71 Coil Voltage
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Pro
Joined: Nov 2008
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From: Denham Springs LA
71 Coil Voltage
As long as I am in neutral the car revs great. When Sunday driving around town the car runs, idles in gear, and slowly accelerates fine. But when I accelerate more than normal driving the engine starts missing. Car is all stock with 58K miles. New coil, points, condensor, spark plugs, and spark plug wires. Car ran the same with old components.
I have narrowed the problem down to coil voltage.
With the key on, engine off, voltage at coil + terminal is 12 volts.
With engine running, voltage at coil + terminal is 9 volts.
I ran a new wire from the altenator + post, through a mallory 1.2 ohm resistor, to the + post on coil and car runs great under light and heavy acceleration. With this setup engine running, voltage at coil + terminal is 10volts. However I can't turn the engine off without raising the hood and disconnecting the wire.
So I ran a new wire from the fuse panel to mallory 1.2 ohm resistor, to the + post on coil and engine is missing again during heavy acceleration.
What's going on here?
Roger
I have narrowed the problem down to coil voltage.
With the key on, engine off, voltage at coil + terminal is 12 volts.
With engine running, voltage at coil + terminal is 9 volts.
I ran a new wire from the altenator + post, through a mallory 1.2 ohm resistor, to the + post on coil and car runs great under light and heavy acceleration. With this setup engine running, voltage at coil + terminal is 10volts. However I can't turn the engine off without raising the hood and disconnecting the wire.
So I ran a new wire from the fuse panel to mallory 1.2 ohm resistor, to the + post on coil and engine is missing again during heavy acceleration.
What's going on here?
Roger
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Before changing the coil...
Do you know if the dwell is steady from idle through a few thousand RPM?
With the vacuum advance can disconnected and plugged does the timing advance as RPM increases?
If your using full manifold vacuum does the timing advance when you connect the vacuum advance?
Not sure which wire your talking about.
With the vacuum advance can disconnected and plugged does the timing advance as RPM increases?
If your using full manifold vacuum does the timing advance when you connect the vacuum advance?
Not sure which wire your talking about.
Thread Starter
Pro
Joined: Nov 2008
Posts: 680
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From: Denham Springs LA
I have the dwell set at 30. It remains constant from idle to at least 1500rpm. I haven't checked it at any higher RPM.
Yes my timing advances with the vacuum advance disconnected and plugged. I took the distributor apart and cleaned it up. Everything seemed to be in good shape. I shimmed the drive gear to get the correct clearance.
My car has the solenoid that doesn't allow vacuum to the distributor unless it's in 3rd gear, or heavy traffic and the engine temp is a little higher, and a couple of other conditions, but most of the time it doesn't allow vacuum to the distributor. I have ran it both ways (with and without and it doesn't make a difference.
I don't see the tan wire shown on the wiring diagram in my AIM.
Yes my timing advances with the vacuum advance disconnected and plugged. I took the distributor apart and cleaned it up. Everything seemed to be in good shape. I shimmed the drive gear to get the correct clearance.
My car has the solenoid that doesn't allow vacuum to the distributor unless it's in 3rd gear, or heavy traffic and the engine temp is a little higher, and a couple of other conditions, but most of the time it doesn't allow vacuum to the distributor. I have ran it both ways (with and without and it doesn't make a difference.
I don't see the tan wire shown on the wiring diagram in my AIM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
OK. I can't see your car so I can only give you info and suggestions. The '71 had a resistance wire running from the fuse block on the firewall to the positive terminal on the coil. There is also another [yellow, I think] wire on that terminal which comes from the starter solenoid via the wiring harness. The resistance wire should provide all the resistance you need for the coil; adding another resistor into the line is severely reducing the current to supply the coil.
Also, that coil needs to be correct for a vehicle with an "internal resistance"...meaning a car with a ballast resistor or with a resistance wire in the circuit. So, the coil must match with the system you have. If you have a standard [12 volt supply] coil on the car, the windings are not the same as the one designed for your car.
Correct those issues and see how it goes.
Also, that coil needs to be correct for a vehicle with an "internal resistance"...meaning a car with a ballast resistor or with a resistance wire in the circuit. So, the coil must match with the system you have. If you have a standard [12 volt supply] coil on the car, the windings are not the same as the one designed for your car.
Correct those issues and see how it goes.
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Joined: Oct 2000
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From: Santa Ana CA
As long as I am in neutral the car revs great. When Sunday driving around town the car runs, idles in gear, and slowly accelerates fine. But when I accelerate more than normal driving the engine starts missing. Car is all stock with 58K miles. New coil, points, condensor, spark plugs, and spark plug wires. Car ran the same with old components.
I have narrowed the problem down to coil voltage.
With the key on, engine off, voltage at coil + terminal is 12 volts.
With engine running, voltage at coil + terminal is 9 volts.
I ran a new wire from the altenator + post, through a mallory 1.2 ohm resistor, to the + post on coil and car runs great under light and heavy acceleration. With this setup engine running, voltage at coil + terminal is 10volts. However I can't turn the engine off without raising the hood and disconnecting the wire.
So I ran a new wire from the fuse panel to mallory 1.2 ohm resistor, to the + post on coil and engine is missing again during heavy acceleration.
What's going on here?
Roger
I have narrowed the problem down to coil voltage.
With the key on, engine off, voltage at coil + terminal is 12 volts.
With engine running, voltage at coil + terminal is 9 volts.
I ran a new wire from the altenator + post, through a mallory 1.2 ohm resistor, to the + post on coil and car runs great under light and heavy acceleration. With this setup engine running, voltage at coil + terminal is 10volts. However I can't turn the engine off without raising the hood and disconnecting the wire.
So I ran a new wire from the fuse panel to mallory 1.2 ohm resistor, to the + post on coil and engine is missing again during heavy acceleration.
What's going on here?
Roger
My Mallory box was missing under load until I cleaned the fuse. The unit worked fine after that.
Thread Starter
Pro
Joined: Nov 2008
Posts: 680
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From: Denham Springs LA
7T1Vette,
I checked the resistance between the fuse panel and the coil for the resistance wire and get 1.4 ohms so I believe it's okay. The new coil and all parts are Delco stock parts. When I run a new wire with the Mallory resistor I have the original resistance wire disconnected. My dilema is that I am not getting enough current to the fuse panel, I think.
Where does the power at the fuse panel come from? I have an aim manual with a wiring diagram but I don't know if it's right. It doesn't match the wiring colors that my wiring harness for the coil is. It also shows the 12v wire going to the negative post on the coil.
Running a new wire with a resistor from the altenator to the coil makes my car run great.
Running a new wire with a resistor from the fuse panel doesn't fix my problem. I have the wire connected to the same circuit that feeds the resistance wire so I suspect the power source to the fuse panel/coil resistance wire is my issue.
Toddalin,
I will clean my fuse terminals and see if that helps. Thanks for the tip.
I checked the resistance between the fuse panel and the coil for the resistance wire and get 1.4 ohms so I believe it's okay. The new coil and all parts are Delco stock parts. When I run a new wire with the Mallory resistor I have the original resistance wire disconnected. My dilema is that I am not getting enough current to the fuse panel, I think.
Where does the power at the fuse panel come from? I have an aim manual with a wiring diagram but I don't know if it's right. It doesn't match the wiring colors that my wiring harness for the coil is. It also shows the 12v wire going to the negative post on the coil.
Running a new wire with a resistor from the altenator to the coil makes my car run great.
Running a new wire with a resistor from the fuse panel doesn't fix my problem. I have the wire connected to the same circuit that feeds the resistance wire so I suspect the power source to the fuse panel/coil resistance wire is my issue.
Toddalin,
I will clean my fuse terminals and see if that helps. Thanks for the tip.
Thread Starter
Pro
Joined: Nov 2008
Posts: 680
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From: Denham Springs LA
Last night I started checking voltage at various locations. Found wiring near starter very close to exhaust manifold and kinked with tie wrap. Removed tie wrap and straightened wiring. Moved wiring away from exhaust manifold.
Found wire connector on TCS relay on firewall not all the way connected.
Checked voltages in rats nest of wires on drivers side of engine compartment with large red wires. Found online fuse holder pretty dirty. Cleaned it up.
Now its running great - no missing. Wish I knew what fixed it. I suspect the problem wil reappear but for now it sure is nice to hear it running smooth.
Found wire connector on TCS relay on firewall not all the way connected.
Checked voltages in rats nest of wires on drivers side of engine compartment with large red wires. Found online fuse holder pretty dirty. Cleaned it up.
Now its running great - no missing. Wish I knew what fixed it. I suspect the problem wil reappear but for now it sure is nice to hear it running smooth.
Last edited by roger3; Apr 8, 2010 at 09:27 AM.
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Melting Slicks
Joined: Sep 2005
Posts: 2,720
Likes: 904
From: Warminster PA
Last night I started checking voltage at various locations. Found wiring near starter very close to exhaust manifold and kinked with tie wrap. Removed tie wrap and straightened wiring. Moved wiring away from exhaust manifold.
Found wire connector on TCS relay on firewall not all the way connected.
Checked voltages in rats nest of wires on drivers side of engine compartment with large red wires. Found online fuse holder pretty dirty. Cleaned it up.
Now its running great - no missing. Wish I knew what fixed it. I suspect the problem wil reappear but for now it sure is nice to hear it running smooth.
Found wire connector on TCS relay on firewall not all the way connected.
Checked voltages in rats nest of wires on drivers side of engine compartment with large red wires. Found online fuse holder pretty dirty. Cleaned it up.
Now its running great - no missing. Wish I knew what fixed it. I suspect the problem wil reappear but for now it sure is nice to hear it running smooth.
Glad to hear you are back up and running.
Tom
Thread Starter
Pro
Joined: Nov 2008
Posts: 680
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From: Denham Springs LA
Tom,
Thanks. I've had the car for about 5 months and finally getting to enjoy driving it. Just in time for the beautiful weather.
What is this group of wires for? They connect to some sort of relay but they sure are routed ugly.
Roger
Thanks. I've had the car for about 5 months and finally getting to enjoy driving it. Just in time for the beautiful weather.
What is this group of wires for? They connect to some sort of relay but they sure are routed ugly.
Roger
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
roger3... You have identified one of the glaring errors in the 1971 Corvette electrical diagram--the reversal of the polarity signs on the coil. If you check other year's diagrams, they are correct; only the '71 has it 'backwards'. And, they have the same diagram in the Chassis Service Manual.
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
That area is a distribution box, the red wire with the white on it should be the inline fuse for the high speed heater/Ac blower motor.
Melting Slicks
Joined: Sep 2005
Posts: 2,720
Likes: 904
From: Warminster PA
That is the horn relay. Your wiring diagram will show you where all of those wires go. The one looks like an inline fuse which is not factory installed so someone added that.
This is a shot from my car. Probably not much help since the power brake booster puts the master cylinder in the way.
Tom
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
The tan going to the coil is fed by the 12 pink. The pink comes from the ignition switch and is fed by the 12 brown.
You might have a problem where the tan and the pink meet in the bulkhead connector.
As thoyer said inside the yellow circle is the horn relay and power junction. There is also several fusible links in that mess of wires.
The inline fuse holder should be the high speed heater blower fuse.
You might have a problem where the tan and the pink meet in the bulkhead connector.
As thoyer said inside the yellow circle is the horn relay and power junction. There is also several fusible links in that mess of wires.
The inline fuse holder should be the high speed heater blower fuse.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
That is a very good question. And I have assumed that the high-speed blower fuse was built into the main electrical harness for all C3's. However, after searching through the '71 AIM, I found a small "note" on page #335 [UPC C60; sheet E4] which states "FUSE HOLDER & FUSE (part of A/C harn. asm.)". So, there is apparently a different harness used for the A/C cars which has that 30 amp fuse holder built in to it. No fuse holder/fuse in the non-A/C cars!
Since A/C and non-A/C cars have a high-speed on the blower switch, I can only assume that the A/C version draws more current through that hi-speed line...maybe because cold air is heavier than ambient air, thus the [same] blower does more work.
Since A/C and non-A/C cars have a high-speed on the blower switch, I can only assume that the A/C version draws more current through that hi-speed line...maybe because cold air is heavier than ambient air, thus the [same] blower does more work.
Last edited by 7T1vette; Apr 9, 2010 at 10:48 AM.
Melting Slicks
Joined: Sep 2005
Posts: 2,720
Likes: 904
From: Warminster PA
That is a very good question. And I have assumed that the high-speed blower fuse was built into the main electrical harness for all C3's. However, after searching through the '71 AIM, I found a small "note" on page #335 [UPC C60; sheet E4] which states "FUSE HOLDER & FUSE (part of A/C harn. asm.)". So, there is apparently a different harness used for the A/C cars which has that 30 amp fuse holder built in to it. No fuse holder/fuse in the non-A/C cars!
Since A/C and non-A/C cars have a high-speed on the blower switch, I can only assume that the A/C version draws more current through that hi-speed line...maybe because cold air is heavier than ambient air, thus the [same] blower does more work.
Since A/C and non-A/C cars have a high-speed on the blower switch, I can only assume that the A/C version draws more current through that hi-speed line...maybe because cold air is heavier than ambient air, thus the [same] blower does more work.
Tom
Le Mans Master
Joined: Aug 2006
Posts: 7,431
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
By 74 GM must have thought it was to easy to get to the horn relay so they moved mine to under the dash and above the speedometer!!!
I just have a junction box in that area and no indication of where the inline fuse is located, I just found it by chance.
I just have a junction box in that area and no indication of where the inline fuse is located, I just found it by chance.
