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Coil will only need the 12+ volts off the "I" terminal of the solenoid during "start", then should back down to around 9V for run?

Having a similar issue on my GW, and what I found......if correct!
 
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Discussion Starter · #342 ·
Okay guys I am getting somewhere possibly. As jim stated at the beginning it could be timing related. I did a deep dive on timing after post nutter bypassing and saw that folks were using older distributors. Pre 1982 I believe. My research led me to the team rush upgrade and also modifying the centrifugal advance on stock distributers.

So I have a new NAPA distributor for a 1985, COULD I be running out of mechanical advance? The reason I ask is because those relied on the MCU that was removed for the nutter bypass. I adjusted the timing to 4* BTDC as an experiment and some of what I think is pinging went away. I was looking at some JeepHammer stuff but for me the pictures aren't showing up.

By the way, I will admit, I was reading the voltage on the coil wrong... The coil is getting 12v like it should. I was taking voltage from the positive terminal to the negative terminal on the coil... not the positive terminal of the coil to the negative battery post. whoops lol
 

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Well mathematically, It ain't working out. You have a mysterious voltage drop in some connection or device.
Did you check the zero on the ohmmeter before taking the resistance reading?
With those readings, you should be seeing 8.09 Volts at the coil.
However if the ICM is starting to fail or poor connection, that is giving you some extra resistance in the circuit which could account for the 5 volts you are seeing at the coil.

Also check the black wire going to the distributor. This is the ground connection for the whole system.
The power comes from the switch>>>Ballast resistor>>>>Ignition Coil>>>>>Green Wire to ICM>>>>>>ICM output transistor>>>>>>Black wire>>>>Distributor case >>>>> Ground.
Any extra resistance in any of those components past the ballast resistor will lower the voltage at the coil.
You could check the voltage drop anywhere along that path to see where the extra resistance comes in. Anything from the (-) terminal coil to distributor case should be close to 0 volts with ignition on and engine NOT running.
Not knowing what type of Solid State switching device is used in the ICM I could see up to a 0.6 volt drop in the ICM.

So check voltage at the (-) terminal on the coil (green wire)
Check Voltage where the green wire plugs into the ICM
Check voltage where the black wire comes out of the ICM
Check voltage on distributor case.

Voltage readings are more accurate than resistance readings.

...

By the way, I will admit, I was reading the voltage on the coil wrong... The coil is getting 12v like it should. I was taking voltage from the positive terminal to the negative terminal on the coil... not the positive terminal of the coil to the negative battery post. whoops lol
Now I'm really confused....
If you are seeing 5 volts from (+) to (-) on the coil. or around 2.9 amps. 2.9 amps across the ballast resister is then only 3.6 Volts.
Check that voltage across the ballast resistor.

But if you are seeing 12 volts From (+) to ground on the battery, then you are missing 7 volts from the (-) on the coil to ground or around 2.3 ohms resistance. That's a little high.

By the way, 2.9 amps through the coil will be a weak spark.
 

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Discussion Starter · #344 ·
@John Strenk is there a chance that the ICM grounds to the fender as well? I did some quick continuity tests and the ground wire from the ICM was weak on the tone. I am going to check voltages this weekend so I can spend time and open up the loom to see where things are going.

Thanks for the information in checking the ICM. If I have a poor ground, can I create a dedicated ground near the ICM?

I think I could solve this issue with by putting in an HEI... but Id like to figure this out
 

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Discussion Starter · #345 ·
Hey everyone! So I have some developing information about my spark issues. Turns out, every thought that was discussed turned out to be a problem!

Chasing the weak spark:
After taking @John Strenk's advice and trying to find the voltages in all the segments of the ignition system, the issue was poor connection at the connector... Apparently the little tabs that make the "click" and hold the connector together broke off and fell into the connector and was held in place by the dielectric grease... After removing the broken tab, the connector seated all the way and I had excellent grounds and received the expected voltages throughout the system.

Looking into timing:
@Jim1611 suggested that my timing was off. At first I denied this theory because I was running great after getting the proper spark. After taking it to work, the "valve rattling" got worse! So I grab a timing light to see what changed. I was set at 10* initial so I dropped it to 8* initial. Still the valve rattling existed. I grabbed a precise aluminum welding rod and found the true TDC. It turns out that the harmonic balancer may have shifted at some point in the Jeeps life. I estimated it being about 4-6*.

That being said, I took in account the 4-6* and set the timing to 4* BTDC. This should have really had me at 8* initial. All my other issues went away. No more rattle under load. So I set it to 6* (which would be 10*) and it runs way better than it ever has.

What a whirlwind of events... I just need to adjust the carb for the best fuel mixture. Because I assumed the balancer was correct, the timing was 4-6* more advanced so naturally I was running leaner. To offset the lean conditions, my mixture screws were wayyy out.

Thank you all for the input and things to check out. I'll update some more soon.
 

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@John Strenk is there a chance that the ICM grounds to the fender as well? I did some quick continuity tests and the ground wire from the ICM was weak on the tone. I am going to check voltages this weekend so I can spend time and open up the loom to see where things are going.

Thanks for the information in checking the ICM. If I have a poor ground, can I create a dedicated ground near the ICM?

I think I could solve this issue with by putting in an HEI... but Id like to figure this out
No, the case for the ICM is insulated from the circuit. There are some recommendations as to grounding the black wire from the 4 pin plug to ground at the case.
But if you fenders don't have a good ground, you can make it worse.
Normally the black wire runs all the way to the distributor before it is grounded. They certainly wanted to keep all the important circuits for the engine grounded on the engine.
A good idea to clean all the area around the distributor clamp to insure a good ground.

If you download the FSM, there is a series of test you can do to isolate any problems with the ICM.

Yes, an HEI will solve many problems.
 
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