Using a multimeter to troubleshoot charging
11-07-2010, 12:45 PM
#1
Using a multimeter to troubleshoot charging My check gauges light cam eon yesterday afternoon and my battery is dying.
I drove the car to Pep Boys today because it was the closest shop for a quick diagnosis and I didn't want to unnecessarily drain te battery by drivinf further. The guy who worked on it said he owned a 2000 Camaro and we chatted a bit about my LS3 motor and about local car meetings. Their test said it was a bad alternator, then I asked if they ruled out the wiring, and they said they'd get back to me. They called me back awhile later to say that due to the various shrink-wrapped patches made by the dealer a few years ago, they aren't going to try to diagnose it and sent me home without charging me anything.
Unless I can find something in the driveway, I'll probably drive it a mile up the road to the dealer tomorrow. I've found these tips in other topics... anything else?
1. Pull the battery ground off. If the alternator is bad, the car will die. If it's good, the car will continue to run
2. Check voltage on the battery (red meter wire to positive and black to negative). Start the car and check the voltage at the battery the same way. With the car running you should be about 13.5-14vdc. If this is true then the alternator, belt, wires and voltage regulator are good. If something is wrong with this step try checking voltage right at the alternator wires. If its good here then you need to look at the wires between the alternator and battery.
3. Make sure the engine is grounded really good. Set your meter to "ohms" and put one meter wire an unpainted part of the engine and the other lead on the negative battery post. You should have something close to "0"
4. Check the voltage at the alternator output and compare it to the battery + (neg probe should be at battery - for both checks). If there is more than a fraction of a volt difference, you have bad continuity somewhere. If voltages are close, your charging system is weak.
In #4, where do I place the leads to check the alternator output?
I drove the car to Pep Boys today because it was the closest shop for a quick diagnosis and I didn't want to unnecessarily drain te battery by drivinf further. The guy who worked on it said he owned a 2000 Camaro and we chatted a bit about my LS3 motor and about local car meetings. Their test said it was a bad alternator, then I asked if they ruled out the wiring, and they said they'd get back to me. They called me back awhile later to say that due to the various shrink-wrapped patches made by the dealer a few years ago, they aren't going to try to diagnose it and sent me home without charging me anything.
Unless I can find something in the driveway, I'll probably drive it a mile up the road to the dealer tomorrow. I've found these tips in other topics... anything else?
1. Pull the battery ground off. If the alternator is bad, the car will die. If it's good, the car will continue to run
2. Check voltage on the battery (red meter wire to positive and black to negative). Start the car and check the voltage at the battery the same way. With the car running you should be about 13.5-14vdc. If this is true then the alternator, belt, wires and voltage regulator are good. If something is wrong with this step try checking voltage right at the alternator wires. If its good here then you need to look at the wires between the alternator and battery.
3. Make sure the engine is grounded really good. Set your meter to "ohms" and put one meter wire an unpainted part of the engine and the other lead on the negative battery post. You should have something close to "0"
4. Check the voltage at the alternator output and compare it to the battery + (neg probe should be at battery - for both checks). If there is more than a fraction of a volt difference, you have bad continuity somewhere. If voltages are close, your charging system is weak.
In #4, where do I place the leads to check the alternator output?
11-07-2010, 02:40 PM
#2
1. Can't try at this time because I forgot my socket set at a friends house yesterday.
2. Motor off: 11.59V, idle 11.37V, add headlights 11.21V, add heater 11.17V.
3. Engine off - PS head: 4.1 ohms, DS head 4.1 ohms, water pump 4.1 ohms, EGR blockoff plate 4.9 ohms, fuel rail 4.9 ohms. Erm, is that considered 'close' to zero? Or does this need to be done with motor running?
4. Haven't tried, may be difficult with my probe-style leads instead of alligator leads.
2. Motor off: 11.59V, idle 11.37V, add headlights 11.21V, add heater 11.17V.
3. Engine off - PS head: 4.1 ohms, DS head 4.1 ohms, water pump 4.1 ohms, EGR blockoff plate 4.9 ohms, fuel rail 4.9 ohms. Erm, is that considered 'close' to zero? Or does this need to be done with motor running?
4. Haven't tried, may be difficult with my probe-style leads instead of alligator leads.
Last edited by JimMueller; 11-07-2010 at 02:46 PM.
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11-08-2010, 08:40 AM
#10
Only one vehicle and alternator is under warranty. Was at 11V key on this morning, 10.5V at colt start, and dropped to 8.3V by the time I arrived at the dealer. Said they'd warranty the alternator but not the labor because another dealer did the work.
11-08-2010, 08:54 AM
#11
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There is a PCM connection that messes with the alternator.
Never had a call to look into it or understand why.
I'd start with looking at the battery terminal voltage, the
center screws - need to see the full charging voltage at
idle.
Then battery center terminal to engine block and to the
sheet meal - I'd want <100mV solid. Try again w/ A/C and
headlights on.
Then get under it and see if the alt output to case, is the
same value as at the battery posts. That will pretty much
tell you about wiring / ground issues.
The "L terminal" deal, you're on your own....
Never had a call to look into it or understand why.
I'd start with looking at the battery terminal voltage, the
center screws - need to see the full charging voltage at
idle.
Then battery center terminal to engine block and to the
sheet meal - I'd want <100mV solid. Try again w/ A/C and
headlights on.
Then get under it and see if the alt output to case, is the
same value as at the battery posts. That will pretty much
tell you about wiring / ground issues.
The "L terminal" deal, you're on your own....
11-08-2010, 01:51 PM
#14
The advisor first came back to ask me if I race the car, although that shouldn't effect the alternator, right? I told him not since last November, but I forgot about LSFest. But that was a few months ago. Anyway, they replaced the alternator under warranty and I paid one hour labor. The tech advised the voltage was dropping in the upper RPM's with the replacement alternator, so he thought a more robust alternator might be worthwhile?
Off the top of my head, the only electrical modifications I have are:
- Walbro hotwire kit
- Passenger window motor kit
- Hardwired Valentine 1 power kit, although I haven't had the V1 in the car for years.
- Wire for electric cut-out switch, but removed the actual motor and left the wiring installed years ago.
A friend indicated the stock vehicle has some sort of shield on the alternator to deflect fluid intrusion, is that correct? I don't recall seeing one on the replacement alternators I've gone through. There are one, maybe two plastic shrouds that were originally near near the radiator which I removed many years ago. I'd really like to stop going through alternators at least once a year for the last 3 years.
Off the top of my head, the only electrical modifications I have are:
- Walbro hotwire kit
- Passenger window motor kit
- Hardwired Valentine 1 power kit, although I haven't had the V1 in the car for years.
- Wire for electric cut-out switch, but removed the actual motor and left the wiring installed years ago.
A friend indicated the stock vehicle has some sort of shield on the alternator to deflect fluid intrusion, is that correct? I don't recall seeing one on the replacement alternators I've gone through. There are one, maybe two plastic shrouds that were originally near near the radiator which I removed many years ago. I'd really like to stop going through alternators at least once a year for the last 3 years.
