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post #1 of (permalink) Old 08-31-2006, 06:17 PM Thread Starter
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Ignition Module Testing/Specs

Still can't get my 84 Cj to start. Has always run like a top until a few days ago. No fire. 258, no ECM, Nutter Bypass, TFI coil, HEI module, MC2100.

What voltage should I be getting out of my ignition module? I don't seem to be getting enough voltage to the coil. I checked voltage at the module outputs. My stealth HEI has very weak voltage on all outputs (I seem to remember around 3 volts). I plugged in my spare module which is a stock Duraspark and I am getting 8.5 volts off each output. What should the voltage be off of each pin on the HEI and off of each pin on the Duraspark? Is there somewhere else I should be looking to solve this problem? I admit it, I'm stumped.
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post #2 of (permalink) Old 09-01-2006, 08:42 AM
 
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Re: Ignition Module Testing/Specs

Key in the 'Run' position, 12 volts at the module 'Red' wire.
Around 8 volts to the positive side of the ignition coil.

Key in the 'Crank' (solenoid kicked in) 12 volts at the module 'White' wire.

Coil should be throwing somewhere between 0.65 Ohm and 1.0 Ohm when you test for resistance between the Primary (Low voltage) terminals on the ignition coil.

Take the module to any of the parts stores, they should be able to test it for you.

If the coil is fried, run a fresh ground wire to your cylinder head(s).
The only thing that normally kills coils is a bad ground to the head.
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post #3 of (permalink) Old 09-01-2006, 01:30 PM
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Re: Ignition Module Testing/Specs

"""""""Around 8 volts to the positive side of the ignition coil.
Key in the 'Crank' (solenoid kicked in) 12 volts at the module 'White' wire."""""""


JYG - aren't you thinking Ford? That's a hard habit to get out of!

I think he said HEI, then he tried the Ford Module.
If it's HEI there should be 12 volts at the coil (+) - "IF" he's eliminated the ignition resistor like he should have.
If not, then the 8 volts.

White bypass wire - should no longer be there for HEI - Hmmm, wonder if it still is and is touching ground somewhere?

Key on, not cranking - when the module first gets power it essentially grounds the coil (-) (Tach Terminal) But in a few milliseconds the current limiter works, so the voltage at the (-) side of the coil will read 6-8 volts (It's in the idle mode, coil's charged, waiting to be released.)

Cranking it will drop a bit lower, depending on the meter used. It's "average" will read lower, or it will be bouncing between 8 and 0. Better to use a dwell meter - it should show about 10-12 degrees dwell at cranking.

If the above is OK -
Look very closely at the ends of the coil - the squared coils are better - higher output, but they tend to break down easier too. Look for any signs of grey or brown streaking - the colors of smoke - that indicates the coil's insulation is breaking down. The only cure is a new coil.

I'm not conviced and don't understand why coils break down from a bad engine/head ground, but if JYG has had experience with it, then do it. It cannot hurt, but if it helps it's good to do.


JYG - if the engine ground was bad, then wouldn't the starter be in trouble too?

If it was the head isn't grounded good to the block, then the spark plug current has trouble returning, (hard to think all those head bolts don't ground well). But usually the coil is mounted on the block anyway. (Or were those you've seen with that trouble had the coil mounted on the heads?)

The path the "secondary" has to take is through the plug, through the head, through the block, through the battery (-) to (+), then through the ignition switch back to the coil primary - where the bottom of the secondary is tied to the coil (+) terminal. A complicated route for sure! Tying the secondary back to the primary like that creates an "Autotransformer" or "flyback" - boosting the output.

I'm not challenging nor doubting, just wondering about the how and why behind it. You aren't the first place I've heard it, so you aren't alone.

Hmmm, wondering too - some battery (-) "ground wires run to the head to a handy bolt, but some run to a manifold bolt, some even go to a handy bolt on the block. I'm wondering if there's some kind of a relationship there too?
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post #4 of (permalink) Old 09-01-2006, 01:39 PM
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Re: Ignition Module Testing/Specs

And now we see why mixing and matching can end up be a nightmare. TFI/HEI parts are a good match IF you understand ignitions. If you don't understand ignitions, then mixing parts can become a nightmare.

KISS... Until you understand ignition concepts, keep things simple... either FOMOCO or GM.

Then, when the light of day hits, you can start to experiment. Otherwise you're just swapping in parts and causing yourself a huge headache down the road. If you're lucky, you'll be on the road, if not... you'll be 30 miles from the trailhead stuck up to the frame in mud scratching your head in wonderment.

Remember KISS... Keep It Simply Simple!
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post #5 of (permalink) Old 09-01-2006, 03:26 PM
 
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Re: Ignition Module Testing/Specs

My fault! [img]/ubbthreads/images/graemlins/mad.gif[/img]

It's the pain pills. I fell down the basement steps yesterday I'm going to be living on pain pills for a couple of days.[img]/ubbthreads/images/graemlins/crazy.gif[/img]
Landed on my brain (in the seat of my pants) and now the psychotic nerve is in full revolt!
That's what I get for skimming the post instead of reading it! Sorry guys.
--------------------------

"JYG - if the engine ground was bad, then wouldn't the starter be in trouble too?"

Nope.
Depends on where the ground is placed on the engine.
Head gaskets and Rust bolt sealer/anti-sieze/thread locker and years of built up crud will kill any chance of ground for the head.

Bad plug or coil wire will cause the ignition coil to fry it's self also.
Arcs out internally because the high voltage can't get through a bad wire...

Coil wire will cause it to fall on it's face all at once, but usuall a bad plug wire will kill the coil over time.

Sorry again about the brain fart earlier...[img]/ubbthreads/images/graemlins/ooo.gif[/img]
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post #6 of (permalink) Old 09-03-2006, 04:58 PM Thread Starter
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Re: Ignition Module Testing/Specs

Found the problem. The primary coil wire was separating at a point inside the loom. It was enough to give me 3.5 volts and the symptoms of a bad ground. I started pulling all of the wires out of the loom to find my problem and there it was. Not sure how it happened but I soldered and heat shrinked it and every other questionable wire I could find while I was at it. Reseated all of my grounds, added another ground to my stealth HEI (which I replaced). Put it all back together and it fired right up. Now my timing seems to be off a bit. Oh well, I'll take care of that tomorrow.
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