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Originally Posted by Deadman 94 xj
Thanks for the reply JeepHammer.
-When I say weak spark I just mean it's not very bright or snappy. There is a spark but it's not very impressive which I know is impossible to diagnose over the internet.
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'Strength' of spark isn't the issue,
The fact that you are getting spark is the issue.
That means the distributor is sending signal,
And the module is recieving it, and triggering the coil to fire.
All good signs.
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-The rotor was turning. I actually probed the 'carbon button' while the engine was cranking and got the same spark.
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Probing the carbon button is DANGEROUS! You can get a pretty good zap doing that while the engine is cranking!
(ask me how I know that!)
Check the plug terminals, if they are aluminum and corroded over, it's time for a new cap.
Aluminum gives up VERY quickly when spark energy smacks into it.
Brass terminal caps are ALWAYS the way to go... If you don't already have one.
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-I probed the engine block, distributor housing, and the module and all seemed to have good ground.
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Module wouldn't trigger and coil wouldn't fire if you didn't have a good ground,
But poor ground to spark plugs will cause the cap to go south that much faster,
And rusty/oil covered plugs/plug holes will kill a coil over time.
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-It wasn't running. I just got done replacing the rear main seal. I also swapped in a new set of spark plugs and adjusted my initial timing. It was running great for about a day.
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This is smelling a lot like a failure of the ignition coil or the module... Since each only had a few hours on it...
When you mounted the module...
Did you clip off the little plastic tabs on the bottom so the module set flat on the heat sink?
I'm wondering about the module now...
What did you use for a heat sink?
Did you use heat sink paste or that dielectric grease that comes with the module?
This one is a real puzzler, usually when someone does this correctly, there are no issues for years...
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The following day I went out to start it and it took forever to start but eventually it did.
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If it sat a while have you checked the fuel or the fuel pump/filter?
This is where one of those see though filters comes in REAL handy!
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I drove it to work that day, parked it and it sat for 8hrs. When I came out to start it it had the same symptoms of not wanting to fire, almost like it was flooded. Drove it home fine.
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That sounds like a fuel issue...
Slow to fire is almost always a fuel delivery issue, especially when you leave the vehicle set a while.
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Later that evening I went out to start it and nothing.
It just kept cranking.
I looked over the fuel system and then the spark and noticed no spark at the plugs.
That's where I'm at now.
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EXACTLY which coil are you using?
Factory Prestolite? Factory Ford? Ford E-core?
Reading and hands on checking EVERYTHING is the only way to learn anything, no matter what anyone says.
Looking for that 'Improbable' thing is what we do...
Someone getting a terminal loose on the wire, Someone pinching the insulation in the terminal so the wire isn't making good contact, finding that terminal that is corroded or not making contact with the terminal tab, ect... Looking for the improbable...
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The only thing I messed with while doing the rear main seal was the starter and it's cable. I did read in another post where a guy had his starter wire robbing the system of power. I know mine is in pretty bad shape but it's never given me a problem before but who knows.
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Starter will drop line voltage as it sucks AMPERAGE...
The line voltage should come right back up when you let off the starter...
As for voltage drop,
As you crank on that battery, it will discharge,
If you have a battery charger, slow charge the battery over night when you aren't working on it.
It's VERY POSSIBLE you got a bad module.
Bad modules usually show up pretty quickly, like this one did, if it's not bad out of the box, it will go bad in the first few days.... Crap happens since the 'Import' folks won't 'Burn In' test the components before they ship...
It's VERY POSSIBLE you have a bad coil. Not likely, but possible...
The only thing that usually kills a coil is a bad engine ground.
When the plugs can't properly ground, the spark energy will discharge where ever it can,
And with a bad coil wire or distributor cap, or bad ground to the engine heads,
The spark will discharge in the coil it's self and burn things up...
YOU ARE getting trigger signal from the distributor.
If you weren't, the module wouldn't 'Flash' when you test the coil 'Green' wire...
That doesn't mean the module is firing the coil correctly,
It just means the distributor is triggering.
The 'Cheapest' component in the system is the module at around $20...
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BEFORE I CHANGED IT,
I would check to make sure I had FUEL PRESSURE!
I'd let the vehicle SIT STILL for about 12 hours so if the fuel is creeping back to the tank, I'd know about it!
I'd take the fuel line loose from between fuel filter and carb, and I'd put a jar under the line,
Crank the engine about 30 seconds...
You should have more than a pint, less than a quart after 30 seconds of cranking with an open line.
If you have to crank a while to get fuel pumping, then you have found your issue...
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I would hook the fuel line up,
I would use some starting fluid in the carb then crank it.
If it fires right off, then the carb is leaking your fuel out of the float bowl while the vehicle sits still!
If it fires right off,
That means the ignition is doing it's job, and it's a fuel issue!
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Once you have ruled out a fuel issue, Which this sounds like, and the battery is charged,
Then it's time to review all your wiring in the ignition,
And time to replace that module.
The good news is, the module, coil, coil wire and cap/rotor is about all that it can be.
If you try these things, let us know and we'll continue to brain storm...
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Something that came to mind,
The last time I saw this, from this forum, I drove 2 hours to help the guy...
Turned out he used too much dielectric grease on cheap plug wires...
And the plug terminals backed off the spark plugs!
The grease allowed the boots to push the plug wire terminals right off the plug terminals and when they backed off far enough, it wouldn't fire!
I REALLY got zapped on that one since I figured it was the cap... When I put a test plug in the cap end of the coil wire, regular spark,
Put the coil wire on the cap... NOTHING to the plugs...
Wouldn't flash the timing light.
So I popped the cap, tested the center electrode, and SURPRISE! Plenty of current!
I was ringing electrons out of my arm for two hours!
Finally pulled a plug wire off the plug and it popped off with zero effort... Problem solved!
Not saying that's your problem, just letting you know that people doing this for years still overlook the obvious and get zapped once in a while!
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HEI, Weak spark at coil, no spark at plugs
) with the probe to generate a spark while cranking.
