Question on voltage - start vs run
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Joined: May 2017
Posts: 63
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From: Memphis TN
Question on voltage - start vs run
I have a 1969 L46 350 with a 4 spd. I bought the car in non-running condition and trying to get it back on the road. I have the original points distributor and would like to upgrade to HEI. I bought an HEI distributor from Skip White Performance (https://www.skipwhiteperformance.com...6515-bk_83450/). I ran a new wire from the IGN terminal on the fuse box to the BAT terminal on the distributor. I disconnected the wire from the starter. I taped up the wire that was on the coil side. I removed the old coil and the ballast resistor. The problem is I have very weak spark. With the ignition switch in the RUN position, I have 12 volts at the BAT terminal. When in the START position with the starter engaged, it drops to 9.5-10 volts, which I believe is not enough for the HEI. This is across the entire system. Even taking a measurement at the alternator, it drops to 9.5-10 volts. What am I missing? How do I get 12 volts to the HEI when the starter is engaged? Perhaps the starter has a short in it?
Thanks,
David
Thanks,
David
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.
I have a 1969 L46 350 with a 4 spd. I bought the car in non-running condition and trying to get it back on the road. I have the original points distributor and would like to upgrade to HEI. I bought an HEI distributor from Skip White Performance (https://www.skipwhiteperformance.com...6515-bk_83450/). I ran a new wire from the IGN terminal on the fuse box to the BAT terminal on the distributor. I disconnected the wire from the starter. I taped up the wire that was on the coil side. I removed the old coil and the ballast resistor. The problem is I have very weak spark. With the ignition switch in the RUN position, I have 12 volts at the BAT terminal. When in the START position with the starter engaged, it drops to 9.5-10 volts, which I believe is not enough for the HEI. This is across the entire system. Even taking a measurement at the alternator, it drops to 9.5-10 volts. What am I missing? How do I get 12 volts to the HEI when the starter is engaged? Perhaps the starter has a short in it?
Thanks,
David
Thanks,
David
1) How do you know your spark is "very weak"?
2) What size/age is your battery? Cranking an engine is naturally going to drop the battery/system voltage due to all the current being drawn by the starter.
3) A genuine HEI is designed to operate down to 6 volts (I have no idea what the Chinese ripoffs work down to.). The spark output should still be fine during cranking at 9.5-10 volts.
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Joined: May 2017
Posts: 63
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From: Memphis TN
A few items:
1) How do you know your spark is "very weak"?
I pulled #1 cylinder spark plug and let it rest on a ground. I watched the plug as someone else cranked the engine. I also tried a Lisle induction spark tester, but it showed no spark.
2) What size/age is your battery? Cranking an engine is naturally going to drop the battery/system voltage due to all the current being drawn by the starter.
New Interstate battery from Costco in November. I still have the original battery cables. Do battery cables go bad?
3) A genuine HEI is designed to operate down to 6 volts (I have no idea what the Chinese ripoffs work down to.). The spark output should still be fine during cranking at 9.5-10 volts.
1) How do you know your spark is "very weak"?
I pulled #1 cylinder spark plug and let it rest on a ground. I watched the plug as someone else cranked the engine. I also tried a Lisle induction spark tester, but it showed no spark.
2) What size/age is your battery? Cranking an engine is naturally going to drop the battery/system voltage due to all the current being drawn by the starter.
New Interstate battery from Costco in November. I still have the original battery cables. Do battery cables go bad?
3) A genuine HEI is designed to operate down to 6 volts (I have no idea what the Chinese ripoffs work down to.). The spark output should still be fine during cranking at 9.5-10 volts.
Instructor
Joined: May 2017
Posts: 100
Likes: 5
From: I don't do cities N/W Montana & Nor California
I have recently had to tackle this when I installed my New MSD system on my new rebuilt motor.
I don't know all the technicals but my old positive coil wire that produces 12 volts when the key is on is powering my MSD system fine at this point. I don't know if the voltage drops since it starts in my motor fine I haven't bothered to get into that.
I don't know all the technicals but my old positive coil wire that produces 12 volts when the key is on is powering my MSD system fine at this point. I don't know if the voltage drops since it starts in my motor fine I haven't bothered to get into that.
Racer
Joined: Aug 2013
Posts: 339
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From: Fayetteville NC
I just installed a new Hei/Msd distributer after running one that came with the stroker motor. I have no issues. I agree with 69427. How old is your battery/size? What are the readings while the motor is running on the alternator verse the start reading from the battery?
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Joined: May 2017
Posts: 63
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From: Memphis TN
I just installed a new Hei/Msd distributer after running one that came with the stroker motor. I have no issues. I agree with 69427.
How old is your battery/size?
What are the readings while the motor is running on the alternator verse the start reading from the battery?
How old is your battery/size?
What are the readings while the motor is running on the alternator verse the start reading from the battery?
What are the readings while the motor is running on the alternator verse the start reading from the battery?
I haven't been able to start the engine yet.
Racer
Joined: Aug 2013
Posts: 339
Likes: 54
From: Fayetteville NC
During start, you should have 12v and will drop during start. Once the motor is running, you should have at least 13v to your battery which means your alternator is recharging your battery.
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Team Owner
Joined: Mar 2002
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From: Huntsville AL
Understand you have a HEI but;
On a 69 with stock unmolested wiring you will have less than 12V in the run position and 12V (or what the Batt is holding) in the start position.
Also you have two wires going to the coil 1) run voltage & 2) start voltage both are powered independently via the ignition switch.
On a 69 with stock unmolested wiring you will have less than 12V in the run position and 12V (or what the Batt is holding) in the start position.
Also you have two wires going to the coil 1) run voltage & 2) start voltage both are powered independently via the ignition switch.
Burning Brakes
Joined: Sep 2016
Posts: 927
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From: Dutchess county New York
Understand you have a HEI but;
On a 69 with stock unmolested wiring you will have less than 12V in the run position and 12V (or what the Batt is holding) in the start position.
Also you have two wires going to the coil 1) run voltage & 2) start voltage both are powered independently via the ignition switch.
On a 69 with stock unmolested wiring you will have less than 12V in the run position and 12V (or what the Batt is holding) in the start position.
Also you have two wires going to the coil 1) run voltage & 2) start voltage both are powered independently via the ignition switch.
Last edited by pigfarmer; Feb 12, 2018 at 12:55 PM.