4 cylinder ignition ballast resistor

4 cylinder 153 Chevy ,12 volts,points ignition.It has a ballast resistor....1.8 ohm ballast,1.5 ohm coil....should be about 7-9 volts at the coil positive when the engine is running?
I got 11-12 volts .The coil went bad. Got a new coil and 1.8 ohm ballast....Still 11.5 volts at the coil,coil goes bad.Ballast shows1.8 ohms...Tried a different coil,still the same,tried another ballast,still the same.Then I put two ballasts in series,dropped to 10 volts,you would think it be 5 voltsI',I'm using a Fluke meter for ohms and volts. Tried another meter,the same.
The car system voltage is a steady 14.5.The engine runs perfectly until the coil goes to ****..It ran for a year no problem,now it's haunted....

 

Here's a site with some helpful testing info.
http://randysrepairshop.net/general-motors-breaker-point-ignition.html

 

Thank you Mr Partsman....I tested it with the engine off and the meter sees 6.5 volts with points closed and battery voltage with points open......
I was testing with engine running like everyone says to do it... My Fluke digital meter must "stabilize " readings when the voltage fluctuates when running....
So two bad coils are coincidence?

 

Glad I could help in some small way. Two bad coils in a row would be unusual.

 

Yes, but it is what it is.......I posted this problem on several internet sites and got many detailed posts on what was wrong from supposedly experienced people. Not one mentioned testing as noted in your link....

 

To test the voltage drop of a resistor in the ignition circuit the contacts must be closed with current flowing. Either bump the engine until the contacts shut or check it with engine running.
A 1.5 ohm coil and a 1.8 ohm resistor would have a total resistance of 3.3 ohms.
3.3 ohms divided into your voltage of 14.5 volts would give us a amp flow of 3.3 amps in the circuit.
3.3 amps of flow x the resistance would give us a drop of 6.59 volts at the coil and another 5.94 volts at the ballast. A combined drop of 12.53 volts ( which is about factory specs for this system) The 12.53 drop would allow approx 2 volts to flow across the contacts. In actuality this number would be much lower as both the coil and ballast offers increased ressitance when heated up.
The idea is to have very little voltage flowing across the contacts when running. ( Usually less than 1 volt).

Your numbers are fine as is , the coils are defective ( normal for some of the jap stuff out there today)
I would suggest using the Bosch Blue coil ( like a VW Bug) found here ..

http://www.mooreparts.com/store/pro...t-Blue-Coil/?gclid=CLjo0L6XwLYCFZE-Mgod8zMAWA

Requires no resistor and i havent ever seen a bad one !!
This will stop your coil problems......

 

Math doesn't add up. Where did the 2 volts come from?

 

6.59 plus 5.94 = 12.53 volts. Engine running he stated he had 14.5 volts.
14.5 volts minus 12.53 = 1.97 volts ( or 2 volts )
Pretty typical reading. The final resistance is the calibrated ( finely stranded cable) is designed to drop the final small voltage as close to zero volts as it can be.
A typical scope test on a perfect system would only have a voltage at the contacts of .100 mv = long life of the contacts.

You really didnt think i would write a post with defective math did ya ???

 

Your amperage number is incorrect. 14.5 Volts / 3.3 ohms = 4.39 Amps
4.39Amps x 1.5 Ohms= 6.59volts 4.39 Amps X 1.8 Ohms= 7.91 Volts
6.59 Volts + 7.91 Volts = 14.5v . Sorry but I couldn't help myself..

 

Im no expert at all and maybe i missed it but did you check the ohms of the coil? I have a chevy 4 cylinder in my nova and have yet to change the coil because i read they take a different ohm coil than 6 and 8 cylinders and the one the parts store tried to give me cross referenced with the straight 6. I dont know if it matters much or what harm could come from it but may be worth checking.

 

GOOD CATCH , My main point was the change in voltage and current flow from a key on engine off position and the changes when the engine starts and voltage increases.
Hopefully this post has helped someone understand the relationship in one way or the other...

 

I had major coil problems. NAPA replaced 3 of them, and then I moved to the US Virgin Islands and NAPA would no longer talk to me. I Called Bubbas and he sold me a coil (He said it would be my last coil) Well he was right, never had a coil problem again. That was three yrs ago and the new owner is still driving. Iceman