't really flow thru the wires until the spark plug starts to arc. The
> tail end of the wave form will be affected but not the initial spike.
> Getting rid of the resistance won't change the peak voltage in a measurable
> way.
>
> It is not clear how this is going to help with your emissions. If the
> mixture ia a bit rich all the spark in the world is going to get the extra
> fuel to burn. If it is a tad lean it might help, but it doesn't sound like
> that is the case.
>
> -jim

I will find out soon what the emissions are. I just got back from a
freeway run and some stop and go driving and the only problem was a sag
when I floored it at about 25 to 35 mph, like the accelerator pump was
out of adjustment or the power valve was not opening. I tweaked the pump
linkage a bit but it wasn't out that much. I checked timing and it is at
spec. Checking the power valve will involve tearing into the carb, which
I will save for another day. It could be that the main jets are a tad
too small, but before I do anything else I will take it to a smog shop
for a dry run to see what the emissions are. At least the ignition
system seems to be performing okay and that was my main worry.

On Dec 30, 6:56*pm, 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

2 ppm HC is easy.
Retard the timing 2 degrees and it will drop right down...
Just to cover the bases...
Is the Cat OK? a temp gun should show a hotter outlet than inlet.
Does it run hot enough? No 160 TStat?
Absolutely no misfires? A dollar bill held up to the exhaust should
not vibrate.
HTH,
Ben

ben91932 wrote:
> On Dec 30, 6:56 pm, 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
>
> 2 ppm HC is easy.
> Retard the timing 2 degrees and it will drop right down...
> Just to cover the bases...
> Is the Cat OK? a temp gun should show a hotter outlet than inlet.
> Does it run hot enough? No 160 TStat?
> Absolutely no misfires? A dollar bill held up to the exhaust should
> not vibrate.
> HTH,
> Ben


Thanks, Ben, I'll definitely keep that in mind when the time comes.
5 BTDC shouldn't look that much different from 7 BTDC.

There has been an annoying misfire at idle for quite some time, although
with the current ignition system that I described elsewhere on the
thread, the idle seems to have smoothed out considerably. But the smog
test I have to take doesn't cover idle. It covers 15 and 25 mph on a
dynamometer. Sometime in the next week or two I am going to get a dry
run at the smog shop to see what it's reading.

Scott Dorsey wrote:
> 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

The modern equipment would be the Snap On Modis or the Snap On Vantage Pro.

On Jan 1, 12:33*am, Jack > wrote:
> ben91932 wrote:
> > On Dec 30, 6:56 pm, 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
>
> > 2 ppm HC is easy.
> > Retard the timing 2 degrees and it will drop right down...
> > Just to cover the bases...
> > Is the Cat OK? a temp gun should show a hotter outlet than inlet.
> > Does it run hot enough? No 160 TStat?
> > Absolutely no misfires? A dollar bill held up to the exhaust should
> > not vibrate.
> > HTH,
> > Ben
>
> Thanks, Ben, I'll definitely keep that in mind when the time comes.
> 5 BTDC shouldn't look that much different from 7 BTDC.
>
> There has been an annoying misfire at idle for quite some time, although
> with the current ignition system that I described elsewhere on the
> thread, the idle seems to have smoothed out considerably. But the smog
> test I have to take doesn't cover idle. It covers 15 and 25 mph on a
> dynamometer. Sometime in the next week or two I am going to get a dry
> run at the smog shop to see what it's reading.- Hide quoted text -
>
> - Show quoted text -

Jack,

from readin gall the above posts, my GUESS is that the combination
taht casues the stumble is for some reason casuing a WEAK spark. As
one poster said, it is hardest to develop spark during acceleration
when compression is the highest, so I guess there is some interaction
in the electronics and the coil such that you have a poor spark at
that time. Somehow the 1 Ohm ballast cures the interaction. I would
leave the 1 Ohm in the circuit and be happy, but if you want to
analyze this further I agree with another postr, you will need a scope
or ignition analyzer to look at the SECONDARY waveforms and see just
what is going on with and without the ballast.

also as far as I know, the purpose of resistance plug wires is to
reduce radio interference. They don't really lower or raise the
voltage of the spark AT THE PLUG.

You are doing a great job at narrowing in on this.. but I think you
need a scope to get to the next step.

Mark

wrote:
> On Jan 1, 12:33 am, Jack > wrote:
>> ben91932 wrote:
>>> On Dec 30, 6:56 pm, 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
>>> 2 ppm HC is easy.
>>> Retard the timing 2 degrees and it will drop right down...
>>> Just to cover the bases...
>>> Is the Cat OK? a temp gun should show a hotter outlet than inlet.
>>> Does it run hot enough? No 160 TStat?
>>> Absolutely no misfires? A dollar bill held up to the exhaust should
>>> not vibrate.
>>> HTH,
>>> Ben
>> Thanks, Ben, I'll definitely keep that in mind when the time comes.
>> 5 BTDC shouldn't look that much different from 7 BTDC.
>>
>> There has been an annoying misfire at idle for quite some time, although
>> with the current ignition system that I described elsewhere on the
>> thread, the idle seems to have smoothed out considerably. But the smog
>> test I have to take doesn't cover idle. It covers 15 and 25 mph on a
>> dynamometer. Sometime in the next week or two I am going to get a dry
>> run at the smog shop to see what it's reading.- Hide quoted text -
>>
>> - Show quoted text -
>
> Jack,
>
> from readin gall the above posts, my GUESS is that the combination
> taht casues the stumble is for some reason casuing a WEAK spark. As
> one poster said, it is hardest to develop spark during acceleration
> when compression is the highest, so I guess there is some interaction
> in the electronics and the coil such that you have a poor spark at
> that time. Somehow the 1 Ohm ballast cures the interaction. I would
> leave the 1 Ohm in the circuit and be happy, but if you want to
> analyze this further I agree with another postr, you will need a scope
> or ignition analyzer to look at the SECONDARY waveforms and see just
> what is going on with and without the ballast.
>
> also as far as I know, the purpose of resistance plug wires is to
> reduce radio interference. They don't really lower or raise the
> voltage of the spark AT THE PLUG.
>
> You are doing a great job at narrowing in on this.. but I think you
> need a scope to get to the next step.
>
> Mark
>

Thanks, Mark for the encouragement. I am *more* than happy with the
ballast resistor. After I got things working right by putting one in the
system, I googled "ballast" at the msdigntion.com/forum site:

http://www.google.com/search?sourcei...tion.com/forum

and came up with a whole slew of posts regarding using a ballast
resistor to compensate for the low primary resistance of the MSD coil
when used on a mechanical distributor ignition that uses a magnetic or
Hall effect pickup and electronics to fire the coil. The primary of the
MSD coil is .7 ohms and the replacement stock coil that I had been using
was 1.7 ohms measured with a digital meter.

MSD mentions nothing in their instruction sheet for the coil or ignition
about using a ballast resistor except when points are involved. Neither
is this info on any of the pages of their website except buried in the
forums in answer to questions of people who are trying to install their
units. So, according to the advice of the MSD techs, I did the correct
thing, but it sure would have been a helluva lot less time and nerve
consuming had they discussed the need for a ballast resistor in a
non-points distributor in their instructions.

In all the advice to people asking about this the techs would invariably
state that *NOT* using a ballast resistor could result in the failure of
the electronics that fires the coil in non-points systems. You would
think that a company like MSD would be more thorough in explaining in
their installation instructions the correct way to wire up their units
without causing damage to your vehicles electronics, but here we are.

I'm glad I held off buying low resistance wires. It didn't make sense to
me that they would correct the problem I was having.

>
> 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

Read Dans' reply more closely.

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

Your post centered aound the ballast resistor selections. And Dans
post says it all. Perhaps things would be improved by a RF coil or
choke with a resistance of the same ohmage as the ballast resistor you
have determined to work well.

The secondary voltage is not really effected by the plug and or wire
resistance. Perhaps by their construction. The signal at the plugs is
really a complex Radio Frequency waveform that without a good scope
can not be interpreted. The usual monitor scope found in the garage is
not up to this.

And finally the manufacturer of your ignition should probably not be
in businees at all. They know little if anything about ignition
systems. You vehicle manufacturer should be relied on. Contact their
high performance folks for advice and guidance. Undoubly the
manufacturer maximized the performance of your original ignition.

Bob AZ

Bob AZ wrote:
>> 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
>
> Read Dans' reply more closely.
>
> 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
>
> Your post centered aound the ballast resistor selections. And Dans
> post says it all. Perhaps things would be improved by a RF coil or
> choke with a resistance of the same ohmage as the ballast resistor you
> have determined to work well.
>
> The secondary voltage is not really effected by the plug and or wire
> resistance. Perhaps by their construction. The signal at the plugs is
> really a complex Radio Frequency waveform that without a good scope
> can not be interpreted. The usual monitor scope found in the garage is
> not up to this.
>
> And finally the manufacturer of your ignition should probably not be
> in businees at all. They know little if anything about ignition
> systems. You vehicle manufacturer should be relied on. Contact their
> high performance folks for advice and guidance.

The vehicle manufacturer, Chrysler, is the one that stuck me with an
electronic feedback carburetor for which I cannot buy a replacement
mixture control solenoid.

Do you really think they would grace me with advice and guidance?

Get real.

> Undoubly the
> manufacturer maximized the performance of your original ignition.
>
> Bob AZ
>
>

>
> The vehicle manufacturer, Chrysler, is the one that stuck me with an
> electronic feedback carburetor for which I cannot buy a replacement
> mixture control solenoid.
>
> Do you really think they would grace me with advice and guidance?
>
> Get real.
>
>
>
> > Undoubly the
> > manufacturer maximized the performance of your original ignition.
>
> > Bob �AZ-

Jack

All things considered I do believe the manufacturer is a good source.
I have contacted Chrysler myself and received good advice. And after a
long evening conversation with a Ford Ignition Systems Engineer I am
more aware of the choices that the manufactures make.

Remember I advised to contact the manufacturers Performance folks.
They have a periodic magazine that is available by subscription. I
read all the issues at the dealer while getting my car and truck
serviced.

Chrysler, Ford and GM do make decisions as to whether parts ar
available and for how long. I did own a 87 Chrysler 5th avenue for a
number of years and I would expect to be able to locate whatever I
would need for it. Might take some time but if the demand is there the
parts are usually available.

In another instance just this past year I needed a fan blade for a 64
Dodge PU and the Chrysler dealer bent over backwards to locate one for
me. Took a few days but they called when they had the blade and there
was no charge.

Bob AZ