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How to check signal to coil - need help

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I'd like a simple way to see if my distributor pickup is sending a signal to the coil to generate a spark.


I'd like to use a simple test light. I ran my coil without a ballast between the run battery and it overheated and burned out. I now have the old Coil with a ballast between the run battery from the ignition with the start battery going directly to it for cranking purposes only.


Problem is I'm not totally sure this coil is any good. I've got 1 dizzy and 1 distributor with the single internal pickup that requires the remote electronic box(which I don't have) and an HEI unit I purchased new 7 or 8 years ago.


I'm looking for a place to put the signal light that can tell me if the distributor is signalling the coil to send a spark back to the rotor/cap.


I have it set up for the chevy HEI to control the spark at the moment.

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Test the coil....


Connect a wire from the -coil terminal to the - battery terminal. Put a coil wire in the top of the coil and hold near ground. Connect a wire to the coil+ terminal and  touch to the battery + terminal briefly. When you break the connection the coil wire should spark.



Wire the HEI like this...




Start engine. The EI unit in the dizzy can't 'burn out' just because you fried a coil. If anything was going to burn out it would have been the remote ignitior and you replacing it with an HEI unit. So test the coil and if good, wire it up.


The best thing is to get a '79 or newer coil (as in the diagram) and forget the ballast resistor. This will give you the full extra voltage the EI is capable of.

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The pickup won't light a test lamp. All it does is generate a week pulse. The ICU amplifies it and creates the voltage signal with enough current to fire the coil..


To test the pickup, see Testing in the factory service manual. The two pickup wires should read a certain resistance. And using an analog voltmeter, should waver while cranking.

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Disconnect the pick up coli. Connect a volt meter set on X10 RESISTANCE range to the coil leads. You should read 750 ohms. Far less or more is no good.


Now take the coil wire off so the engine will not start. Set the volt meter to 2.5 volt AC and crank the engine over. The meter should deflect slightly during cranking.


I see no reason to bother with this just wire it up and go.

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Forget everything you know about the distributor "signalling" the coil to make a spark.


Any coil of wire, especially one wrapped around a piece of iron acts kind of like a flywheel, when voltage is applied to it.  When you connect electricity to a coil, the current slowly builds to maximum.   This is like connecting an engine to a big flywheel, but instead of making a flywheel rotate, you build a magnetic field.   After the magnetic field is built, maximum current will flow.  This is why a points coil get hot when you leave the key on. 

So now you have a coil, witha big fat magnetic field, doing nothing but getting hotter.   You disconnect it.  The magnetic field collapses quickly.  When the magnetic field collapses, it generates a voltage trying to keep the electricity flowing.  This voltage is much higher than the voltage in the primary (battery) side of the coil.  Remember that big flywheel the engine got spinning?  Disconnecting a coil carrying electricity is pretty much like shoving a crowbar into the spokes of the flywheel.  There is alot of energy that has to go somewhere.


Hope you understand my poor explanation of how a coil works.


Every ignition system I have seen, from points on a 1948 Ford tractor, to the latest computer controlled coil on plug ingition system, works the same way.  A coil has positive, or hot, applied to it.  There is a switch that connects the coil minus to ground.  This switch is controlled by the engine, or the engine's computer, and when it is time for the coil to fire, the switch is opened, or turned off.


Points, you can understand is a switch.  A "matchbox" is just a switch.  A remote ignitor is just a switch.  The GM HEI is just a switch. 


One last thing about a matchbox distributor.  It is designed to "switch off"  if it is not getting a signal from the rotor in the distributor.  but it turns back on as soon as the distributor rotates.


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This is just what I needed to assure I'm good.  Thanks a bunch guys.  It will be a day or two before I get that far as I'm replacing the Head I was gonna use due to coolent leakage between the block and head before I even Got the engine started.


I am going back with the W58 head I had reworked a few years ago, but very few miles ago.  It's probably a blessing the engine didn't fire up when I tried to crank it. The one thing this motor has always done if fire up on the 1st revolution as long as there's gas.


Here is a pic of where Im at this weekend,,,,







So it's ready for the W58 head I know is flat on the bottom. Got to get a couple gaskets tomorrow, replace a valve I had robbed from the W58 and hopefully by monday I can put this truck back on my insurance, get a new tag and go from there. I'd rather have a coil that doesnt require the ballast and will get one soon. 




Bellow is the only pic I've got of the HEI but I had all the wiring complete before I noticed the leak between the block and head on the U67 head. I may take it by the shop that did the W58 and see whats up with it down the road.




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when you pput the head back on dont be afriad to move the cam abit to get the marks on chain to line up. I think rotate cam ccw will induce more slack in chin to lift the sprocket up.

It wasn't very difficult. With it being a new chain I was a little worried my self. It was very close to slipping on so I pot a 3/8th extension through the cam bolt hole to give myself just enough leverage to slide it on. 


The tool  worked great but be careful pulling it out with the wire attached to the top as it is a weak point. I could see someone breaking the plastic loop it goes through if that was your only means of sliding it out. I also was able to go in through the sight cover on the front of the head with a large screwdriver to help leverage it up while pulling on the wire and after inspecting it, the plastic loop it goes thru looked like it came close to the breaking point.


I did have it shoved down hard enough to pin the chain against the sides of the chain guide as well as deep enough to reach the bottom where it should be.


It is well worth the money 13.95 shipping included. Others I think have found it for about 10 dollars.

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