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-   -   Ignition/ coil/ points? (http://www.hotrodders.com/forum/ignition-coil-points-229448.html)

choirboy 02-11-2013 03:14 PM

Ignition/ coil/ points?
 
I need a little help and guidance on a problem i am encountering with my chevy engine. It is a small block with 3 two barrel carbs. I have had this setup for over a year, and have had same distributer, coil and resistor set up for several years. over 2500 miles.
As stated it is an early chevy distributor with points and coil. I was noticing a slight miss. i checked points and made slight adjustment and opened them up to .019. When I did this the car did not want to start at all. I played with it a little more and still no luck. I installed new points,condenser and rotor cap. Car started still running a little rough, but felt it might clear out once plugs dried out. I had previously put new plugs in before the points etc. Now car starts and after a few minutes it acts like coil is breaking up and the Car starts missing real bad. if I leave it sit it fires right up.
I have tried a few things: I replaced coil and resistor. When the key is in the "run" mode with engine NOT running the resistor reads 12.3 volts on one side and 7.2 on the coil side. when car is running I get readings of 14.3 on BOTH sides of resistor. I know these are simple wiring setups but I am lost.
I looked at distributor but dont know how to check if it is shorting out. When I do a continuity check from the screw terminal that goes to the points to the plate that points and condensor mount to I get continuity when points close. Is this normal?
Please guide me in the right direction. Thanks for any input.
Rick

T-bucket23 02-11-2013 03:41 PM

When it is running what is the voltage at the + side of the coil. It should be 9 volts or so if you are using a resistor or resistor wire. If the voltage is less than battery voltage when it is not running it should be less when running as well as the feed is the same. If it isn't you may have the alternator back feeding it some how.
Do you have a dwell meter. Unless you are real experienced with setting the points with a feeler gauge it is hard to get them set properly. Dwell should be 28-32*.
Also keep in mind that changing point gap also affects timing.

delawarebill 02-11-2013 05:37 PM

Points
 
when the points are closed u will get continuity. open no cont. with sw to on position u should be getting ~9 v. the only time u get a full 12v is IF u have the coil also tied to the starter and in the start position only.. and dwelling is better in my opion, if not alot easier. if u want to get rid of the points i suggest..
pertronix or mallory points replacement.. both have worked for yrs for me..

choirboy 02-11-2013 06:45 PM

thank you for suggestions. Again to clarify, my voltage reading at + side of coil is about 7.5 volts with the ignition in run position but engine NOT running. When engine is running the voltage is 14.2 which is the same reading I get on feed side of resistor. There is a wire that goes from coil side of resistor down to terminal on starter, I wasn't sure what that was for so I disconnected it, but voltage readings did not change. I will get a dwell meter, but keep in mind that car fires right up and runs great for 4 to 5 minutes then starts to break up. I am assuming that is because the 14 volts going to the coil and possibly points is overheating the coil and or condensor. I am baffled. I also unplugged the small wires going to alternator and took readings. The results still were the same voltage readings on both sides of resistor.

EOD Guy 02-11-2013 07:44 PM

If you are getting 7.5 not running and 14 running, that is your problem....... you are getting backfeed from somewhere or the ballast resistor has given up the ghost.

max out of the resistor should be 9 ish volts, if you're getting 14 you will or have burnt up the new coil and or points.

The wire coming from the starter's "I" terminal supplies the coil with a full 12v while cranking to aid in starting..... you need to hook that back up. Once the engine starts and the key goes to the run position the ballast resistor or resistance wire supplies the coil with 9 ish volts. The coil isn't rated for a full 12v all the time.

NAPA sells a ballast resistor for the old MOPARS, I've used them in the past and they work great.

choirboy 02-11-2013 09:41 PM

I checked the I terminal on starter and have 12 volts with key in run position. I would assume that should only be in crank position. Is that correct? I also disconnected all wires from the coil side of the resistor and am still getting the same voltage reading as on the feed side of resistor. I assume that means that the resistor is caput. What would ruin this new resistor? My ohm reading is 1.2 across the resistor terminals. I went to another car and got .7 ohms, I just dont want to keep hooking up resistors if I am burning them up. Thanks again for help. Rick

choirboy 02-11-2013 09:53 PM

Correction on last post. The wire at solenoid was NOT on the "I" terminal, it was on the other small terminal which I believe is the "F" terminal. That terminal has 12 volts while in "run" position. Car was already wired when I got it. I don't know how or why this problem did not surface before. I guess I will get ANOTHER resistor and try this again with wire attached to the "I" terminal. Any more input is greatly appreciated.

EOD Guy 02-12-2013 03:41 AM

You have an issue with your wires somwhere......

"I" terminal on the starter should have 12v in start only, dead otherwise. This terminal supplies the coil with a full 12v while cranking etc....

"S" or "F" terminal on the starter should have 12v in start only, dead otherwise. This terminal gets 12v from the ing switch when the key is in the start position and makes the solenoid engage which in-turn makes the motor spin etc....

Large lug terminal on the starter goes to the pos post on the battery

Braided bare wire on the other lg lug, is the pos feed to the actual starter motor

choirboy 02-12-2013 04:21 AM

OK thank you. It looks as though I am getting something goofy with my solenoid terminals. I wasn't sure about that "s" or "f" terminal. Last night when I checked it, I was getting 12 volt with the key on, not just in the crank mode. I will double check this again. Now it looks as though I burnt up my resistor, cuz I have 12 volts at both terminals all the time. Even with wires on coil side unhooked which I am assuming would eliminate any backfeed scenario.
Thanks, rick

delawarebill 02-12-2013 06:53 AM

resistor
 
a resistor is blow not short.. but i guess there's an exception to every rule.. ask yourself... does the engine start up fine??? if so remove the wiring from the starter to the coil !!!! and just run from resistor.. my bucket engine makes maybe 2 rpm's and starts right up.. so i do not use the starter wire to coil...

oldred 02-12-2013 08:00 AM

You should have two wires on the positive side of the coil, one from the resistor output and another from the "I" connection on the starter solenoid. The wire on the input side of the resistor should be full voltage with the switch in "run" with the output to the coil at about 7 to 9 volts and the wire from the solenoid should be "cold", basically it's only purpose is to bypass the resistor to supply the proper voltage for starting but it is "hot" ONLY in "start". If that wire (from the solenoid) is hot in "run" then that is your problem, this wire is supposed to be "hot" ONLY in the switch start position and dead at ALL other times. This wire will have to be disconnected from the coil when checking for proper operation, if left connected to the coil there will be a voltage reading from the resistor output.

To help understand how this works it's important to understand the purpose of the resistor which is to protect the coil from over-voltage. A 12 volt coil is actually designed to run on about 8 volts and the reason for this is because of voltage drop from starter motor load during cranking, if the coil was designed to run on 12 volts it would only get about 8 volts during start because of starter motor load dragging down the system voltage. Obviously the low voltage would provide a weak spark just when a hot spark is needed most, during starting. To solve this problem the engineers designed the ignition system to run on approximately the same voltage it would see while under the low voltage due to starter load. They did this by using the resistor or a resistor wire to drop the voltage when the engine is running to about the same as when it is starting. They then provided the system by-pass wire from the solenoid to by-pass the resistor and provide full system voltage (which will have droped to about 8 volts due to starter load) ONLY during the start phase but the voltage supply from that wire has to disappear when the switch returns to "run" otherwise when the system voltage rises after the starter is disengaged the coil will be in an over-voltage condition. This by-pass wire is necessary because without it the normally full voltage at the input side of the resistor would drop due to starter load during engine cranking and would result in even lower voltage on the out-put side of the resistor going to the coil, basically defeating the purpose of using the resistor in the first place.

Here is a good explanation of ignition systems and how they work, the first part deals in detail with points type and how/why the resistor is used/wired.

http://www.burtonpower.com/tuning-gu...n-systems.html

Bryan59EC 02-12-2013 10:55 AM

Quote:

Originally Posted by EOD Guy (Post 1645404)
"S" or "F" terminal on the starter should have 12v in start only, dead otherwise. This terminal gets 12v from the ing switch when the key is in the start position and makes the solenoid engage which in-turn makes the motor spin etc....


To check this correctly, you will need to disconnect the wiring to the + side of the coil.
If you leave the coil connected, that post will have voltage to it any time the engine is running or the key is on.

Disconnected from the coil-----you should be getting 12volts to the "I" terminal (or wire) while the starter is engaged----and nothing with the key off or key on and the starter not engaged

oldred 02-12-2013 11:14 AM

Quote:

Originally Posted by Bryan59EC (Post 1645528)
To check this correctly, you will need to disconnect the wiring to the + side of the coil.
If you leave the coil connected, that post will have voltage to it any time the engine is running or the key is on.

Disconnected from the coil-----you should be getting 12volts to the "I" terminal (or wire) while the starter is engaged----and nothing with the key off or key on and the starter not engaged




Yes the coil (+) from the solenoid needs to be disconnected but the voltage may (or may not depending on the starter load and battery size/condition) be less than 12 volts. The entire system voltage will drop due to the heavy load from the starter so the voltage may drop as low as 8 or so volts and still be correct. It will be correct if voltage is present while cranking but the voltage disappears when the switch is released to "run". Theoretically the voltage from the solenoid should be equal to or slightly greater than the output voltage of the resistor since it's purpose is to compensate for the drop in input voltage to the resistor that results from starter load, without this by-pass circuit the coil would not fire reliably due to low output voltage from the resistor resulting from low input due to cranking load.

T-bucket23 02-12-2013 03:06 PM

If the engine is running or not should not impact the voltage drop across the resistor. The voltage at the coil side of the resistor should always be less than the feed side.It sounds to me like the alternator is somehow feeding full voltage to the coil through another connection.
Start the car with the alternator disconnected and see if you still have a voltage difference across the resistor. If you do you need to track down how the alternator is back feeding.
Could be as simple as an incorrectly wired ignition switch.

An easy test would be to disconnect the everything from the + side of the coil except the wire from the resistor and run a temporary feed from the battery to the other side of the resistor and start the car. See if the voltages are normal (14 on feed side and ~9 on coil side)at that point. If this looks normal with the car running look at the second wire you had disconnected with the car running and see if there is voltage on it. There should not be. It should only have voltage while cranking. If there is voltage there you need to find out why. Could be as simple as the connection on the starter, which is where this should go is somehow shorted to the battery lug.

EOD Guy 02-12-2013 04:07 PM

All good advice above, except you do not have to disconnect the wires from coil to check the "S" wire.... it's only energized when the key is in start and it's only function is to supply voltage to engage the soleniod etc.......

The "I" wire will get backfeed from the resistor wire to the coil etc...... but it's designed to provide 12v to the coil so that shouldn't be an issue, however if it's not disconnecting from the starter solenoid feed then...... it makes sense that that's where the 14 volts are coming from...

Try disconnecting the "I" wire from the coil and see if you are getting voltage on the wire with the key in start, then turn the key to run and it should go dead...... if it's not, check and make sure the ring terminal on the starter end of the wire isn't making contact with lg lug with the battery cable at the starter...... which I suspect is your issue.


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