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Is my alternator going bad or is it something else?
So this is a new issue. I was heading to a early morning car show yesterday and the check gauges came on. The car was full of gas, Had oil pressure and wasn't hot. The Alternator gauge had dropped to roughly 10 amps it would hang out there for a little bit maybe 1-2 minutes and then jump back up to its normal 15. It did this multiple times. I tried to get some good pictures of it doing it, but I was running down the freeway. Has anyone had this happen? I read it might also be a bad ground. What are your thoughts on it?
That left needle is not measuring amps, its a voltage meter. And yes, its considerably low. What year of vehicle? GM back some years ago went to a dynamic voltage control method with their alternators to increase fuel mileage but that more or less 10 volts DC number in your picture is low, even for that GM fuel savings method.
If you see that situation again, check the DC voltage with the engine running at the battery. While you are there, flip the multimeter **** to AC volts to see if you have any alternating current diode leakage out of the alternator.- this should be a very low number around .05 volts AC and might jump a little. Maybe its a bad gauge, bad instrument panel cluster, bad alternator and far less likely, a bad PCM. Could also be a dying battery with an intermittent dead cell.
That left needle is not measuring amps, its a voltage meter. And yes, its considerably low. What year of vehicle? GM back some years ago went to a dynamic voltage control method with their alternators to increase fuel mileage but that more or less 10 volts DC number in your picture is low, even for that GM fuel savings method.
If you see that situation again, check the voltage at the battery with the engine running at the battery. While you are there, flip the multimeter **** to AC volts to see if you have any alternating current diode leakage out of the alternator.- this should be a very low number around .05 volts AC and might jump a little. Maybe its a bad gauge, bad instrument panel cluster, bad alternator and far less likely, a bad PCM. Could also be a dying battery with an intermittent dead cell.
Rick
Thanks Rick it is a 2002. This was the first time it did it and it only did it going down the road. Idling at the show or at home it was fine. I need to add the dash lights did dim a bit when the gauge dropped.
Thank you for this. Mine is doing it going down the road not at idle so opposite of yours. The motor was just installed, so I guess I need to check and make sure the ground are clean and tight. I do have the belt tensioner noise very briefly when its been sitting for several days. Looks like I need to address that as well.
Mine is staying up and then it will just randomly drop for a minute or two and then its fine for 10 minutes or so.
Yeah it’s possible it’s something else, take what I said with a grain of salt.
I was just describing my situation in my truck which is similar to what yours is doing. In the end it did end up being my alternator. After a while, It got to the point to where it just stopped charging.
Maybe take a look at the exitor wire and check the connection on that.
I added the Hawks Third Gen exitor extension, a little thicker gauge wire with a new connector
Yeah it’s possible it’s something else, take what I said with a grain of salt.
I was just describing my situation in my truck which is similar to what yours is doing. In the end it did end up being my alternator. After a while, It got to the point to where it just stopped charging.
Maybe take a look at the exitor wire and check the connection on that.
I added the Hawks Third Gen exitor extension, a little thicker gauge wire with a new connector
Kids start school tomorrow so I will have a lot more free time to dig into it. I will check the exitor wire and connection. I just dont want to get off at a show and it wont start lol. I did have my wife bring my jumper pack to me, but I want this fix asap lol.
I will run it up there tomorrow after the kids go to school and have them test it. Are we thinking powermaster or which one seems to be the best? I have a Napa, Orliey, kind of a drive but, Summit, Autozone, and Advanced Auto Parts. I hit this back in the day with my Foxbody. I bought a Autozone replacement and 3 of them were junk before I got a good one. I want to say I had to get a motorcraft unit from them. I ended up paying a lot more.
I would never buy another alternator that was not either OEM or from Powermaster. Too many disappointments with everything else. Powermaster is a better value than OEM at this point, especially because you don't really know what you're getting over the GM parts counter these days for an older application like this.
I get junk yard original GM starters and alternators rebuilt by a local reputable shop. They work very well but I wait three days for the repairs to occur.
The car is not a daily so it can sit for however long. I will have to go get it checked tomorrow. I didn't realize how busy my day was going to be. I will just drop the boys off in it tomorrow morning and then run up to auto zone. I will have to figure out who rebuilds them in DFW. Summit had one Powermaster left so it may or may not be available.
Well the alternator is checking out fine. So now on to the ground straps. Where all do I need to check. Back of the passenger head, driver side on the block under car. Anywhere else? Exciter wire what voltage do I need to be at? They basically said its good, but it could be going bad... That is how it tested lol. I drove it for about 30 minutes today around town and it never once did it again.
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Is my alternator going bad or is it something else? 
