Scrambler ignition woes (kinda long)

For those who don't recall, some time ago I upgraded my CJ-8's ignition
to the team rush TFI style. Here's a link to the thread...

http://groups.google.com/group/rec.a...c61ce5c413e29d

Anyway, it gave out on me this weekend and I'm at a loss to explain what
happened. Here're the details if anyone has suggestions.....

Drove to my destination, no problem.
Minor detail - when I turned the Jeep off and took the key out, it kept
running. I had to hold the brakes and stall the motor to kill the
engine. This has happened before causing me to replace the switch.
This switch is so new that I doubt it is a switch problem. Hmmm.

After being there for several hours, I got ready to leave and the Jeep
wouldn't start. It would crank and crank, but no start.

Checked for fuel delivery into carb - ok

Pulled spark plug and checked for spark - nada.

Aha said I, Jeep is brain dead. Typical for the motorcraft style brain.

Went to Autozone for a new brain, plugged it in, zip.

Checked for spark out of coil - nada.

Opened up the distributor cap just to have a look. Looked like the
contacts were burned pretty bad and the tip of the rotor was flaky -
like a well used spark plug. Odd, but nothing screaming major problem.

At this point I noticed that both of the wires going to the coil (hot
side and tach lead) were melted over a two inch or so span about 6
inches or so away from the coil. No other melted wires anywhere and no
other melting on these two. Definitely not like an overload. Also
checked all fuses at that point and none were blown. The only heat
source near the melted section is a heater hose. That shouldn't be hot
enough to melt wires. Also, even though melted, there were no shorts in
those wires.

At that point, I put the original brain back in and checked a couple things.

I got 12 volts at the hot side of the coil with the key in the on
position. That indicated a problem with the brain because there should
only be around 4-6 volts there until the switch is in the start position
at which time the brain is supposed to jump it up to 7-9 volts (there is
a ballast resistor in this system).

I put the new brain back in and rechecked the voltage at the coil.
Voltages were as expected.

I checked the resistance of the coil (between positive side and tach
terminal) and got zip. I had no idea what it should be.

I went back to autozone and got a new coil, cap, and rotor. The new
coil has .6 ohms between the positive and tach terminals. That seems to
indicate the old coil is bad.

But here's the concern... Just for grins before I go all the way back
to where my dead Jeep awaits (several miles and $$ of gas away) I
decided to take the brand new brain back to autozone and have it
checked. Their checker says it is bad.

So, 1) Is there any reason why a the old brain going bad would cause the
old coil to die? 2) Is there any reason why a bad coil would cause the
new brain to die? And finally, 3) Any idea why only a small section of
wiring would melt?

Small section of wiring burned? Don't you need a diode in that system's
power to make it work because it feeds the alternator's excite as
well?? A diode will pop now and then. If they are hanging two wire
strands together, vibration will kill them.

If the diode blows short, the engine won't shut down. That would imply
a ground loop issue to me overloading the diode.

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!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Clap Trap wrote:
>
> For those who don't recall, some time ago I upgraded my CJ-8's ignition
> to the team rush TFI style. Here's a link to the thread...
>
> http://groups.google.com/group/rec.a...c61ce5c413e29d
>
> Anyway, it gave out on me this weekend and I'm at a loss to explain what
> happened. Here're the details if anyone has suggestions.....
>
> Drove to my destination, no problem.
> Minor detail - when I turned the Jeep off and took the key out, it kept
> running. I had to hold the brakes and stall the motor to kill the
> engine. This has happened before causing me to replace the switch.
> This switch is so new that I doubt it is a switch problem. Hmmm.
>
> After being there for several hours, I got ready to leave and the Jeep
> wouldn't start. It would crank and crank, but no start.
>
> Checked for fuel delivery into carb - ok
>
> Pulled spark plug and checked for spark - nada.
>
> Aha said I, Jeep is brain dead. Typical for the motorcraft style brain.
>
> Went to Autozone for a new brain, plugged it in, zip.
>
> Checked for spark out of coil - nada.
>
> Opened up the distributor cap just to have a look. Looked like the
> contacts were burned pretty bad and the tip of the rotor was flaky -
> like a well used spark plug. Odd, but nothing screaming major problem.
>
> At this point I noticed that both of the wires going to the coil (hot
> side and tach lead) were melted over a two inch or so span about 6
> inches or so away from the coil. No other melted wires anywhere and no
> other melting on these two. Definitely not like an overload. Also
> checked all fuses at that point and none were blown. The only heat
> source near the melted section is a heater hose. That shouldn't be hot
> enough to melt wires. Also, even though melted, there were no shorts in
> those wires.
>
> At that point, I put the original brain back in and checked a couple things.
>
> I got 12 volts at the hot side of the coil with the key in the on
> position. That indicated a problem with the brain because there should
> only be around 4-6 volts there until the switch is in the start position
> at which time the brain is supposed to jump it up to 7-9 volts (there is
> a ballast resistor in this system).
>
> I put the new brain back in and rechecked the voltage at the coil.
> Voltages were as expected.
>
> I checked the resistance of the coil (between positive side and tach
> terminal) and got zip. I had no idea what it should be.
>
> I went back to autozone and got a new coil, cap, and rotor. The new
> coil has .6 ohms between the positive and tach terminals. That seems to
> indicate the old coil is bad.
>
> But here's the concern... Just for grins before I go all the way back
> to where my dead Jeep awaits (several miles and $$ of gas away) I
> decided to take the brand new brain back to autozone and have it
> checked. Their checker says it is bad.
>
> So, 1) Is there any reason why a the old brain going bad would cause the
> old coil to die? 2) Is there any reason why a bad coil would cause the
> new brain to die? And finally, 3) Any idea why only a small section of
> wiring would melt?

Mike Romain wrote:
> Small section of wiring burned? Don't you need a diode in that system's
> power to make it work because it feeds the alternator's excite as
> well?? A diode will pop now and then. If they are hanging two wire
> strands together, vibration will kill them.
>
> If the diode blows short, the engine won't shut down. That would imply
> a ground loop issue to me overloading the diode.

Hmm - no diode in this system. It's been fine for several thousand
miles without it.

A coil can heat up and short together internally. When you say that the
resistance across the terminals was "zip", do you mean a short circuit (zero
ohms) or an open (infinite)? The "brain" as you call it, is basically a
signal amplifier and impulse generator. Shorting the output, as with a
shorted coil, can burn it out. The brain, on the other hand, can deliver
excessive voltage to the coil, heating the windings and melting the
insulation, which is after all only shellac. Now you have a chicken and egg
problem. The only way to fix it, is to replace the coil and brain with new,
together. Does this system have a ballast resistor anywhere?

Mike is always blaming faulty grounds. Still, these are old vehicles with
rubber mounted bodies and engines. It wouldn't hurt to verify with your ohm
meter that everything is grounded properly. A continuity tester might be
better, because the light bulb with put some load on the grounds you are
testing.

Now about the "two inches of wires melted", is that just insulation burned
off, or copper strands melted together? This part is just morbid curiosity.

Earle

"Clap Trap" > wrote in message
...
> Mike Romain wrote:
> > Small section of wiring burned? Don't you need a diode in that system's
> > power to make it work because it feeds the alternator's excite as
> > well?? A diode will pop now and then. If they are hanging two wire
> > strands together, vibration will kill them.
> >
> > If the diode blows short, the engine won't shut down. That would imply
> > a ground loop issue to me overloading the diode.
>
> Hmm - no diode in this system. It's been fine for several thousand
> miles without it.

There are typically two to six diodes in every alternator:
http://www.autoshop101.com/trainmodu...timage/12f.jpg If
one leaks it will be feeding the ignition through the exciter side of
the alternator, like Mike said.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

Clap Trap wrote:
>
> Hmm - no diode in this system. It's been fine for several thousand
> miles without it.

L.W.(Bill) Hughes III > wrote in message
>...


> I get wound up easily and if sum1 sez summat I don't likeI hits or
> pushes em i jus swing at em.My mum says that I hav a attitudeb'cos I
> am quite strong and do alot of matial arts.She keeps havina go at me
> n says that its gotta stop but I dont know how 2 stopmyself b'cos it
> is only self defense and I neva hit first unlessthey say sumat I
> don't like but my mum doesnt understand.How canI prevent myself as I
> am only 12 and soon will hav lotsta ppl aftame

Earle Horton wrote:
> A coil can heat up and short together internally. When you say that the
> resistance across the terminals was "zip", do you mean a short circuit (zero
> ohms) or an open (infinite)? The "brain" as you call it, is basically a

Sorry - I meant zip as in zero.

> signal amplifier and impulse generator. Shorting the output, as with a
> shorted coil, can burn it out. The brain, on the other hand, can deliver
> excessive voltage to the coil, heating the windings and melting the

Which could explain why I measured 12 volts at the coil with the "dead"
brain.

> together. Does this system have a ballast resistor anywhere?

Yes. There is one that drops a 12v source down to 4-6v when the switch
is in the run position.

> Now about the "two inches of wires melted", is that just insulation burned
> off, or copper strands melted together? This part is just morbid curiosity.

Just insulation. And it really doesn't look "burned." There are no
"burn" marks, it just looks melted with no discoloration of the
insulation in that region.

Clap Trap wrote:
> For those who don't recall, some time ago I upgraded my CJ-8's ignition
> to the team rush TFI style. Here's a link to the thread...
>
> http://groups.google.com/group/rec.a...c61ce5c413e29d
>
> Anyway, it gave out on me this weekend and I'm at a loss to explain what
> happened. Here're the details if anyone has suggestions.....
>

A follow up for anyone who's interested...
Got 'ol Sparky running again today. Turns out the coil was for sure
fried. It was actually busted open. Replaced the coil, ignition
module, and the melted wiring section and it purrs like a kitten again.
Now if I could just find that HEI distributor I bought a couple years
back, I could slap it on to avoid a future brain death....

An exploded coil usually means there is no resistor and you're
cooking it with a full thirteen, fourteen volts. Put a meter on it.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

Clap Trap wrote:
>
> A follow up for anyone who's interested...
> Got 'ol Sparky running again today. Turns out the coil was for sure
> fried. It was actually busted open. Replaced the coil, ignition
> module, and the melted wiring section and it purrs like a kitten again.
> Now if I could just find that HEI distributor I bought a couple years
> back, I could slap it on to avoid a future brain death....

L.W.(Bill) Hughes III wrote:
> An exploded coil usually means there is no resistor and you're
> cooking it with a full thirteen, fourteen volts. Put a meter on it.

There is a resistor. The coil is getting 4-6 volts when the motor is
off and the key is in 'on,' 7-9 volts when the key is in 'start,' and
11-12 volts when the engine is running.