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post #1 of (permalink) Old 08-24-2004, 09:48 AM Thread Starter
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what did i do now? spark questions

hi there

so, i had someone else stop by to help me with my 82 cj7 with a 258...hasn't been running in 2 years due to a rebuild of the jeep (not the motor though).

we were working on it saturday...getting a spark off the coil and into the plug...i know this cuz i would hold the coil wire up to ground and a spark would jump probably 3/4 inch and i would do the same with the park plug and i would get a spark. the sprak off the coil however did have the characteristic weak spark color of orange.

we were playing with the timing...trying all sorts of things (i'm off to find a timing light today...but that probably won't due much good until i get a spark again).

we also noticed a part of the wiring harness getting really hot. we narrowed it down to a red/green wire (or maybe it is pink/green) that comes off of a red/white wire from the ingition module leading to the red wire of the coil). it was getting so hot that it was melting the sheathing away so we replaced it.

we were getting the same spark after we replaced that wire.

i was adjusting the timing again this morning (i think we screwed it up on sat)...got it set the way i wanted...tried turning the engine over and now i'm getting no spark...

so any ideas of what i screwed up?

thanks
patrick
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post #2 of (permalink) Old 08-24-2004, 10:18 PM
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Re: what did i do now? spark questions

Spark at the coil but not at the plugs?


(BTT for ya)
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post #3 of (permalink) Old 08-25-2004, 09:08 AM
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Re: what did i do now? spark questions

The wire colors you mention don't match up with the '78 FSM, so this is just a guess. Did you replace any wiring during the rebuild? There needs to be either a resistance wire or an in-line resistor between the ignition switch and the coil. If that was replaced with a regular copper wire you'll send too much power to the ignition module. That can cause the module to fry and wires to overheat.
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post #4 of (permalink) Old 08-26-2004, 01:42 PM Thread Starter
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Re: what did i do now? spark questions

hi there

well, i looked again at the wire i replaced (a red wire with a green stripe)...of course right on it the thing says..."resistor wire do not cut or splice"...and yes i did cut it and put in a new wire...not of the resistor type

i haven't replaced/cut/spliced any other wires in the original harness that i'm using.

sow...that resistor wire i'm pretty sure feed two things...the red wire to the coil and the red wire to the starting solenoid.

now...when i look at the voltage at the coil on the green wire side with a fresh battery and the key on (but not turning the engine over) i got about 5.3V...if i'm measureing that correctly...thats way too low right...supposed to be up around 10 right? and that's with the regular copper wire spliced in for the resistor wire.

so...looks like i have to get a resistor wire to splice back in to feed the coil...is that the next step?

thanks
patrick
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post #5 of (permalink) Old 08-26-2004, 02:13 PM
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Re: what did i do now? spark questions

Well, you don't have to have a resistor wire. As I said, you can use a resistor. The '78 FSM says that the resistor is 1.35 Ohm. A parts houses might have resistor wire on a roll. They might also have a 1.35 Ohm ballast resistor that would work just as well.

While you're at the parts house, have them test the ignition module. There's a chance that it got toasted by overvoltage. That might explain the odd voltage readings you're getting, too.

As to that wire feeding the coil and the solenoid, not exactly. That terminal on the solenoid has battery voltage when the solenoid is engaged. That feeds current the other way, to the coil. That maintains the necessary voltaqge there when battery voltage drops while the starter is cranking. Basically it bypasses the resistor wire during cranking.
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post #6 of (permalink) Old 08-26-2004, 02:34 PM Thread Starter
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Re: what did i do now? spark questions

well, i went back and took a closer look...i found that my ignition module had been leaking a goo...seems to me that it got too hot

put my old ign mod on and got a better reading at the coil with the key turned to on (not start)...13 V...this is whe nmy battery is hook up to a charger and the battery reads 14.3V with the voltmeter. the value did jump around quite a bit though (although it did sittle on 13V)...i don't know if i have a poor voltmeter...not getting a good contact at the coil cap or what...

would it be correct to say then the purpose of the resistor wire between the coil and ignition module is to knock down the high voltage of the coil before it gets to the ignition mod?

or is that way off?

well, off to get a resistor or some resistance wire and a possible a new ignition mod.

patrick
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post #7 of (permalink) Old 08-26-2004, 03:34 PM
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Re: what did i do now? spark questions

If your ign mod was leaking epoxy, I wouldn't even bother testing it. Usually they go bad with even a sign of bubbling in the epoxy pack.

The resistor is there to kill voltage to the Coil when the key is not in the START position. This allows for longer ignition component life. You should see around 10-11V when cranking and around 7-8V at idle. You're getting battery potential voltage at the coil now b/c there is no resistor in the circuit.

It's not absolutely vital that the resistor be replaced, but you don't get any benefit from higher voltage in the OEM jeep ignition setup. You may as well just replace it.

RRich or Leve could probably tell you all about it.
post #8 of (permalink) Old 08-26-2004, 03:49 PM
 
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Re: what did i do now? spark questions

As mentioned previously, the resistor wire is there to knock down the voltage to the coil (& module?) when the motor is running. It is necessary to protect the ignition system, which was made to operate at voltages below 12 volts, as that is what is available when you are first cranking over the engine. Once the motor starts, and the alternator bumps up voltage to 14 plus volts, you key is in the run position, and the resistor wire feeds power now. With the Ford ignition, you need it.
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post #9 of (permalink) Old 08-26-2004, 03:52 PM Thread Starter
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Re: what did i do now? spark questions

hi there

what's a ballast resistor look like and how would i wire it in?

where would i put the resistor?

im guessing it would not be a good idea to splice in the resistance wire that i just cut out.

i can't seem to find anyone that carries resistance wire...

thanks
patrick
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post #10 of (permalink) Old 08-26-2004, 04:07 PM
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Re: what did i do now? spark questions

</font><blockquote><font class="small">In reply to:</font><hr />
would it be correct to say then the purpose of the resistor wire between the coil and ignition module is to knock down the high voltage of the coil before it gets to the ignition mod?

or is that way off?

[/ QUOTE ]

Way off. The purpose of the resistor wire is to get full voltage to the ignition module when the starter is cranking. (Huh? Yes!) The key is that wire from the solenoid to the splice and then to the coil.

The ignition module can be built to run off of any voltage the engineers decide to use. The problem is that there's a big variation in the voltage available. When the starter is cranking, battery voltage will typically drop to 10 volts. Once the engine starts and the alternator comes on line, the battery voltage comes back up to 14. So what they did is build the ignition module to run on 10 volts.

When the starter is cranking and battery voltage is down, current flows from the battery through the solenoid, then to the splice with the resistor wire, and to the coil, so there's battery voltage (10 volts) there.

When the engine starts you release the switch and the solenoid drops out, breaking that connection. Now battery voltage comes back up to 14, but it has to run to the ignition switch and through the resistor wire to the coil. The resistor wire drops the voltage from 14 to around 10, and the module is still happy.

When you replaced the resistor wire with a regular wire, you were supplying battery voltage to the coil, which is enough to toast the module.

The details might be off a little, but that's the concept.

And QUIT FOOLING AROUND WHILE THAT COPPER WIRE IS IN THERE! You're going to toast another module.


</font><blockquote><font class="small">In reply to:</font><hr />
what's a ballast resistor look like and how would i wire it in?

[/ QUOTE ]

They used to be a ceramic block about a half inch square and two inches long, with a screw terminal on each end, and a couple of mounting ears.

You would cut the wire you spliced it and put each end of the cut to a terminal on the resistor.

</font><blockquote><font class="small">In reply to:</font><hr />
where would i put the resistor?

[/ QUOTE ]

You can mount it anywhere it's convenient. They used to be on the firewall. It could be damaged by vibration, so on the engine isn't a good idea.

</font><blockquote><font class="small">In reply to:</font><hr />
im guessing it would not be a good idea to splice in the resistance wire that i just cut out

[/ QUOTE ]

No reason not to as long as you haven't damaged it and still have pretty much the full length - an inch or so shorter won't hurt. One problem is that it's a nickel alloy - essentially stainless steel - I think, that might be next to impossible to solder. You'll probably have to use a very good quality crimp connector. Maybe someone else will chime in on that.
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