Voltage coming out of coil? - Team Camaro Tech
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post #1 of 16 (permalink) Old Jan 20th, 07, 05:07 PM Thread Starter
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Question Voltage coming out of coil?

What's the proper voltage that should be coming out of the coil on a stock points set-up?

I've got 12.60 going in & 9.50 at a 700 RPM idle going out to dist. When I raise RPM's to around 2500/3000, it goes up to 11.20.
Does this sound right?

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post #2 of 16 (permalink) Old Jan 20th, 07, 06:11 PM
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Re: Voltage coming out of coil?

you really can't read DC voltage across the points(neg side of coil), it doesn't work.

12.6 at the + side of the coil makes me wonder if you have a resister wire or ballast in the circuit, it seems kinda high.
What is your voltage at the battery with the engine running?





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post #3 of 16 (permalink) Old Jan 20th, 07, 06:18 PM Thread Starter
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Re: Voltage coming out of coil?

I'll check that voltage at the batt. first thing in the morning. 12.6 at + side of coil is too high? Hmmm. Wonder if I have my wires hooked up wrong.

I'm gonna run out there now, 20 MPH winds and all.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #4 of 16 (permalink) Old Jan 20th, 07, 06:26 PM Thread Starter
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Re: Voltage coming out of coil?

15.4 at the batt. while running. Dist. hooked to - side.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #5 of 16 (permalink) Old Jan 20th, 07, 07:34 PM
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Re: Voltage coming out of coil?

Quote:
Originally Posted by stevo camaro View Post
15.4 at the batt. while running. Dist. hooked to - side.
What is the battery voltage with the car not running? Both of your readings, 12.6 at coil and 15.4 at BAT while running are a little high. Your meter could be off a little

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post #6 of 16 (permalink) Old Jan 20th, 07, 07:51 PM Thread Starter
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Re: Voltage coming out of coil?

I'll go check that. Wonder if voltage being too high has burnt the points?

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #7 of 16 (permalink) Old Jan 20th, 07, 07:55 PM
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Re: Voltage coming out of coil?

I'd expect battery voltage to be between 13.5 and 14.5, and coil voltage around 6 or 7.
And yes, 12.6 volts at the coil will be a lil hard on the points.

If you have a mechanical regulator, there is an adjustment inside to set the voltage.
You could verify your meter by reading a "known" voltage, maybe a 9 volt batery, or the battery in your dailyu driver should be just over 12 with the motor off.

You might take a reading from a good ground, maybe your alternator case or neg battery terminal, to the regulator base. I once had a "high voltage" condition due to not having a good ground on the regulator. The reading should be ZERO.





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post #8 of 16 (permalink) Old Jan 20th, 07, 08:07 PM Thread Starter
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Re: Voltage coming out of coil?

Batt. is 12.25 while it's not running. I figured the high voltage reading to the bat. running was due to weak battery. Figured it was charging it back up. It was low.

My meter is good, checked that.

Good info to check. I'll have to wait till tomorrow for the regulator test.
Thanks

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #9 of 16 (permalink) Old Jan 21st, 07, 06:26 PM Thread Starter
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Re: Voltage coming out of coil?

Yeah, voltage regulater was bad. Testing this morning it was at 16.4.
Had a couple laying around and that was a waste of time.
Got 9 volts out of one and another wouldn't adjust below 17.60

Bought a new one and adjusted it to 14.25. Then I changed the dist. with good points in it and the engine ran smooth, miss is gone.
So it did fry the points.

But, I'm still getting between 11.70 & 12.20 to the pos. side of coil. Fluctuates with RPM.

Neg. side is between 7.0 & 9.0 to dist.

I'm leaving the batt. hooked while I'm gone this week & see if it discharges.
Could still have something else going on, not sure.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #10 of 16 (permalink) Old Jan 21st, 07, 06:36 PM
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Re: Voltage coming out of coil?

I'd guess / hope you've found your problem.

Assuming the factory resister wire is still in place, right?

Don't know that I've ever actually checked voltage at the coil pos on a running car with points, that could be normal what with the points opening and closing and all.

With the points stuck closed, coil voltage should be around 6 volts on the positive side and zero on the negative.

If you do this test, ground the negative with a jumper wire, and have someone else turn the key while you read the meter quick like. The coil, and even the resister wire will get very hot very quickly.





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post #11 of 16 (permalink) Old Jan 21st, 07, 07:02 PM Thread Starter
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Re: Voltage coming out of coil?

Thanks Jim. This vehicle is my 69 4x4 suburban. Same basic electrical system I Imagine. At first my factory tach was bouncing around above 2500 RPM. Started running rough & had a miss. Thought it was coming from tach maybe so I disconnected it. Problem got worse, now REALLY mis-firing, sputtering. I've burned points before in this, so when the fairly new batt. kept discharging after a week, I thought maybe there's current flowing thru the dist. or something while it's sitting. Or too much voltage to the dist.

Looks like the latter, with 16.40 or so going to the coil. I still need to see why the batt. is draining. Could it have been the regulator? I made sure I cleaned all grounds good too.

And I rehooked the tach & it ran smooth up tp 4500 RPM's. So that's good sign as well.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #12 of 16 (permalink) Old Jan 21st, 07, 07:10 PM
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Re: Voltage coming out of coil?

it could very well have been the regulator causing the battery to go down. Often it's the alternator. It's not the distributor or points.

Do the light test... get a 12 volt test light from a hardware or auto parts store, disconnect the neg battery cable, and connect the light in series, one lad on the bat neg, the other on the cable you removed. If the light glows, something is drawing power, start disconnecting stuff till the light goes out.





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post #13 of 16 (permalink) Old Jan 21st, 07, 07:43 PM Thread Starter
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Re: Voltage coming out of coil?

I'll do that, Thanks Jim.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #14 of 16 (permalink) Old Jan 21st, 07, 09:19 PM
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Re: Voltage coming out of coil?

Key on with points open, my manual says you need aprox 8 volts at the + side of the coil.

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post #15 of 16 (permalink) Old Jan 22nd, 07, 04:18 AM
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Re: Voltage coming out of coil?

My thoughts are:
1. Stevo, field relay may be stuck closed draining the battery. Use the test light between the battery cable, any one, and battery post, and unplug the field connector, light off, bad regulator, get a Wells VR715 regulator and problem goes away. If light still on, bad alternator/diode inside.
Remove BAT wire to alternator, light off, then bad diode.

However, you stated 16 volts charging, ext reg's will do this if too high adjustment when battery is hot or at operating temp. So with 16 volts, it shows alt is good, capable of producing most any amount of voltage until it melts.

External regulated charging systems are tempermental. One needs to figure in battery electrolite temperature for amount of battery charge, regulator temperature for voltage charge. I adjust charging voltage at the battery posts, as this is the correct place to measure. I start the car, let the engine run at 1500 for 15 minutes, I adjust for 13.5 volts at idle with headlamps on. Rev engine to 3000 and voltage should not be over 14.8 volts with lights off, including all accessories off.

2. Resistive wire measurements. If the points are open during measurement, then battery/charging voltage will be read as there is no current flowing, max voltage. Close the points, a reduced voltage will be read. Over time, the heat goes up, because current is being dissipated as heat, voltage goes down. Now, as the points open and close, a pulsating DC voltage waveform is made, the DMM is measuring a rough average DC voltage. The higher the rpm's, the higher the voltage measured. So, 6-8 volts at idle up to 9-11 volts at higher rpm.

A DMM is really the wrong tool to measure ignition voltage because the display does not react quick enough to show the flucuations. The better models of DMM;'s have an analog bar across the bottom of the display reacting in real time. The proper meter to use is the ever famous analog meter, the D'Arsonval meter movement, Simpsom 260, Triplett PSM-4, etc. An analog meter has a slow frequency response.

If you're going to troubleshoot an old circuit/equipment, use the test equipment from the same time period.

As said, just my thoughts.

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