Power Problem
05-24-2010, 10:46 AM
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Power Problem Im having a bit if a power issue and need some help. After i start my car up i read around 14 volts sitting in park. When i place it in drive or any other gear i drop down to around 10-11 volts then when i start accelerating it goes back up to 14 volts. I have had the alternator tested checked good three times. Battery tested bad, bought a new one and still had the same problem. If i leave my car parked for more than 36 hours it goes dead and can not start it. Any ideas? Am going to look at the starter connections next.
05-24-2010, 11:50 AM
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When you tested the alternator did you take it out of the car and have it tested or did they just check the voltage? I would start by checking the grounds and make sure none are loose and check to see if there is no corrosion on the battery grounds.
05-24-2010, 01:27 PM
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Check your starter ground as well and check the voltage at the starter. My sisters old car did the same thing and for some reason it turned out to be a solenoid on the starter was shorting out and draining the battery.
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05-29-2010, 08:46 PM
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Im not sure the guy at pep boys just said if failed all the way across, im pretty sure it was the original starter. No i bought a new battery before having the old one tested and when i had the same problem i took the battery back then had my old one tested about a week later and it tested bad.
06-10-2010, 07:03 AM
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Alright so I put a new battery in, a new starter, kept the alternator that tested good and installed that. Battery reads 12.5 not running and running it reads 12.9 now here's the kicker batts read 13 running and 14-15 while driving if the sun goes down and the temp drops to 85ish but I live in Yuma, az so the sun has to go down for it to drop that low. Anybody have any ideas please I need help
06-10-2010, 10:39 AM
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Do you know the fix for that? Other members are having that problem that do not know the fix.
As far as the voltage dropping at idle and you have to rev it up to get the voltage to come up, thats the alternator, it wont show on a bench test. Tell them the alternator is working but not at idle you have to rev it up.
Oh and if your battery goes dead in 36 hours you have a bad battery thats not retaining charge or you have a current draw which means something is staying on that shouldnt be staying on
As far as the voltage dropping at idle and you have to rev it up to get the voltage to come up, thats the alternator, it wont show on a bench test. Tell them the alternator is working but not at idle you have to rev it up.
Oh and if your battery goes dead in 36 hours you have a bad battery thats not retaining charge or you have a current draw which means something is staying on that shouldnt be staying on
06-10-2010, 10:56 AM
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Simple, if your headlights are flickering then your alt is on its way out. One or more of the diodes in the voltage regulator is bad. An alt like this will normally pass a voltage test on the machine at the parts store, but it will fail a load test. The reason it passes the voltage test is: an alt produces AC current, and the regulator is a full wave bridge rectifier (you'll have to google that for a picture, then this will make more sense). As the juice is AC, and therefore a sinewave, you still get full voltage, but only for 50% of the charge cycle. The other 50% is something less. The meter on the testing machine can't react fast enough to pick up the down swing of voltage. But the fact is, the alt is bad. You will also see this on your in car voltmeter as the voltage has a significant dip at idle due to the 50% loss of charge cycle.
This all assumes that you don't have UD pulleys or a low idle speed. Either of those may also cause low alt output even if the alt is good just because it's not spinning fast enough.
This all assumes that you don't have UD pulleys or a low idle speed. Either of those may also cause low alt output even if the alt is good just because it's not spinning fast enough.
Last edited by fleetmgr; 06-10-2010 at 11:07 AM.
04-28-2011, 08:55 PM
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I have a 2000 camaro z28 i just had to replace the alt last week now its doing exactly what you guys are saying, reman alt isnt holding up. drops down at idle, has a small wine, works goos when its cold but as soon as it gets warm the volts drop.. so shouldi have them replace the alt for free or try and go with the 145 alt from a truck at the salvage yard?
