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Unread 07-27-2011, 06:28 PM   #1
Deadman 94 xj
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HEI, Weak spark at coil, no spark at plugs

77, 304, Team Rush with HEI.



I'm getting a very weak spark at the coil and no spark at all at the plugs. Fuel is good, spark is bad.

I tested the HEI module to the best of my knowledge and it appears to be working correctly. One think I did notice is with the tester-light on the + battery terminal, and the probe on the GREEN wire at the coil, I'm getting no constant light. However, when the engine cranks I'm getting a consistent flash. Same symptoms at the 'C' terminal on the module.

When I test the RED wire with the key in the RUN position I'm getting a bright light. Same test but cranking, I'm getting a dimmer light. Both tests are consistent.


The only thing I'm left to assume is it's either the coil or the module. Everything appears to be grounded correctly.

The cap, coil, rotor and module are all about 8 months old. New plugs, no fouling.

I don't want to start throwing parts at it but I am going to head out and pick up a module since it's one of the things I'm not sure about. If it's not that, then the coil.

Any other ideas? Could something else be robbing the system of power?

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Unread 07-27-2011, 06:52 PM   #2
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The module is working, No constant 'On' light at the 'Green' or 'Coil' wire terminal is normal with an HEI, that's why they don't burn themselves up when you leave the key on.

If it's flashing when you test it while cranking, that means the module is getting signal, and it's switching the coil 'On & Off' like it should.

If you are getting spark at the coil, then the coil is working.
Don't know what you mean by 'Weak Spark' because everyone's version of 'Spark' is different without a spark tester...

My guess is, break in the coil wire or center terminal in the distributor keeping the spark from getting out to the plugs...

Did you check to see if the rotor is turning?
If the rotor is tuning with the engine during cranking, then it's not a distributor or camshaft gear...

Make sure your connections are good at the coil, at the module, ect.
Sometimes the connections LOOK good but aren't making connection...

Was this thing running then died all at once?
Is this a fresh start with they hybrid ignition?

What happened right before this problem started?
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Unread 07-27-2011, 07:03 PM   #3
Deadman 94 xj
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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.

-The rotor was turning. I actually probed the 'carbon button' while the engine was cranking and got the same spark.

-I probed the engine block, distributor housing, and the module and all seemed to have good ground.

-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.

The following day I went out to start it and it took forever to start but eventually it did. 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.

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.

I've been reading a lot!

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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Unread 07-27-2011, 08:18 PM   #4
Deadman 94 xj
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Well I replaced the coil wire for S&G and nothing. Like I said before, I am getting a spark at the cap but it seems weak to me. Is it possible that the coil could be not putting out enough spark to fire the plugs?

This is assuming the HEI module is good.
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Unread 07-28-2011, 02:10 AM   #5
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[QUOTE=Deadman 94 xj;11926853]77, 304, Team Rush with HEI.


When I test the RED wire with the key in the RUN position I'm getting a bright light. Same test but cranking, I'm getting a dimmer light. Both tests are consistent.

/QUOTE]

Looks like the wrong way round, you should have the dim light when in "Run" 6-7V and "Bright" light 12V in "start".

Did you swap some of those wires around on the starter and solenoid or break a connector?

You may have disconnected the feed from the solenoid and are only getting 6-7V in "Start" which will explain its relucatnce. You need to measure the voltage at the coil +ve wires to be sure.
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Unread 07-28-2011, 05:50 AM   #6
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Check your engine block ground.
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Unread 07-28-2011, 08:08 AM   #7
JeepHammer
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Quote:
Originally Posted by Deadman 94 xj View Post
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.
'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.

Quote:
-The rotor was turning. I actually probed the 'carbon button' while the engine was cranking and got the same spark.
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.

Quote:
-I probed the engine block, distributor housing, and the module and all seemed to have good ground.
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.

Quote:
-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.
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...

Quote:
The following day I went out to start it and it took forever to start but eventually it did.
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!

Quote:
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.
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.

Quote:
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.
EXACTLY which coil are you using?
Factory Prestolite? Factory Ford? Ford E-core?


Quote:
I've been reading a lot!
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...

Quote:
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.
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...

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

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...

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

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!

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

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...

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

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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Unread 07-28-2011, 08:23 AM   #8
JeepHammer
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Quote:
Looks like the wrong way round, you should have the dim light when in "Run" 6-7V and "Bright" light 12V in "start".
Not with his system, no resistor of any kind...
'Run' will be brighter since the starter isn't drawing a bunch of voltage from the battery,
'Cranking' dimmer because the starter IS drawing a bunch of current from the system.

Quote:
Did you swap some of those wires around on the starter and solenoid or break a connector?

You may have disconnected the feed from the solenoid and are only getting 6-7V in "Start" which will explain its relucatnce. You need to measure the voltage at the coil +ve wires to be sure.
BagusJeep,
I know you are trying to help,
But read the orignal post,

Jeep/Motorcraft distributor from '78 to '91 Jeep,
Distributor has the 'TeamRush' upgraded cap, rotor, plug wires,
GM HEI style module,
Coil unknown, An E-core coil would be best with the HEI style module, but not a 'Requirement'...
As long as he didn't use the '74-'77 Prestolite coil, the HEI module will do fine with anything else.

Take a look at this graphic,
He's used the better Jeep/Motorcraft distributor,
He's used the upgraded Tall Rotor & Larger Cap,
He's switched to the better high voltage plug wires,
ALL CORRECT for better ignition.



He's gone with a HEI style module instead of the trouble prone 'DuraSpark' style module.
More reliable and cheaper on the front end, fair choice...

The Jeep/Motorcraft distributor is a good, solid choice without busting the budget, around $50 for a reman.

The upgraded cap, rotor, plug wires are replacment parts off the shelf, so they are no more expensive than regular 'Tune Up' parts for the Prestolite that was in there, and about 100 times better in design and function than the Prestolite components...

The only question is the ignition coil... and if he used a brass terminal cap or not...
Brass doesn't corroded over right away torturing the spark energy to find a conductive spot to get through to the plug wires...
And the factory Prestolite coils had a REALLY crappy winding ratio, weak connections at the terminals, weak insulation, ... they are weak all the way around...,
Trouble prone and generally a good idea to replace when you get the chance...

Every part of the conversion he did was chosen for it's RELIABILITY with a reasonable COST in mind...
HEI style module, Off the shelf distributor, off the shelf cap/rotor/plug wire upgrade/off the shelf module upgrade, ect....

Everything is an UPGRADED part in every way when doing this on an AMC V-8 engine with a Prestolite ignition ('74-'77)...
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Unread 07-28-2011, 08:35 AM   #9
Deadman 94 xj
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Quote:
Originally Posted by JeepHammer View Post


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!)
What I'm describing as the carbon botton is the little 'nipple' on the inside of the distributor cap. I used my tester with the gator clamp on the (-) battery terminal and then probed the botton/nipple with the probe end while my wife cranked the engine. I got VERY little spark doing this. I mean I almost had to rub the nipple ( ) with the probe to generate a spark while cranking.

Quote:
Originally Posted by JeepHammer View Post

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.
I'm using the MSD cap-adapt as per your instructions.



Quote:
Originally Posted by JeepHammer View Post

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 is kinda what I'm thinking too. As far as the module placement, I followed your recommendations to the 'T'. It still had the heat sink in there from radio shack and there is even dielectric grease on the terminals still. It all looks pretty clean.

Quote:
Originally Posted by JeepHammer View Post

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!

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.
This is what I thought initially. I checked the carb and saw that fuel was squirting into the bowls. I thought maybe it was flooding out so I replaced the fuel filter and made sure my return line was clear. I actually got a mouth full of fuel while doing that! But all is clear in both directions.

I guess it could still be flooding with a bad flaot or something but the no spark at the plugs is what's getting me.

Quote:
Originally Posted by JeepHammer View Post

EXACTLY which coil are you using?
Factory Prestolite? Factory Ford? Ford E-core?
The coil is the MSD 8227 TFI coil. If it is the coil I have to figure out why it went south so fast see as how it's only about 8 months old.




Anyway, I'm going to play with it some more and determine if I want to replace the coil or the module first. I think having two modules might not be a bad idea.


Thanks again for your help!

No comment on zapping yourself
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Unread 07-28-2011, 09:27 AM   #10
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Quote:
Originally Posted by Deadman 94 xj View Post
This is what I thought initially. I checked the carb and saw that fuel was squirting into the bowls. I thought maybe it was flooding out so I replaced the fuel filter and made sure my return line was clear. I actually got a mouth full of fuel while doing that! But all is clear in both directions.

I guess it could still be flooding with a bad flaot or something but the no spark at the plugs is what's getting me.
Don't know what carb you are running,
But looking to see if it's 'Squirting' fuel doesn't tell you anything....

Since the float bowls can be drained, but still have fuel in the accelerator pump to give you a squirt or two...

The fuel line fuel flow test...
And starting fluid test is the best way to determine if it's fuel or ignition...

It's a quick test, not hard to do and will rule out fuel pump, carb, ect. right away.

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

Using a 'Test' plug and a spark plug wire instead of coil wire will rule out the cap, coil wire, ect.

Spark plug wire attached to the coil,
With a GROUNDED spark plug in the spark plug wire, crank the engine, see what you get at the spark plug gap...

This will tell you if your spark energy is getting out of the coil or not.
If it IS getting to the test plug,
You are narrowing things down to the coil wire, cap, rotor...

If you aren't getting good spark at the test plug,
Then you can work backwards, coil, module, ect.
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Unread 07-28-2011, 09:47 AM   #11
Deadman 94 xj
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Ok, I'll retest the coil tonight. I do remember testing it before with a test plug and getting a spark at the gap. I'll have to do it again to see what the arc looks like.


The carb is the MC2100. I can check with the starter fluid just to rule it out for good but either way, I'm not getting spark at the plugs.

Thanks!
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Unread 07-28-2011, 11:15 AM   #12
JeepHammer
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Swap a spark plug wire for the coil wire when you test with starting fluid.
This will rule the coil wire out while you are testing.
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Unread 07-30-2011, 12:13 AM   #13
Deadman 94 xj
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It's alive!

It was the coil I just put in 8 months ago. As soon as I plugged in the new one it fired right up. I used the same MSD coil for the new one since I didn't feel like shopping around and making a new bracket. Lets hope this one lasts a little longer.

Thanks for all the help!
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Unread 07-30-2011, 08:49 AM   #14
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Glad to hear you are up and running!
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