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Still chasing cause for failing points and condenser

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Still chasing cause for failing points and condenser

 
Old 06-10-2019, 09:06 PM
  #1  
RickDett
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Default Still chasing cause for failing points and condenser

1969 SB Coupe
I have other recent threads regarding this issue.

I toasted another set of points and condensers (that’s 4 this month) so there not “lemons”.

At this point I am trying to test the ignition resistor/ballast wire from coil to firewall I have it all disconnected at the firewall, coil and “R” on starter.

How do I test the coil resister/ballast wire?

What is the acceptable ohms range or measurement?

If it is out of spec can I purchase a new resistor/ballast wire?

Other notes:
At “+” coil I have
6 volts w/ key on, 12 volts with the points separated with thin cardboard
10.3 volts cranking
10.6 volts Engine running
Alternator Engine off 12.4 volts
Idle 14.4 volts after diving
Coil measures 1.5 ohms, secondary windings 9.09 ohms

Rick

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Old 06-10-2019, 10:06 PM
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TimAT
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Take a look at the Ignition sticky- it may have the answers you're looking for. It would be unusual for the resistance wire to fail giving too much voltage. Usual failure is they break and don't have anything.
I don't recall seeing anyone selling just that wire, but I have seen that wire bypassed with a ceramic ballast resistor. And for info, you are at the start point of the resistor wire- it runs from that point to the coil.
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Old 06-10-2019, 10:44 PM
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Voltage measuring over 14vdc "after driving" indicates that the alternator is over-charging the battery and at an excessive level. You may have some problem with the sensing wire which "tells" the alternator how much charge is in the battery. If that wire is restricting or blocking the actual battery voltage, the alternator will run at max output. This could cause your ignition issues.
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Old 06-10-2019, 11:22 PM
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Greg
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Hey Rick,
I know how frustrating this can be.
While I'm generally all for original equipment on these vintage Corvettes in most cases, have you considered the advantage of using the Pertronix pointless ignition? It installs in your factory distributor without modification and outwardly looks identical to the stock set up. I just installed this system in my '65 327 coupe.
Just offering an alternative. Good luck, Greg
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Old 06-10-2019, 11:34 PM
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ronarndt
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The ignition switch supplies full 12 volts to the points with the key in the "start" position. When you release the key and the switch goes to the "on" position, the voltage to the points should drop to approx. 9 volts to increase the life of the points.
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Old 06-11-2019, 02:50 PM
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Originally Posted by ronarndt View Post
The ignition switch supplies full 12 volts to the points with the key in the "start" position. When you release the key and the switch goes to the "on" position, the voltage to the points should drop to approx. 9 volts to increase the life of the points.
The operation of the ignition switch doesn't change whether it's in start/crank mode or if it's in "on" mode. The switch simply supplies 12v through a resistor to the coil primary windings. It's the starter solenoid R terminal that bypasses/shunts the ballast wire to restore the desired primary current level in the coil despite the lower battery voltage during cranking.

The points never see nine volts. When the points are open, they see 12-14 volts (battery or alternator source) across them. When the points close, there is zero volts across them.
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Old 06-11-2019, 04:57 PM
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Peterbuilt
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[QUOTE=RickDett;1599559991]1969 SB Coupe
How do I test the coil resistor/ballast wire?
What is the acceptable ohms range or measurement?]



This information is from my '74 service manual.

Are you changing the condenser with each new set of points?



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Old 06-11-2019, 06:06 PM
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Originally Posted by TimAT View Post
but I have seen that wire bypassed with a ceramic ballast resistor.
TimAT, That may come soon.


Originally Posted by 7T1vette View Post
Voltage measuring over 14vdc "after driving" indicates that the alternator is over-charging the battery and at an excessive level. You may have some problem with the sensing wire which "tells" the alternator how much charge is in the battery.
7T1, I do have a higher amp alternator installed rather than the standard one, could that be an issue?


Originally Posted by Greg View Post
Hey Rick,
I know how frustrating this can be.
While I'm generally all for original equipment on these vintage Corvettes in most cases, have you considered the advantage of using the Pertronix pointless ignition?
Greg, I actually have an old Mallory Unilite on stand by but it too requires a built in resistance wire.


[QUOTE=Peterbuilt;1599565023]
Originally Posted by RickDett View Post
1969 SB Coupe
How do I test the coil resistor/ballast wire?
What is the acceptable ohms range or measurement?]



This information is from my '74 service manual.

Are you changing the condenser with each new set of points?
Peterbuilt, Good info, I'll give it a test tonight. And Yes to changing the condenser each time.

Thanks
Rick
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Old 06-11-2019, 06:22 PM
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7T1vette
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The 'size' of the alternator makes no difference. The fact that it is putting out 14.4 volts (max output) AFTER driving it (battery should be fully charged) is something to resolve. Alternator output with a fully charged battery should be around 13 volts.
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Old 06-11-2019, 07:21 PM
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Could the problem be coming from the coil?
Maybe an internal short do to the coil failing?
Seems like something is burning the points.
I remember about 50 years ago I went through the same type issue on a big block Chevelle, but I can't remember what is fix was.
Dagnabbit!
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Old 06-11-2019, 08:41 PM
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Originally Posted by 7T1vette View Post
Voltage measuring over 14vdc "after driving" indicates that the alternator is over-charging the battery and at an excessive level. You may have some problem with the sensing wire which "tells" the alternator how much charge is in the battery. If that wire is restricting or blocking the actual battery voltage, the alternator will run at max output. This could cause your ignition issues.

NOPE- Chevy INTENTIONALLY did this-

http://www.madelectrical.com/electri...evymain1.shtml

""If cars would have been entirely built using all minimum engineering recommendations for copper cable gauge sizes, then these cars would be hauling around a few hundred pounds of very expensive copper cable. Since it was not practical to install so much heavy copper cable on the millions of cars built, Chevy engineering provided a practical exception to the rule.

At least one thing about wiring for this Chevy alternator system is very unusual, excessive voltage drop between the alternator and battery will occur with normal system function—and yet the electrical system worked fine. The battery charged perfectly and electrical system performance was not compromised in the least bit. It was a feat accomplished by the wiring system layout. Not only that, but it was a forgiving system that was more gentle to batteries and alternators in the event of recharging a battery while driving!

No doubt those “rebel with a cause Chevy engineers” who came up with this system knew exactly what they were doing. Truly the Chevy wiring system was unique. The design caused the voltage regulator to take voltage reading from the main power distribution hub (the splice). The heavy cable and minimum voltage drop recommendations from DELCO would have worked, even without special attention to where the voltage regulator would take voltage level reading.


When current flow through long wires is a large amount, a “problem” with significant voltage drop will occur. But regarding voltage drop at the long length of “alternator output wire,” the system was self-compensating. The regulator took voltage reading from the splice, which distributed alternator power. (“Voltage-Sensing was not from the alternator or the battery!) The regulator adjusted alternator output as required to maintain proper voltage level at the splice. Therefore a little voltage drop in a long wire from the alternator did not reduce system performance. The alternator did not mind producing power at 15.2volts, which allowed for a 1volt drop in the long wire, to arrive with power at the “splice” at 14.2 volts level.

This part of the system layout did not happen by chance. The voltage sensing wire from the regulator was connected where it would optimize system performance, which let the main hub distribute power at 14.2volts. It was a wiring design created with definite purpose in mind. Thanks to some clear thinkers at Chevy engineering department we were spared some cost, and weight, and bulky cables at the front of these cars!"

Originally Posted by Greg View Post
Hey Rick,
I know how frustrating this can be.
While I'm generally all for original equipment on these vintage Corvettes in most cases, have you considered the advantage of using the Pertronix pointless ignition? It installs in your factory distributor without modification and outwardly looks identical to the stock set up. I just installed this system in my '65 327 coupe.
Just offering an alternative. Good luck, Greg




I've installed this piece an several Corvettes...
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Old 06-11-2019, 09:50 PM
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Not sure what the difference is between primary, secondary or ignition resistance, but the wire from coil to firewall (all disconnected including at the “R” on starter) I get a reading of 1.6 ohms.

Is this an acceptable reading?

Maybe I should change out the alternator??


Rick
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Old 06-11-2019, 10:39 PM
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Originally Posted by RickDett View Post

Maybe I should change out the alternator??


Rick
There is nothing wrong with you alternator....
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Old 06-12-2019, 12:16 AM
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Sorry Rick,
I should have elaborated on that point. If you get the correct, matching coil from Pertronix, which externally looks the same as the original GM coil and fits right in it's place, you do not need to run any resistance wire. Just a direct 12 volts. It is a very foolproof system.
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Old 06-12-2019, 12:41 AM
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CanadaGrant
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I believe that your 10.6 volts through the cloth covered fuse box to coil resistor wire on a 69 is too high. I had about 7.8 on mine (69 427/390) before I changed it out from points to pertronix.

Last edited by CanadaGrant; 06-12-2019 at 12:44 AM.
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Old 06-12-2019, 07:15 AM
  #16  
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Are you sure you get 0 volts with key off? I think 14.4 at idle is fine. Alternators-regulators put out 1 voltage. The amps go down as the battery volts come up.
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Old 06-12-2019, 09:17 PM
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My two cents here. I agree with some of the posts, and disagree with a couple others. (I'm just mentioning those whose comments I agree with in this thread.)

I agree with:

TimAT: The ballast wire is rarely, if ever going to fail in a shorted mode. An open is more likely. And that doesn't seem to be occurring here.

7T1vette: The battery voltage does seem to be a bit too high. IIRC, the Delco alternator regulator has a negative temperature coeffcient thermistor in the circuitry that reduces the alternator setpoint/output voltage as the system (the alternator, and usually, the battery in non-Corvette applications) warms up from engine compartment heat. I would expect the battery to be closer to the mid thirteen volt range rather than mid fourteens.

OldCarBum: I have some questions about the coil integrity too (the coil can measure correctly ohm-wise, but be faulty inductance-wise), but doing some quick back-of-the-envelope calculations doesn't show me any obvious issues that would quickly ruin multiple sets of points (I do see some issues that would wear them out quicker, but probably not as quick as the OP is experiencing).

CanadaGrant: I agree that the 10.6v reading of the averaged voltage on the C+ line seems a bit high. Without seeing the actual C+ voltage waveform on a 'scope though, I can only make a guess here.

Summary, I'm not comfortable with the warm/hot mode voltage output of the alternator. I also think it would be productive to swap an old junkyard can coil into the system and see if the points damage still presents itself.
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Old 06-12-2019, 09:59 PM
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Originally Posted by derekderek View Post
Are you sure you get 0 volts with key off?
Yes
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Old 06-12-2019, 10:03 PM
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I ran two more tests


1. A reading at the "R" on the starter once the engine was running, with out the wire attached. I get .015 volts I assume that's virtually the same as zero.


2. Another reading with the single red power wire removed from the alternator. I get 9 volts at the positive coil down from 10.6 volts while the engine is at idle.


RIck

Last edited by RickDett; 06-12-2019 at 10:05 PM.
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Old 06-12-2019, 10:19 PM
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Originally Posted by 69427 View Post
It's the starter solenoid R terminal that bypasses/shunts the ballast wire to restore the desired primary current level in the coil despite the lower battery voltage during cranking.
I'm not sure I follow you, could you reword or further explain?

Rick
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