Charging system failures
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Advanced
Joined: Sep 2020
Posts: 63
Likes: 6
Charging system failures
Is my new/rebuilt alternator suspect?
Car stalled, jumped started/drove home. Volt meter test across battery with engine running sub 12vdc.
Replaced alternator with rebuilt. Charge battery overnight. Parts store tested battery and new alternator. Alternator and battery passed test.
Headlights are now pulsing and random misfires popping up.
Did a voltage drop test from alternator frame to neg battery post engine running (54millivolt)
Unloaded engine running 13.8v at battery posts
Loaded engine running 13.3v at battery posts
Starts easy with no lag.
Battery is 5 years old but tests as good.
Why the pulsing lights and misfire?
Car stalled, jumped started/drove home. Volt meter test across battery with engine running sub 12vdc.
Replaced alternator with rebuilt. Charge battery overnight. Parts store tested battery and new alternator. Alternator and battery passed test.
Headlights are now pulsing and random misfires popping up.
Did a voltage drop test from alternator frame to neg battery post engine running (54millivolt)
Unloaded engine running 13.8v at battery posts
Loaded engine running 13.3v at battery posts
Starts easy with no lag.
Battery is 5 years old but tests as good.
Why the pulsing lights and misfire?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Sounds like your charging system is working OK. You are getting a LOW VOLTAGE at some where other than the charging circuit.
NOTE! You could be experiencing abnormal voltage input OR a shitty GROUND PATH.
Start with measuring the voltage on the circuit fuse for all of those individual circuits. On top of each fuse, are TWO TEST POINTS. Measure each test point to a proper ground. Look for full battery voltage on each fuse test point. I personally do a LOAD TEST with an incandescent lamp on each fuse while measuring circuit voltages. When you load down that fuse with a higher current device (test lamp), you should not see a significant voltage drop!
Another failure point is the B+ feed input for each fuse block. I personally remove the nut for the block, clean the terminals and properly tighten the nut for a proper connection. .
Your lights are on a hot at all times circuit. That would lead me to suspect a POOR GROUND PATH.
If it were ME, I would Inspect & clean ALL the under hood chassis grounds and ground blocks. I'm the person who likes to SEE THE SMOKING GUN that caused the issue. You can use a volt meter to read across the ground terminal to a very clean chassis point or battery ground terminal and see if you read ANY VOLTAGE DROP. The more voltage drop you see across a ground point the worst condition that ground point is in. Note, you may need to switch to the millivolt scale to measure some voltage drops. I would start in a scale that reads 0-20 VDC and then work to a lower scale..
When you turn your ignition switch to ON/RUN, it supplies power to all of the HOT IN ON/RUN powered devices. Those modules (PCM, BCM etc..) are powered by TWO power sources. ( HOT AT ALL TIMES & HOT IN ON & RUN) IN MY HONEST OPINION, I would load test and voltage test both the Hot in run and Hot at all times fuses.
Bill
NOTE! You could be experiencing abnormal voltage input OR a shitty GROUND PATH.
Start with measuring the voltage on the circuit fuse for all of those individual circuits. On top of each fuse, are TWO TEST POINTS. Measure each test point to a proper ground. Look for full battery voltage on each fuse test point. I personally do a LOAD TEST with an incandescent lamp on each fuse while measuring circuit voltages. When you load down that fuse with a higher current device (test lamp), you should not see a significant voltage drop!
Another failure point is the B+ feed input for each fuse block. I personally remove the nut for the block, clean the terminals and properly tighten the nut for a proper connection. .
Your lights are on a hot at all times circuit. That would lead me to suspect a POOR GROUND PATH.
If it were ME, I would Inspect & clean ALL the under hood chassis grounds and ground blocks. I'm the person who likes to SEE THE SMOKING GUN that caused the issue. You can use a volt meter to read across the ground terminal to a very clean chassis point or battery ground terminal and see if you read ANY VOLTAGE DROP. The more voltage drop you see across a ground point the worst condition that ground point is in. Note, you may need to switch to the millivolt scale to measure some voltage drops. I would start in a scale that reads 0-20 VDC and then work to a lower scale..
When you turn your ignition switch to ON/RUN, it supplies power to all of the HOT IN ON/RUN powered devices. Those modules (PCM, BCM etc..) are powered by TWO power sources. ( HOT AT ALL TIMES & HOT IN ON & RUN) IN MY HONEST OPINION, I would load test and voltage test both the Hot in run and Hot at all times fuses.
Bill
Last edited by Bill Curlee; Nov 26, 2023 at 04:10 PM.
Melting Slicks
Joined: Sep 2021
Posts: 2,555
Likes: 1,213
Read the sticky posts, the OEM alternators have something different about them that replacements often don't have. Bill probably knows what that is.
I'd try and get your original one back in case you end up needing to rebuild it instead of replace.
Thread Starter
Advanced
Joined: Sep 2020
Posts: 63
Likes: 6
Sounds like your charging system is working OK. You are getting a LOW VOLTAGE at some where other than the charging circuit.
NOTE! You could be experiencing abnormal voltage input OR a shitty GROUND PATH.
Start with measuring the voltage on the circuit fuse for all of those individual circuits. On top of each fuse, are TWO TEST POINTS. Measure each test point to a proper ground. Look for full battery voltage on each fuse test point. I personally do a LOAD TEST with an incandescent lamp on each fuse while measuring circuit voltages. When you load down that fuse with a higher current device (test lamp), you should not see a significant voltage drop!
Another failure point is the B+ feed input for each fuse block. I personally remove the nut for the block, clean the terminals and properly tighten the nut for a proper connection. .
Your lights are on a hot at all times circuit. That would lead me to suspect a POOR GROUND PATH.
If it were ME, I would Inspect & clean ALL the under hood chassis grounds and ground blocks. I'm the person who likes to SEE THE SMOKING GUN that caused the issue. You can use a volt meter to read across the ground terminal to a very clean chassis point or battery ground terminal and see if you read ANY VOLTAGE DROP. The more voltage drop you see across a ground point the worst condition that ground point is in. Note, you may need to switch to the millivolt scale to measure some voltage drops. I would start in a scale that reads 0-20 VDC and then work to a lower scale..
When you turn your ignition switch to ON/RUN, it supplies power to all of the HOT IN ON/RUN powered devices. Those modules (PCM, BCM etc..) are powered by TWO power sources. ( HOT AT ALL TIMES & HOT IN ON & RUN) IN MY HONEST OPINION, I would load test and voltage test both the Hot in run and Hot at all times fuses.
Bill
NOTE! You could be experiencing abnormal voltage input OR a shitty GROUND PATH.
Start with measuring the voltage on the circuit fuse for all of those individual circuits. On top of each fuse, are TWO TEST POINTS. Measure each test point to a proper ground. Look for full battery voltage on each fuse test point. I personally do a LOAD TEST with an incandescent lamp on each fuse while measuring circuit voltages. When you load down that fuse with a higher current device (test lamp), you should not see a significant voltage drop!
Another failure point is the B+ feed input for each fuse block. I personally remove the nut for the block, clean the terminals and properly tighten the nut for a proper connection. .
Your lights are on a hot at all times circuit. That would lead me to suspect a POOR GROUND PATH.
If it were ME, I would Inspect & clean ALL the under hood chassis grounds and ground blocks. I'm the person who likes to SEE THE SMOKING GUN that caused the issue. You can use a volt meter to read across the ground terminal to a very clean chassis point or battery ground terminal and see if you read ANY VOLTAGE DROP. The more voltage drop you see across a ground point the worst condition that ground point is in. Note, you may need to switch to the millivolt scale to measure some voltage drops. I would start in a scale that reads 0-20 VDC and then work to a lower scale..
When you turn your ignition switch to ON/RUN, it supplies power to all of the HOT IN ON/RUN powered devices. Those modules (PCM, BCM etc..) are powered by TWO power sources. ( HOT AT ALL TIMES & HOT IN ON & RUN) IN MY HONEST OPINION, I would load test and voltage test both the Hot in run and Hot at all times fuses.
Bill
With key on/engine on the headlights pulse until you bring the rpms up high.
Last edited by Travis Armstrong; Nov 26, 2023 at 04:56 PM. Reason: Typo
Drifting
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From: New Jersey
Moderator, Tech Contributor
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From: Cape Coral, Florida
Is my new/rebuilt alternator suspect?
Car stalled, jumped started/drove home. Volt meter test across battery with engine running sub 12vdc.
Replaced alternator with rebuilt. Charge battery overnight. Parts store tested battery and new alternator. Alternator and battery passed test.
Headlights are now pulsing and random misfires popping up.
Did a voltage drop test from alternator frame to neg battery post engine running (54millivolt)
Unloaded engine running 13.8v at battery posts
Loaded engine running 13.3v at battery posts
Starts easy with no lag.
Battery is 5 years old but tests as good.
Why the pulsing lights and misfire?
Car stalled, jumped started/drove home. Volt meter test across battery with engine running sub 12vdc.
Replaced alternator with rebuilt. Charge battery overnight. Parts store tested battery and new alternator. Alternator and battery passed test.
Headlights are now pulsing and random misfires popping up.
Did a voltage drop test from alternator frame to neg battery post engine running (54millivolt)
Unloaded engine running 13.8v at battery posts
Loaded engine running 13.3v at battery posts
Starts easy with no lag.
Battery is 5 years old but tests as good.
Why the pulsing lights and misfire?
With engine running at 2500 RPM and electrical load on it measure voltage drop from alternator B+ to battery positive...should not be more than 0.5 volts...normally around 0.2 to 0.3 volts....do the same from alternator case to battery negative...you can't do a voltage drop without current flow !!...i.e. engine off !!...pulsing lights are normally a ground issue.
Thread Starter
Advanced
Joined: Sep 2020
Posts: 63
Likes: 6
With engine running at 2500 RPM and electrical load on it measure voltage drop from alternator B+ to battery positive...should not be more than 0.5 volts...normally around 0.2 to 0.3 volts....do the same from alternator case to battery negative...you can't do a voltage drop without current flow !!...i.e. engine off !!...pulsing lights are normally a ground issue.
Back has been acting up and I've been slammed at work. Going to do more troubleshooting very soon.
