Alternator problem????

[Purpledoggy]

Please bear with me as I'm a woman trying to figure out manly stuff lol! While driving my 03 yukon denali to work I noticed the voltmeter drop from 14 to 12 while on the freeway with the heater, heated seat and radio on. The drop was enough that it felt like I was loosing power but the interior dash lights did not dim. My dad had the truck last night and I noticed when he brought it back the lights would brighten whenever the rpms went up in the engine. When I was heading home from work I decided to see if the problem would persist so I turned on the radio, heater and heated seats and while I was sitting in traffic the voltage again dropped this time to the point the truck started to stall while at idle. When I turned off everything it seemed to be stable and gave me no other problems for the ride home. I'm afraid to drive it now because I'm not sure what is wrong. My dad also said it stalled on him when he put it in reverse but I did not have this problem. The battery is new because the old battery that was in it died after sitting for a few days so I figured it was bad anyway. I'm starting to think now it might be the alternator instead. Has anyone had a similar problem? All I can think of is an alternator issue but I'm not used to these vehicles. My dad is busy trying to get his plow on his truck so I'm trying to figure out what could be the problem so I can hopefully troubleshoot it and get it fixed. Any help????

 

[TxDrewski]

Check the jump connection. Theres a positive lead with a nut and bolt where your supposed to put the positive cable to jump start someone. That nut backs off and then your alternator only charges part of the time.

Get a cheap volt meter and see what your battery is reading with the car on.

Pull the battery off and the alternator and have them both load tested.

In no particular order

 

[Purpledoggy]

Where can I get a voltmeter from? I'm guessing any auto part store?

 

[TxDrewski]

Where can I get a voltmeter from? I'm guessing any auto part store?

Or harbor freight, walmart k mart etc etc. They are usually 10-20 bucks and worth their weight in gold.

---------- Post added at 10:54 PM ---------- Previous post was at 10:51 PM ----------

But first check that lead jump off point. Id also start the truck and let it run for a few and then disconnect the battery and see if it dies.

 

[Purpledoggy]

I didn't think about harbor freight. I will try to hit them up tomorrow! Is there anything else you think I should/can test?

 

[TxDrewski]

But first check that lead jump off point. Id also start the truck and let it run for a few and then disconnect the battery and see if it dies.

 

[OHSIXX]

Check connections on the battery and the alternator and ground. Look for corosion. As mentioned above-use a VOM to check voltages with the truck off and on. Should see 12.5-13 DC with it off and over 14 volts DC with it running.

Most auto parts stores or a auto repair should can do a load test on your battery as well as check your alternator to make sure it is operating correctly.

 

[Physh1]

Sounds like your alternator is failing under load. Have it bench load tested to verify.

 

[OR VietVet]

X2. Alternator starting to go. Make sure when do the work that you also check all connections at the battery for cleanliness and tight. Make sure the belts are in good shape also. A slipping belt can cause same problem but is more rare than a failing alternator.

 

[Purpledoggy]

Thank you for the info. Hopefully I can get under the hood and check it today if I get off of work on time.

 

[Xypher]

My wife's 02 Tahoe has similar dips in power, but not to the point of stalling. It was the belt tensioner. What the other have said seems more probable, but just another option if those turn out ok.

 

[Purpledoggy]

So I have another question. If I get a new alternator apparently there is a 105 amp one and a 145 amp one that fit my vehicle. Which one should I get? Does it matter?

 

[OR VietVet]

Does matter. Look at the casing of the alternator and you should see it etched in the metal. Typically can see even when mounted on vehicle.

---------- Post added at 10:05 AM ---------- Previous post was at 10:04 AM ----------

May have to use finger/thumb and spit to clean and see or the girls way of using a damp cloth to wipe clean!

 

[Purpledoggy]

Where on the alternator does it tell you which it is? I'm guessing it's hidden under the engine cover because I couldn't find it.

 

[Mr. 960]

It should be engraved right on top. Like others have mentioned it is probably covered in dirt. Being it is a denali it most likely has the 145 or 160 amp. Both the 145 and 160 use the longer belt. the 125 has the smaller belt. I'd be cautious to test the alternator the old school way of pulling the battery cable while running the engine. I've heard you could fry your computer like this on the newer more sophisticated cars.

---------- Post added at 01:42 AM ---------- Previous post was at 01:39 AM ----------

So I have another question. If I get a new alternator apparently there is a 105 amp one and a 145 amp one that fit my vehicle. Which one should I get? Does it matter?

yes 105 will not be enough amps when you have all accessories running. the voltage will drop considerably.

 

[OR VietVet]

Where on the alternator does it tell you which it is? I'm guessing it's hidden under the engine cover because I couldn't find it.

Like I said, the number should be etched in the case of the alternator housing on a flat area that is exposed and will be dirty in all likelihood. It will not stand out like black lettering on white. It is just etched in to the aluminum and will help if you have a flashlight.

 

[Purpledoggy]

I wiped off the top of the alternator but didn't see a number. I found the parts code in the glove box and found out it has a 145amp alternator. I'm going to try and mess with it all when I get off of work tomorrow morning. Let's hope I can manage to fix my problem lol!

 

[OR VietVet]

If you never find that etched amp rating, guarantee it is there if original alternator, then the alternator was changed before and the rebuilder of the alternator that was changed out to never installed the same case back on the alternator when rebuilt. But as I said, it is there if is the original alternator. Do you have the serpentine belt tool or any tools to relieve the belt tension with the belt tensioner to allow the belt removal for access to alternator? You will need that and then the tools to remove/replace the alternator with. Suggest you disconnect the battery before removing the alternator wiring. Make sure the electrical connector is clean before plugging back in to new alternator.

 

[Purpledoggy]

I use my dad's garage and his tools. This will be the third alternator I've replaced in my life. One from my mustang and one from my camry. I'm not worried about actually replacing it I was worried that it might not be the problem.

 

[OR VietVet]

Good luck. Sounds like you have the experience part down pat.