voltage drop
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Instructor
Joined: Oct 2007
Posts: 124
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From: baltimore ohio
voltage drop
Hey I thought I would throw this out their. Installed new cam this winter, Know when I try to start the car battery voltage drop from high 13's to below 9. Let go of the key and voltage goes back to high 13's, Had battery checked at 2 places, it good, installed new positive and ground cables, and new starter. Also check power at hei its high 13's then hit the key and it drops. Disconnected the alternator no change. Also checked ground at engine it is good. If I have the distributor in wrong could that be pulling to much power? What do you think? 
Race Director
Joined: Jul 2015
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From: SW Florida.
Is the motor cranking? Has it been sitting a long time? New cam. Break in additive in there? You should pre-oil it. I use an old distributor. A long screwdriver blade chucked in a drill will do in a pinch. Mebbe even pull intake and pour the additive right on the cam
Last edited by derekderek; May 27, 2018 at 11:55 AM.
Race Director
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From: Virginia
Can you clarify?
13.7 VDC when car is sitting there? Is there a battery charger attached? That's high for a battery by itself.
Below 9 VDC when you "start" the car. What do you mean? Is the ignition in "ON" position, or in "Start" position? With the starter cranking, 9 VDC could be fine, as long as it turns over.
Where/how are you measuring these voltages? Does the starter turn the engine over, but not fire?
What is the voltage of the battery (measured at the battery) with everything off, and the headlights on? Headlighs off? Please use a multimeter, not the voltmeter in your dash. That should be a draw comparable to your ignition system (not the starter), so depending on if you get the massive voltage drop or not, either your battery is dead, or something else is going on.
Most of my weird electrical issues have been tied to a bad batttery, or bad electrical connection, usually at the battery, but perhaps at the starter.
13.7 VDC when car is sitting there? Is there a battery charger attached? That's high for a battery by itself.
Below 9 VDC when you "start" the car. What do you mean? Is the ignition in "ON" position, or in "Start" position? With the starter cranking, 9 VDC could be fine, as long as it turns over.
Where/how are you measuring these voltages? Does the starter turn the engine over, but not fire?
What is the voltage of the battery (measured at the battery) with everything off, and the headlights on? Headlighs off? Please use a multimeter, not the voltmeter in your dash. That should be a draw comparable to your ignition system (not the starter), so depending on if you get the massive voltage drop or not, either your battery is dead, or something else is going on.
Most of my weird electrical issues have been tied to a bad batttery, or bad electrical connection, usually at the battery, but perhaps at the starter.
Instructor
Joined: Sep 2017
Posts: 169
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From: Westlake Ohio
Industry battery load test spec standard used to be to 1/2 ccw load and maintain for 15 seconds battery should never drop below 9.6 volts. If you are cranking and battery drops below 9v you prolly need a battery IMO
Burning Brakes
Joined: Jan 2012
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Did this condition just start with the cam install? Before the cam install, did the engine crank and start normally? Is it the same battery?
A simple voltage drop test on the battery cables would be where I would start.
A simple voltage drop test on the battery cables would be where I would start.
Thread Starter
Instructor
Joined: Oct 2007
Posts: 124
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From: baltimore ohio
hey thanks for your thoughts, found bad coil that's the second one in less than a year, and I was 180 out still working on it, Will update
Race Director
Joined: Sep 2004
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
that's the range of normal...maybe a little on the low side.
that's why we have ballast resistors in some cars since the cranking voltage drops down to 9.6 volts.
that's why we have ballast resistors in some cars since the cranking voltage drops down to 9.6 volts.
