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'86 V-6 Voltage Question

Sleepwalker

Contributing Member
Hi-
1986 v-6, points ignition, external coil resistor.
I have been tracing the electric current flow in my no start situation and had a couple questions. Voltage tests fine from the battery to the starter solenoid, to the circuit breaker up to the instrument panel to the Ign terminal. All 12.4 V, same as at battery. When I trace it back thru the harness to the coil resistor, the voltage has dropped to 11.4 . Is this a problem? (might not be the cleanest contact) On the other side of the resistor the voltage is 10.0V, and this is also the voltage at the + terminal on the coil. (which should be about right I guess).


Also there is no voltage indicated on the coil wire end going to the distributy. with the switch in the "on" position. What would cause that? It is a new Sierra coil.


Thanks, Rich
 
Ayuh,..... Did you file, or change the points this year,..??

If not, that's most likely the cause of the no start,.....
 
Thanks. You know, I did give them a swipe some fine paper. And was thinking about this last nite...should I see voltage from the coil wire when the points are open or closed?
 
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Hi-
1986 v-6, points ignition, external coil resistor.
I have been tracing the electric current flow in my no start situation and had a couple questions. Voltage tests fine from the battery to the starter solenoid, to the circuit breaker up to the instrument panel to the Ign terminal. All 12.4 V, same as at battery. When I trace it back thru the harness to the coil resistor, the voltage has dropped to 11.4 . Is this a problem? (might not be the cleanest contact) On the other side of the resistor the voltage is 10.0V, and this is also the voltage at the + terminal on the coil. (which should be about right I guess).
You should have what's called a "start-by-pass" circuit.
This circuit will provide full voltage to the ignition coil (by-passing the resistor) during starter motor activity.
In other words, while the starter motor is operating, it circumvents the coil's resistor circuit as to ensure coil function when the starter motor is taking the voltage down.

Two ways that we will see this done:
..... starter motor S circuit triggers a relay that will in turn provide full un-resisted coil voltage.
..... starter motor solenoid R or I terminal provides full un-resisted coil voltage.


Also there is no voltage indicated on the coil wire end going to the distributor. with the switch in the "on" position. What would cause that? It is a new Sierra coil.
Rich, if the contact points are closed, you may not see any voltage at the - side of the coil.

Thanks, Rich
 
Thanks Rick. I will check the position of the points. If closed, prop them open with folded paper and test the coil wire for voltage with the switch on. Assuming all is well with that, I guess I need to test the S circuit and the starter solenoid R or I terminals. If I need to, do you have a cheat sheet on testing those?
 
Thanks Rick. I will check the position of the points. If closed, prop them open with folded paper and test the coil wire for voltage with the switch on. Assuming all is well with that, I guess I need to test the S circuit and the starter solenoid R or I terminals. If I need to, do you have a cheat sheet on testing those?

You would want to disconnect the "Start-by-pass" wire from the ignition coil side of the ballast resistor.
As the starter motor is activated, you should see a voltage reading at this end of that wire, and no reading once the starter motor is disengaged.

 
You would want to disconnect the "Start-by-pass" wire from the ignition coil side of the ballast resistor.
As the starter motor is activated, you should see a voltage reading at this end of that wire, and no reading once the starter motor is disengaged.

Hi Rick, I disconnected the start-by-pass wire from the coil to check this. I got 8.9V and nor reading when disengaged. Should this voltage = the battery voltage or is there an issue? Thanks
 
yes, especially with no current flowing thru that wire...if the solenoid is OK, you will see the same voltage on the wire that is present at the battery terminal on the solenoid....

For what its worth, when diagnosing electrical issue using voltage measurements, its best to connect you meter to the "-" terminal of the battery for ALL measurements.....
 
Thanks, will try that again using the Batt terminal.

Other things:
For haha's I decided to test the continuity of the coil wire, removed it completely, lo and behold there was none. So that will be replaced. I did check the continuity on the black wire to the distributy from the -coil and that showed good. Tested the voltage between the - terminal of the coil & ground with switch "on" and got my 12.4 V. Did the same thing with the lead disconnected and got 12.4 V. The test routine I was following said that if the voltage rises to about 12 volts the distributy or the lead may be shorted to ground. Does that make any sense?
 
you didn't say if the points were opened or closed....with them being open, the 12.4 VDC makes sense, with the lead connected or not.

and by 'coil wire', if you mean the high voltage lead from the coil to the cap, there should be some resistance but not an open...so, maybe its time for a full ignition wire set...
 
you didn't say if the points were opened or closed....with them being open, the 12.4 VDC makes sense, with the lead connected or not.

and by 'coil wire', if you mean the high voltage lead from the coil to the cap, there should be some resistance but not an open...so, maybe its time for a full ignition wire set...
Hi- Sorry, I did have the points open, so that is good. And yes, it was the lead from the coil to the cap. Wires are 2 yrs old and probably less than 50 hours on them, surprised at that, as they were a quality set.
 
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Hi- Sorry, I did have the points open, so that is good.
And yes, it was the lead from the coil to the cap.
That would be your high tension cable.
Voltage at this point would be in the range of 35,000+ volts.

Wires are 2 yrs old and probably less than 50 hours on them, surprised at that, as they were a quality set.
Good quality spark plug cables should last for many years.
 
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Hi Rick, so would you say the high tension coil wire is good then? I tested it with a jumper to the battery (after I removed it) and to the test light and back to the battery, and nothing. Would it have that much resistance in it to prevent it from lighting? I did not try the test with the volt meter connected.
 
Turns out high tension wire is good. Resistance was a bit less than spec and voltage came thru perfect. Need to revisit the test in post #9, grounding to battery.
 
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