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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...

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*jeep*+author%3Aclap&rnum=4&hl=en#acc61ce5c413e29d 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?

Reply to
Clap Trap
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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 >

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Reply to
Mike Romain

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

Reply to
Clap Trap

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

Reply to
Earle Horton

Reply to
L.W.(Bill) Hughes III

L.W.(Bill) Hughes III wrote in message=0D=0A...= =0D=0A=0D=0A> I get wound up easily and if sum1 sez summat I don't like= I hits or=0D=0A> pushes em i jus swing at em.My mum says that I hav a attitude= b'cos I=0D=0A> am quite strong and do alot of matial arts.She keeps havin= a go at me=0D=0A> n says that its gotta stop but I dont know how 2 stop= myself b'cos it=0D=0A> is only self defense and I neva hit first unless= they say sumat I=0D=0A> don't like but my mum doesnt understand.How can= I prevent myself as I=0D=0A> am only 12 and soon will hav lotsta ppl afta= me

Reply to
L.W.(Bill) Hughes III

Sorry - I meant zip as in zero.

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

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

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.

Reply to
Clap Trap

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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....

Reply to
Clap Trap

Reply to
L.W.(Bill) Hughes III

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.
Reply to
Clap Trap

Some coils will run on either voltage levels. My Accel Supercoil will run on 14+ volts or on the ballasted +/- 10 volts. Because I still have the Ford ignition module in there, I have to keep it at 10 volts.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

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