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Slow crank and huge voltage drop
#1
[font=.SF UI Display][font=.SFUIDisplay]—Hi guys. I’m having a heck of a time figuring this one out. Slow crank with huge voltage drop of 7-10 volts at positive side of the solenoid.[/font][/font]
[font=.SF UI Display][font=.SFUIDisplay]2 things I found. [/font][/font]
  1. [font=.SF UI Display][font=.SFUIDisplay]Remove 7mm coil wire from distributor and ground to manifold. Cranks fine no voltage drop. Put coil wire back on distributor and have voltage drop, slow cranking.[/font][/font]
  2. [font=.SF UI Display][font=.SFUIDisplay]Remove negative battery cable, positive cable still attached. Volt meter black probe to negative battery post and red probe to any bare metal. Volt meter reads 11.8 volts constant. Open the drivers door and volts now show 12.6. Press the door switch in and volts drop back to 11.8.[/font][/font]
[font=.SF UI Display][font=.SFUIDisplay]Same test on my other car with negative battery cable removed attach meter the same way and the voltage has a reading of say 9 volts but immediately starts to dissipitate the voltage slowly down to 0 volts. Which appears to be normal I think.[/font][/font]
[font=.SF UI Display][font=.SFUIDisplay]Any ideas would be appreciated. Engine was removed painted, engine box painted recently. Ran fine before this restoration done. Tried booster cables to test grounds from block to different places on firewall and around chassis but same issue prevails.[/font][/font]
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#2
Where is your negative battery cable connected? It should run from the battery to the bottom screw on the voltage regulator and from there to a bolt on the engine block. Scrape the paint off the block where the negative cable connects. Make sure all grounds and cable are clean. Pull the battery cables off the battery terminals and use a battery terminal wire brush on the posts and the insides of the terminal clamps.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
Battery post clean, negative bat cable runs from battery to front of engine block. Nothing goes to regulator just single cable bat to block.
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#4
The chassis also needs to be grounded, either directly from the battery, or from the block to the chassis.

Is the block clean where the cable connects to it? Paint is a good insulator.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#5
Here is the right ground cable. Several vendors sell them. The ground cable has 2 lugs.

here the link.
https://www.npdlink.com/store/products/m...-2869.html
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#6
Hi guys thanks for suggestions, so I’ve cleaned battery posts. Double checked and cleaned to bare metal. New negative cable to block. Added ground from clean metal of rear block to firewall. Added a third ground from neg bat post to inner fender below solenoid.  Same issue slow crank 7-10 volts being dropped.. Ran a fourth ground to be sure I’m grounded, from manifold to chassis. Same issue. Hard to read my original post so will reiterate the issue. Car turns over perfectly only when distributor side of coil 7mm wire is grounded to manifold. Also still have voltage when neg cable removed from bat. Test neg post to ground 11.8 volts (only poitive cable attached), open door and jumps to 12.6 volts. Car cranked well before with old spark plug wire set, but am sure they were arching because I remember getting a wicked shock when I touched one of the wires while setting the carb as engine was running. Once again any help is appreciated.
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#7
With negative battery cable disconnected, you should not see any voltage from battery negative post to chassis or engine ground. If you do, that says something in the chassis/engine/alternator is connected directly to the battery. Try disconnecting the voltage regulator first, then the alternator lines, and seeing if the system improves.

Let me check your shorts!
http://midlifeharness.com

[Image: Flamicon2.jpg]


[Image: oldfart.png]
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#8
Thanks for suggestion. Disconnected voltage regulator, then removed wires off alternator. Also removed coil + and - wires. No change still shows voltage. But I did find the coil is leaking oil.
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#9
Try disconnecting the + wire from your coil, and then measure the negative terminal to ground voltage. Try cranking the engine with the + coil wire disconnected.

You definitely have something drawing voltage, a short, or something that is staying on. When you open the door the voltage reading goes up because it turns the dome light on, which is more of a draw than the short or other voltage draw.

Try disconnecting the starter side of the solenoid and the measure the negative terminal to ground voltage.

You'll have to systematically go through circuits until you find the one that is drawing current when it shouldn't. You can also disconnect the fuses one at a time. When you find the bad circuit you'll have to trace it and disconnect and/or replace whatever component it is connected to.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#10
Can you post a pic of the wiring at the solenoid?

'73 Grandé H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

'73 F code convertible. Bright red. Needs total restore. (IE HOT MESS)

- Jason
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