Re: Would a bad ballast resistor cause an 86 F250 not to start?

the engine wasn't that old, perhaps 7 years F.I.
Modern cars still do reduce voltage to the coils, mostly in the ignition
modal if I remember correctly.
The critical point being that during a start, the car pulls the available
battery voltage down to 9-10 volts, and a full 12v coil wouldn't have enough
voltage at that time to saturate and fire correctly.
It applied it the old days and still today.
Every starter test we do shows 9-10 volts at start and the car passes with
that number.


--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/


"Mike Romain" <romainm@xxxxxxxxxxxx> wrote in message
news:43B3F9F3.62C89578@xxxxxxxxxxxxxxx
> Like the man said, that is an old way of doing it and is not necessarily
> dependent on the coil.
>
> My 86 Jeep has the old Ford ignition and I bought an Accel SuperCoil for
> a hotter spark. The Accel coil can run on either a direct alternator
> power level or use a ballast system.
>
> I asked Accel about using it hot (14+ Volts) for the hotter spark and
> they told me if I did I would cook the ignition module. It even warns
> about that on the Accel site.
>
> You saw one old test engine. That does not translate to 'all' coils.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> Canadian Off Road Trips Photos: Non members can still view!
> Aug./05 http://www.imagestation.com/album/index.html?id=2120343242
> (More Off Road album links at bottom of the view page)
>
> Stephen H wrote:
>>
>> The class was free to me but the shop paid a couple hundred per tech
>> attending.
>> The test engine had sensors from all sorts of engines wired up to it, the
>> instructor could hit a few switches and cause all sorts of problems to
>> happen. Great learning experience.
>>
>> Restriction on the fuel filter? fuel pressure maintained constant, amps
>> increased and volume decreased. It was good to SEE the cause and effects
>> of
>> problems on the car.
>>
>> We did a voltage drop test one test lead on positive of battery and one
>> on
>> the hot of starter. Great tool for diagnosing many problems on a car.
>>
>> The instructor also did something to demonstrate the 10v system on the
>> coil
>> as it related to starting, but I don't remember exactly what at this
>> time...
>> Gust had another class on Volumetric efficiency in an engine and
>> diagnosing
>> the total fuel trim problems. (How much effect does a rear o2 sensor have
>> on
>> fuel trim...) That one flipped my learning around.
>> Got to find that book
>>
>> I'll now try to dig up the book with the wiring diagram; it showed 12 v
>> through the starting circuit to the coil and a separate line going
>> through a
>> resistor to the coil hot for running.
>>
>> If the coil stays with a constant 12 v while running than the chances of
>> killing a coil (primary side) from heat are much greater.
>>
>> Take care
>> --
>> Stephen W. Hansen
>> ASE Certified Master Automobile Technician
>> ASE Automobile Advanced Engine Performance
>> ASE Undercar Specialist
>>
>> http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
>> http://www.troublecodes.net/technical/
>>
>> "aarcuda69062" <nonelson@xxxxxxxxxxxxx> wrote in message
>> news:nonelson-B7FEEB.22001928122005@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> > In article
>> > <HlIsf.201681$qk4.35994@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
>> > "Stephen H" <hansensw@xxxxxxxxxxx> wrote:
>> >
>> >> Don't remember the class sponsor; was basic auto electronics class.
>> >
>> > Was the class free or did you pay to attend?
>> >
>> >> The instructor put a Volt meter on a 5.0 test eng and showed us.
>> >
>> > I suppose it would depend on where the instructor connected the
>> > volt meter. If he connected to the negative side of the ignition
>> > coil, then yes, I'd expect to see some fraction of system voltage.
>> > At the positive side of the coil, odds are that you'd see full
>> > system voltage.
>> > GM went this way in 1975
>> > Ford went this way with the intro of TFI, basically around 1984
>> > with the exception of carry over DuraSpark ignition used on HD
>> > truck applications and police cars thru the late 80s early 90s.
>> > ChryCo went this way around 1988 or so. Earlier on some models.
>> > Can't think of a single application offered in the last ten years
>> > that doesn't feed full system voltage to the positive side of the
>> > coil.
>> >
>> >> I'll have to look for the book. Was rather amazed when I quizzed my
>> >> father-in-law about it and he knew the answer but not the why.
>> >
>> > Not sure what the question was...
>> >
>> > The reason for a resistor in the ignition primary is to control
>> > current thru the coil primary. The anecdotal observation is that
>> > it also drops the voltage to the coil, but voltage is more or
>> > less meaningless until you have electrons flowing (current).
>> > Bear in mind, when the magnetic field in an ignition coil
>> > collapses, there is upwards of 300 volts induced into the coils
>> > primary windings. Knowing that, what difference could a few
>> > volts (10 vs. 12 vs. 14.5) make? None of this obviously should
>> > ignore the fact that voltage to the coil can fall too _low_ and
>> > affect spark output.


.

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