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post #1 of (permalink) Old 07-06-2009, 12:50 PM Thread Starter
 
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Red face Ignition Problem (TeamRush)

Re: Starting problem
Quote:
Originally Posted by MyJeeps
Hello,

i used to use this forum all the time (5 years ago) and am trying to get my '79 304 CJ-7 up and running.

i saw your recent post for GhostBS and i thought maybe you could help me out. (i haven't been approved to post yet)

It ran fine 2.5 years ago, we moved it into the mountains and winter, and then just wouldn't start. Have spark, fuel, and compression (probably, will check tmrw). But i think something electrical is preventing starting.

A grounded test light to the positive coil lead glows on "Run", not during "Start". But the engine turns over and wants to start, then nothing when back to run. The external resister gets REALLY hot if left in "Run", and there is almost no voltage (less than 1 V) read on the coil side of that resistor. But enough to light the light, and seems to fire when at "Start"

Anyway, i know it's electrical but need some way to start narrowing down the problem.

Any help is much appreciated.

Thanks,

Scott...
When you get approved, and you haven't got running yet, throw up a post with my user name in the title so I can post up pics and diagrams....

Anyway,,
Since you don't have any power to the ignition coil in 'CRANKING',
That means the wire from the small 'I' terminal on the starter realy to the ignition coil postive terminal isn't delivering any current to the coil during cranking.

You should get a 'BRIGHT' light at the coil positive terminal when cranking.

---------------

DO NOT leave the ignition switch in the 'RUN' position for any longer than it takes to do these tests at the coil connector!

Leaving the ignition switch on for extended periods of time will not only heat up the resistor wire and coil,
but it can easily KILL the ignition module!

Always unhook the coil wire connector and do your testing at the connector and not the module,
This will save a lot of heating of the module and coil and resistor wire!

--------------------

To test your module to see if it's still working,
Disconnect the coil connector from the coil,

Hook your test light to the POSITIVE battery terminal.
And probe the 'GREEN' wire terminal while the engine is cranking...

If the light flashes, the module is still working.
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post #2 of (permalink) Old 07-06-2009, 01:00 PM Thread Starter
 
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Quote:
Originally Posted by MyJeeps View Post
To test your module to see if it's still working,
Disconnect the coil connector from the coil,

Hook your test light to the POSITIVE battery terminal.
And probe the 'GREEN' wire terminal while the engine is cranking...

If the light flashes, the module is still working.

Update=

i probed the light from pos. battery terminal to green wire terminal lead to coil: the light was on for 'Run" and then was definitely on (seemed to flash) while trying to start.

i believe this means the module is good.

i tested the spark from one of the plug wires yesterday and it seemed fine. Consistent and repeating spark.

The voltage before the coil resister reads @ 12v. The resistance of the resister reads @ 2 ohms. But the voltage after the resister (very hot, but won't do anymore) reads less than 1 volt. This doesn't seem good.

But the sparks are flying, and module is doing its thing. The coil resistance is primary about 3 ohms, secondary @ 9,000 ohms.

Suggestions welcome!
Assistance much appreciated.

Scott...
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post #3 of (permalink) Old 07-06-2009, 01:35 PM
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If you have 12 volts from one side of the resistor to ground, and 1 volt from the other side of the resistor to ground, the resistor or a connection to it is bad. It's feeding 1 volt to the ignition system which isn't enough to run the engine. But if you have 1 volt between the two sides of the resistor, that's low (it should be in the 3 or 4 volt range) but not too far from what it should be.

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post #4 of (permalink) Old 07-06-2009, 02:02 PM Thread Starter
 
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Just checked, with key to 'run' and resister cold: 11.6v going in, 0.7v coming out.

But it is creating a spark at the end of an ignition wire.

Should i try connecting without the resister? Or just replace.

Last edited by MyJeeps; 07-06-2009 at 02:04 PM.
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post #5 of (permalink) Old 07-06-2009, 04:34 PM
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Either the resistor is shot or the ignition system is drawing way too much current. I definitely would not try running without the resistor.

Disconnect one end of the resistor and then check its resistance with your meter. The '78 Jeeps used a resistance wire instead of a discreet ballast resistor. The '78 FSM says that the wire should have 1.35 Ohms. If you get a reading considerably higher than that, replace the resistor.

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post #6 of (permalink) Old 07-06-2009, 04:57 PM Thread Starter
 
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The resistor reads close to 2 ohms. That's why i haven't replaced it.

Anything else that would lead to the less than 1 v being read on the coil side of the resistor?
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post #7 of (permalink) Old 07-06-2009, 06:04 PM
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Quote:
Originally Posted by MyJeeps View Post
Update=

i probed the light from pos. battery terminal to green wire terminal lead to coil: the light was on for 'Run" and then was definitely on (seemed to flash) while trying to start.

i believe this means the module is good.
TAKE THE COIL CONNECTOR OFF THE COIL AND PROBE THE WIRE TERMINAL!

Once the coil connector is off the ignition coil, you can leave the ignition switch on longer and not heat up the coil or resistor wire.

With the COIL CONNECTOR OFF THE COIL,
Hook your TEST LIGHT TO BATTERY POSITIVE,
And probe the 'Green' Wire in the coil connector while cranking.
You will most DEFINITELY get a 'FLASHING' if the module is working.

If you leave the coil hooked up and do the test,
The coil works like a capacitor, and will cause the test light to 'Ramp On' and 'Ramp Off' instead of giving you a good, solid, quick flash.


Quote:
i tested the spark from one of the plug wires yesterday and it seemed fine. Consistent and repeating spark.
Then that tells me the ignition switch is getting current to the ignition coil, the module,

AND,
The distributor trigger, module and ignition coil are working as designed...

Quote:
The voltage before the coil resister reads @ 12v. The resistance of the resister reads @ 2 ohms.
But the voltage after the resister (very hot, but won't do anymore) reads less than 1 volt. This doesn't seem good.

TAKE THE COIL CONNECTOR OFF THE COIL!
The coil is a DEAD SHORT when the key switch is on,
And the engine IS NOT running!


With the coil connector disconnected from the ignition coil,
The resistor ('Red' wire) should show about 12 volts or slightly less.

With the coil connector disconnected, you should get a 'Dim' test light when your test light is connected to battery NEGATIVE and you are probing the 'RED' wire...

This is because when you are testing an OPEN circuit with a resistor, the resistor won't show up on a voltage test.

When you use a TEST LIGHT, the BULB is the load, and the resistor will show up since there is a current draw through it.

2 Ohms is fine for the resistor wire, especially if you were testing it with the coil attached!

Quote:
But the sparks are flying, and module is doing its thing. The coil resistance is primary about 3 ohms, secondary @ 9,000 ohms.
3 Ohms primary and 9,000 Ohms secondary is fine for the Jeep/Motorcraft coil.

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Last edited by TeamRush; 07-06-2009 at 06:06 PM.
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post #8 of (permalink) Old 07-06-2009, 06:14 PM
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Also, if you get less than 1 volt during cranking at the 'Red' coil connector wire...

Then the problem is obvious...
There IS NO CURRENT from the ignition switch directly to the 'RED' wire during cranking.

The current for 'STARTING' or 'CRANKING' comes from the starter relay on the fender well.

The starter relay will have a 'I' terminal ('I' = Ignition) and that 'I' terminal should be hooked up to the positive side of the coil...

And it should supply a full 12 volts during cranking!

----------------------------------

Check to see if you are getting 12 volts from the 'I' terminal on the starter relay during cranking,
and if not, replace the starter relay.

Check to see if there is large resistance between the connector for the starter relay 'I' terminal and the 'Red' wire terminal for the coil...
(Coil connector DISCONNECTED!)
------------------------------------------

Here is the same diagram for your ignition expressed two ways...


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post #9 of (permalink) Old 07-07-2009, 09:06 AM
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Since you asked for your answer from TR, I stayed out until he posted.

I think the problem here is that you got out the VOM without knowing what to expect.

The formula for the voltage across a coil is;

v = L di/dt


Nothing to be scared of here.

v is the voltage, L is the inductor value, i is current and t is time. The term di/dt is the change in current with respect to time. If there is no change in the current, di/dt is zero and the voltage is zero.

This formula is for an ideal inductor. Because your coil is made of wire, and wire has resistance, you have a combination inductor and resistor.

Using the values you measured, you had a 2 ohm resistance with a difference of 11 volts between the voltage measured at the two ends. Using Ohmís Law, we would calculate a current of 5.5 amps. Thatís not outrageous.

Multiplying the current by the voltage difference across the coil, we get a little over 60 Watts. Yeah, it would get hot just like a light bulb.


You asked about connecting it without the resistor. You ignition circuit, if wired correctly, does exactly that when you try to start the engine. It uses a connection from the starter relay to bypass the resistor when the starter solenoid is energized.


You say you are getting a spark. Is it a strong blue spark or a weak orange or yellow spark? If itís a strong spark, I think you need to look elsewhere for you problem.


If Iím reading this correctly,

Quote:
Originally Posted by MyJeeps View Post
It ran fine 2.5 years ago, ...
that it hasnít been run in two and a half years, dump the tank and get some new fuel in there.

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Those who understand binary and those who don't.
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post #10 of (permalink) Old 07-07-2009, 10:10 AM
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Quote:
that it hasn’t been run in two and a half years, dump the tank and get some new fuel in there.
Good catch. I didn't recognize the significance of that statement. Even if that isn't the cause of this problem, it would be a good idea anyway.

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