Voltage Drop when Cranking
Melting Slicks
Joined: Jun 2005
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From: Palatine, Peoples Republic of Illinois
St. Jude Donor '09-'10-'11-12-'13-'14-'15-'16-'17-‘18
NCM Sinkhole Donor
How did you wire up the distributor? If you used the original coil wire it won't work. The original drops the voltage during cranking.
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
As mentioned above, a battery voltage drop during cranking is normal. That's the reason there's the starter solenoid shunt wire to the coil to restore the correct amperage (not voltage) during cranking to the primary side of the ignition circuit in the stock points setup.
What source are you using to feed the BAT terminal of the HEI?
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From: New Or-leens Loo-z-anna
Are you checking for voltage drop AT THE BATT. TERMINAL OF THE DISTRIBUTOR CAP WHILE CRANKING THE ENGINE?
I ask because my distributor was showing 11 volts at BATT terminal with KEY ON...but getting only 6 volts intermittently AT the Batt. terminal while CRANKING....not nearly enough to produce a good spark.
Also....BLACK BUTTON is making good contact with bent metal tab on top of rotor?
I ask because my distributor was showing 11 volts at BATT terminal with KEY ON...but getting only 6 volts intermittently AT the Batt. terminal while CRANKING....not nearly enough to produce a good spark.
Also....BLACK BUTTON is making good contact with bent metal tab on top of rotor?
Thread Starter
Pro
Joined: Feb 2014
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From: Seguin TX
are you checking for voltage drop at the batt. Terminal of the distributor cap while cranking the engine?
i ask because my distributor was showing 11 volts at batt terminal with key on...but getting only 6 volts intermittently at the batt. Terminal while cranking....not nearly enough to produce a good spark.
measuring voltage at the coil power wires directly.
also....black button is making good contact with bent metal tab on top of rotor?carbon button in cap is making good contact with metal tab of rotor.
i ask because my distributor was showing 11 volts at batt terminal with key on...but getting only 6 volts intermittently at the batt. Terminal while cranking....not nearly enough to produce a good spark.
measuring voltage at the coil power wires directly.
also....black button is making good contact with bent metal tab on top of rotor?carbon button in cap is making good contact with metal tab of rotor.
Last edited by 68Thunder427; Mar 2, 2016 at 05:15 PM.
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From: Charlotte NC
Chances are that the terminal on the fuse panel goes DEAD when you try to CRANK the car. I have encountered this on some cars....worth checking out.
Keep in mind that the actual wire (12 gauge) that goes to an HEI actually comes DIRECTLY off the ignition switch that is mounted on top of your mast tube of your steering column.
AND...for what it is worth. Personally I do not like to connect an HEI power wire to the fuse panel...ESPECIALLY on the center terminal in the center of the fuse panel. The reason being.....the center terminals in a fuse panel is getting pwoer AFTER it passes THROUGH a fuse. SO...if there is any crossing or bad connecting a the fuse...you will be dealing with voltage drop due to a dirty/corroded fuse terminal holding in the fuse.
DUB
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From: Seguin TX
BUT....WHEN you go and turn the ignition key to START or CRANK...WHILE having your voltmeter AT THE FUSE PANEL where you connected the wire going to your BAT terminal on your HEI.....DO YOU STILL SHOW BATTERY VOLTAGE when you are turning the KEY????
Chances are that the terminal on the fuse panel goes DEAD when you try to CRANK the car. I have encountered this on some cars....worth checking out.
Keep in mind that the actual wire (12 gauge) that goes to an HEI actually comes DIRECTLY off the ignition switch that is mounted on top of your mast tube of your steering column.
AND...for what it is worth. Personally I do not like to connect an HEI power wire to the fuse panel...ESPECIALLY on the center terminal in the center of the fuse panel. The reason being.....the center terminals in a fuse panel is getting pwoer AFTER it passes THROUGH a fuse. SO...if there is any crossing or bad connecting a the fuse...you will be dealing with voltage drop due to a dirty/corroded fuse terminal holding in the fuse.
DUB
Chances are that the terminal on the fuse panel goes DEAD when you try to CRANK the car. I have encountered this on some cars....worth checking out.
Keep in mind that the actual wire (12 gauge) that goes to an HEI actually comes DIRECTLY off the ignition switch that is mounted on top of your mast tube of your steering column.
AND...for what it is worth. Personally I do not like to connect an HEI power wire to the fuse panel...ESPECIALLY on the center terminal in the center of the fuse panel. The reason being.....the center terminals in a fuse panel is getting pwoer AFTER it passes THROUGH a fuse. SO...if there is any crossing or bad connecting a the fuse...you will be dealing with voltage drop due to a dirty/corroded fuse terminal holding in the fuse.
DUB
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From: Charlotte NC
Have you checked the PICK UP COIL???
Also...not knowing if you have one or not....in the Corvette service manual that had HEI distributors there is section in the manual that gives you the tests to check the coil and pick up coil.
ALSO...not knowing if this matters or not....but I have run across new coils that are painted BLACK...and when installed....the paint effects the ground strap and wire that is needing to make contact with the outer metal housing of the coil.
If you have done all this and checked it out. I am at a loss on why you are not getting a spark....unless something crazy like you broke the cam gear and the distributor is not turning.
DUB
Also...not knowing if you have one or not....in the Corvette service manual that had HEI distributors there is section in the manual that gives you the tests to check the coil and pick up coil.
ALSO...not knowing if this matters or not....but I have run across new coils that are painted BLACK...and when installed....the paint effects the ground strap and wire that is needing to make contact with the outer metal housing of the coil.
If you have done all this and checked it out. I am at a loss on why you are not getting a spark....unless something crazy like you broke the cam gear and the distributor is not turning.
DUB
Thread Starter
Pro
Joined: Feb 2014
Posts: 692
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From: Seguin TX
[QUOTE=DUB;1591712193]Have you checked the PICK UP COIL???
Also...not knowing if you have one or not....in the Corvette service manual that had HEI distributors there is section in the manual that gives you the tests to check the coil and pick up coil.
ALSO...not knowing if this matters or not....but I have run across new coils that are painted BLACK...and when installed....the paint effects the ground strap and wire that is needing to make contact with the outer metal housing of the coil.
If you have done all this and checked it out. I am at a loss on why you are not getting a spark....unless something crazy like you broke the cam gear and the distributor is not turning.
DUB[/QUOTE
Just to clarify I replaced the original distributor with this new HEI about a year ago because the tach drive gear seized up on the original and going to get it rebuilt one these days LOL.
I just checked the pick up coil and I am getting 22 to 48 ohms as it spins around.
The cam gear is spinning the rotor.
Bottom side of coil is clean metal and making good contact with the metal strap. All wire connector are tight.
Going to pick up a new rotor and see if that could be the culprit maybe.
Also...not knowing if you have one or not....in the Corvette service manual that had HEI distributors there is section in the manual that gives you the tests to check the coil and pick up coil.
ALSO...not knowing if this matters or not....but I have run across new coils that are painted BLACK...and when installed....the paint effects the ground strap and wire that is needing to make contact with the outer metal housing of the coil.
If you have done all this and checked it out. I am at a loss on why you are not getting a spark....unless something crazy like you broke the cam gear and the distributor is not turning.
DUB[/QUOTE
Just to clarify I replaced the original distributor with this new HEI about a year ago because the tach drive gear seized up on the original and going to get it rebuilt one these days LOL.
I just checked the pick up coil and I am getting 22 to 48 ohms as it spins around.
The cam gear is spinning the rotor.
Bottom side of coil is clean metal and making good contact with the metal strap. All wire connector are tight.
Going to pick up a new rotor and see if that could be the culprit maybe.
Last edited by 68Thunder427; Mar 6, 2016 at 05:10 PM.
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Joined: Apr 2009
Posts: 19,294
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From: Charlotte NC
Just to clarify I replaced the original distributor with this new HEI about a year ago because the tach drive gear seized up on the original and going to get it rebuilt one these days LOL.
I just checked the pick up coil and I am getting 22 to 48 ohms as it spins around.
The cam gear is spinning the rotor.
Bottom side of coil is clean metal and making good contact with the metal strap. All wire connector are tight.
Going to pick up a new rotor and see if that could be the culprit maybe.
I just checked the pick up coil and I am getting 22 to 48 ohms as it spins around.
The cam gear is spinning the rotor.
Bottom side of coil is clean metal and making good contact with the metal strap. All wire connector are tight.
Going to pick up a new rotor and see if that could be the culprit maybe.
DUB
Last edited by DUB; Mar 6, 2016 at 05:17 PM.