Coil voltage drops from 10 to 6 when cranking

[bounce]

240z 71

is that really bad ? or normal?

is it an ignition switch contact?

[Shade133]

i think everyone will need a bit more info. like what do you mean by cranking? as in starting? maybe your battery is low, or more like your alt isnt producing enough power at crank

Edited July 14, 2010 by Shade133

[bounce]

k, I'm not getting spark out of the coil to the distributor....

I have a new battery.

a volt meter plugged into the two terminals that attach to the coil gives me a reading of 10 volts with key On, and drops to 6 volts whilst cranking/ starting....

if I'm getting that voltage in to the coil...and nothing is coming out when testing for spark with the coil to distributor wire..(looking for arc on chasis/body)...could it be the ignition coil?

[Shade133]

ya sounds like the coil is bad

[EScanlon]

Check the wiring at the Ignition Switch, especially if it's been cobbled by an IPO.

The voltage swap you're mentioning happens with the 240 Ignition Systems to lower the voltage on the points while running and reducing the chance of burning them.

2¢

E

[sblake01]

Are we simply talking about the function of the ballast resistor?

[EScanlon]

Yes, except that what he mentions is inverted. i.e. His voltage DROPS when the starter is engaged and RAISES on "RUN".

That's the OPPOSITE of what should be happening normally, as you know.

E

[Mikes Z car]

Hmm I wonder if the points opening and closing could make it appear the voltage dropped because with the points in action there wouldn't be a continuous DC on the coil as there might be when measuring with the engine not running?

Mike

[zKars]

Check the voltage between the + coil terminal and a nearby metal ground point. Do not use the coil - as a reference. Do the crank verses run comparison and let us know.

Run a wire from the + terminal on the battery directly to the + side of the coil and see if you get spark when cranking or if it starts. This will by pass the ign switch.

[SteveJ]

Hmm I wonder if the points opening and closing could make it appear the voltage dropped because with the points in action there wouldn't be a continuous DC on the coil as there might be when measuring with the engine not running?

Mike

That would be ridiculously easy to check with an oscilloscope. I have one that uses a computer for the display. It was less than $200. However, I don't have points in my 73. I got rid of them about 12 years ago.