voltage problems?

Question

i have a 95 chev sub 5.7 l. new alternator, new battery. i am having problems keeping my battery charged. it will be at 12.8 v when i leave to go to work but when i get to work about 40 miles it will be a t 11.9 v. one thing i noticed is when i press down on the brakes the engine makes a different noise like it loses power. i am also having problems with my rear lighting. is there a corelation between braking and my battery not keeping its charge? i do have a small draw coming from somewhere but overnight it doesnt really do alot to the voltage, maybe .3-.5 loss. please list every suggestion you can think of, i mean anything.

thank you

Answer 1

I am a certified Ford & Honda service technician & I have owned about 5 or 6 of these Chevy trucks in the mid 90's models. One problem they all had in common was that the positive battery cable connections would develop severe corrosion which would usually migrate up the copper twisting into the cable itself making them develop alot of resistance. A new alternator can put out 13.7 to 15.2 volts all day long but your battery will not charge if the postive wire from the alternator to the battery is not making a clean contact with minimal resistance. The first suggestion I would agree with is to check voltage drops across each cable with a volt meter. Get some battery terminal cleaner spray and clean every connection with a wire brush. If you have large voltage drops across your cables and/or corrosion is severe enough, (lots of green & white fuzzy stuff ) don't even waste your time just replace your battery cables because you will never be able to clean out the corrosion that has seeped up inside the cables.

If your cable terminals & wires are clean and free of corrosion, the next thing you need to do is check for a parasitic draw. Get on alldata (you can get a subscription on the Autozone website) it is WAY better than a Chilton or Haynes manual. Find your fuse block diagram & power distribution wiring diagrams on there. Disconnect your negative battery terminal. Connect the clamp end of a test light to the terminal on the end of the battery cable. Then poke the end of the test light into the negative sidepost or top post on your battery. You will see the test light glow brightly. Start pulling each maxifuse one at a time in the underhood power distribution box until one of the fuses makes that light go out. This fuse or circuit breaker is going to point you to the circuit you need to start checking. Read your wiring diagram and find out what circuit that fuse belongs to. Put that fuse back in. Then reading your wiring diagram again, find the fuses in the PASSENGER COMPARTMENT FUSE BLOCK that go into THAT circuit. Start pulling them one by one, watching to see if the test light dims or goes completely out. When you find which fuse makes the light dim or go completely out. You have found the circuit drawing your battery down. Read your wiring diagram and check the wires in that circuit for a short to ground or a short to power. This is how you find a parasitic draw on your battery. It is time consuming but if you can read a wiring diagram, you can do it.

One note of caution:
There are certain modules that control things that need a small amount of power to keep memory. They are NORMAL parasitic draws. Don't be fooled by fuses that power body control modules or the ECM. These will make your test light go out too. But the trick is to watch what makes the light go DIM. Pay close attention and take your time and watch the bulb in the testlight for changes in intensity.

Electrical problems can be a pain for even the most seasoned tech. Read your wiring diagrams and get familiar with them before attempting this process. The wiring diagram is your best friend.

I hope this helps. If you have any questions feel free to email.

Answer 2

I believe b4zz about checking voltage... could be at 14.a million or so at battery without load 13.5 v a minimum of with all upload-ons on. You stated the alternator checks reliable, yet as the different stated, double verify all connections fantastically on the battery and the cable from the alternator to the starter solenoid on the sidewall.. both are very reliable factors for corrosion and excellent issues yet you are able to desire a keep to envision the completed equipment quite of only the alternator in case you probably did it off the vehicle. also in case you used a regulator from autozone , I each now and then run for the time of those who even as it is going to fee the equipment, it is going to coach undesirable on the sprint for some strange reason (i imagine the regulator has the incorrect inner voltage compared to what the vehicle needs to make certain.

Answer 3

The voltage should read 14 volts or so two seconds after the engine starts.
Either the alternator isn't working or you have a bad ground connection between the engine and the chassis. The alternator and battery are grounded to the engine and the gauge and lights are grounded to the chassis, so if you don't have a good connection between the two, you'll get those symptoms.

Answer 4

you may have a bad chasis ground or a wiring problem between the alternator and the battery. Check the voltage at the red wire on the back of the alternator and at the battery with the engine running. It should be around 14 v with no more than .1v drop between the alternator and the battery.

Answer 5

Ok, it is a fact, that if the altornator is working properly, it will always put out 13.5 to 14.5MAX voltage.a reading of 12.8voltsDc comes from a fully charged battery, before the engine is started.now, if you are getting that 12.8 volt reading while the engine is running, your altornator is not working.
a new altornator can go bad in a moment or after many years. but if there is a wireing problem, and if it affects the field that powers the alt.. you could be blowing the internal regulator., making that altornator, JUNK

Answer 6

check wiring to taillights could have short if somebody wired up for trailer