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Old 09-22-2010, 04:25 AM   #1 (permalink)
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A good way to check alternator?

My truck is a 2006 with original batteries and lately has been taking longer to turn over. Now, the batteries barely have enough charge to turn the engine over.

So I'm thinking it's the batteries, but i wanted to check the alternator first. I used to disconnect the battery with the car running. If the car stayed running then you knew your alternator was good. If I do this to my truck will I damage the computer or something? I've read on some cars you're not supposed to do that. So has anyone tried this old trick or do you have a better way to check the alternator? I don't trust o-riely or autozone as they usually get it wrong.

Thanks.
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Old 09-22-2010, 08:34 AM   #2 (permalink)
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Take a LONG screwdriver, while its running and lay the metal part across the pulley face and if the Alt is creating Voltage it will attract the metal shaft to the pulley because its a magnetic field.
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Old 09-22-2010, 10:13 AM   #3 (permalink)
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Just put a voltage meter at the batt cables the Alt should be putting out 14.5 volts to the Batteries.
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Old 09-22-2010, 10:22 AM   #4 (permalink)
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Quote:
Originally Posted by CAR67 View Post
My truck is a 2006 with original batteries and lately has been taking longer to turn over. Now, the batteries barely have enough charge to turn the engine over.

So I'm thinking it's the batteries, but i wanted to check the alternator first. I used to disconnect the battery with the car running. If the car stayed running then you knew your alternator was good. If I do this to my truck will I damage the computer or something? I've read on some cars you're not supposed to do that. So has anyone tried this old trick or do you have a better way to check the alternator? I don't trust o-riely or autozone as they usually get it wrong.

Thanks.

IMO you have a battery or batteries going out. I would not suggest pulling the cables while running, the voltage might rise fast and mess something expensive up. It not worth the risk IMO!

I'd check the voltage after it's been running for a few minutes. It should be ~13.6-14.2 volts. If you are in this range the alt is charging.
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Old 09-22-2010, 10:26 AM   #5 (permalink)
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+1 on volt meter. You can pick them up real cheap at places like walmart. Pulling the cables won't work as well on a diesel since theres no spark. You would have to pull them and wait long enough for the battery to go dead enough that the computer couldn't "think" any more to fire the injectors. That slow drop in voltage could be bad for it.
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Old 09-22-2010, 12:06 PM   #6 (permalink)
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Thanks guys, I appreciate it. I do have a voltmeter, so I will try that.

Thanks again.
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Old 09-22-2010, 09:11 PM   #7 (permalink)
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Also, while you have the meter on there, check for AC voltage. Anything over 0.3 volts AC is a sign of the diodes in the alternator failing.
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Old 09-25-2010, 02:26 PM   #8 (permalink)
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Short story: I think it was dirty battery terminals

Long story: see below
~~~~~~~~~~~~~~~~~

I had to get a jump to get the truck started. I checked the voltage with a meter, just like y'all suggested. Got 14.25. I also had two codes in, one said intermitant power to the ECM. Cleared the codes.

I then drove around to see if the batteries would take some charge. Came back home, turned it off, then back on. It seemed that they did take a bit of charge because the engine turned right over.

So shut it down. Cleaned the cable terminals. The passenger side had a bit of corrosion, but nothing you could see with the terminal on the post. I sprayed some terminal lubricant on them. Took another drive, this time with my code reader on. It also read 14.2 - 14.5 volts, even with bright lights on, interior lights on, voltage never dropped below 14.2

So I think my problem was just dirty terminals, even though they sure didn't look dirty. My budget is really tight right now. Most times, i would just go ahead and get new batteries, especially since they are probably running on borrowed time, but right now, i gotta save where I can.

Thanks again to all those who replyed.
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Old 09-26-2010, 10:26 AM   #9 (permalink)
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Any good shop will be able to load test your batteries with a carbon pile type machine and evaluate your alternater output with the same tester.Some may even do it for free. The DVOM voltage test doesn't really tell the whole story.
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Old 09-26-2010, 11:01 PM   #10 (permalink)
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Another thing to do would be to actually put your batteries on a charger and let them take a charge... charge them separately (disconnected from the truck) and then let them sit off the charger overnight.

Their voltage alone will tell you their health at that point.



Keep in mind, the above is only applicable after they've had time to sit at rest with no additional charge or discharge after the charger indicates they are fully charged.
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Old 09-30-2010, 12:28 AM   #11 (permalink)
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Take it to AutoZone etc and they should be able to test it for you.
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Old 10-18-2010, 09:20 AM   #12 (permalink)
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This is just a follow up....

My truck did not want to start this past Thursday, so that's about 3 weeks since I reported the problem.

The oem batteries both had bulged sides, i'm sure not normal, but not sure what that means either. I took them to autozone and had them tested, one was bad and other was "probably bad".

I finally broke down and bought two Autozone Gold series 65 DLG for $105 each. It rated second overall in Consumer reports testing and has a 3 year free replacement and 8 year pro-rated warranty, and 850 CCA. Oem was 750 CCA. Now the engine cranks over very quickly!!

I would liked to have bought the Sear Platinum as that battery was rated tops in CR and is actually made by Odessey for $180 each, but like i said I am on a tight budget right now. The Sears Platinum are actually quite a bargain compared to the Odessey which is sold for ~$280 each. Same specs and same battery, so if you have the cash, I think it would be worth the upgrade.

Thanks to everyone that chimed in. I appreciate your help!
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Last edited by CAR67; 10-18-2010 at 09:23 AM.
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