I've noticed my alternator doesn't charge at a steady rate. Idling or driving down the freeway the voltage is constantly going up and down. Almost like the alternator is turning on and off. For example: idling voltage will stay at 13.5 for a few seconds and then drops to 11.8-12 for a few seconds and so on and so on, then driving down the freeway voltage will be at 14 for a few seconds then drops to 13 and on and on. Is this normal or is my alternator taking a ****? I replaced the battery a couple months ago.

 

somethings wrong, that being said go to one of the auto parts stores that offer free testing and maybe code reading. voltage will drop at idle with everything running but at RPM you should see it hold steady

 

Thanks. That's what I was thinking.. I'm gonna to take it off and have it tested tomorrow.

 

Don't take it off, just bring the whole car in. They can test it that way.

 

Another thing to check is the wiring harness to the alternator. Mine was routed so tightly around a bracket, it was starting to cut itself open to expose the copper wires inside it.
Double check the back of the alternator for possibly a loose connection.

 

Also try checking the HORN/ALT SENS fuse in the fuse block under the hood. I found mine blown after my alternator took a dump. I don't know which failed first (fuse or alt), but it's a quick check/fix.

 

AC kicking on, will kick the fan on too, and pulls more power away from the battery.

Problem sounds more like a bad charging system wiring connection problem to start with, and when the a/c and radiator fan kicks on, it making the problem worse.

The positive wire comes off the back of the alternator, connects to a terminal on the starter, then a second wired comes off the start and connects to the battery. From the battery, this is another wire that connects to the fuse box terminal.

On the negative side, the main ground comes off the battery, and connects to the engine block just above the starter. Also, then is a smaller wire that comes off the negative battery terminal and connects to the chassis just before the battery.

Hence all these connections should be cleaned (including the connections to the battery), a little dielectric grease applied to the connectors and then the bolted back on to there connection spots.

As for a quick test to see which charging wiring connectors are the problem, with the motor idling. A/C off, and a multi meter set to DC.

Check the alternator output voltage. Use the terminal on the back of under the rubber plug as your positive source (make sure you are on the terminal and not the wire connector), and use the body of the alternator as your negative ground source. The voltage should be 14.6V.

If the voltage is lower, don't panic yet, since I did a quick write up on pulling the alternator apart to clean it up to solve most of its problems. Also to note, double check the spark plug wires and the spark plugs to confirm that they are OEM. some of the after market plugs and wires do not have the needed resistance to RF suppress, and it can cause problem with RF interference back to the ECM that is controlling the output of the alternator (read will cause low voltage).


Now take a reading at the battery terminal, and the voltage should be 14.5. If the voltage is low, the supect either the postive connection port on the starter for the postive wires, or the ground wire to the engine block.

Take a last reading off the fuse bolt postive terminal, and use the body of the altinator as your ground source. The voltage should 14.5, and will tell you if the problem is the ground wire off the battery to the engine block if your voltage was low lower than 14.5 at the battery instead.

As for if the voltage at the battery is 14.5 volt, then the DIC should give a reading of around 14.2 ~14.3 volts. The DIC is reading the voltage of the BCM/ECM, which is sending a digital signal back to the DIC to read their voltage (DIC is not telling you the voltage to the dash itself, since athough it has dials, it all digital instead). Hence with the amount of wiring between the engine fuse box to the BCM, then to the ECM from the BCM, it normal to have the .3 drop in voltage to them.

As for when the car is idling and the ac/radiator fan kicks on, should still hold to about 14.0 volt or better, if all the charging wire connector points are clean and tight.

List your voltages, and I can tell you where the problem is to begin with/what to focus on.

And forget taking the car to an auto parts store, since all they will be able to tell you if is the battery has a dead cell alone. Problems in the charging wiring connection points ends up just confusing them like the alternator is bad isntead.

To add, if you find out that one of your starter solenoid terminals is bad or cracking off (read headers without a heat shield on the starter or someone over tightened the nuts to crack the Solenoid), we have you covered for under $30 to solve the problem (hence just replace the starter solenoid).



https://www.amazon.com/Premium-Quali...iglink20400-20

 

I replaced my factory alternator with a Billet-Tec, more for looks than performance, but I have to say that it stays steady at 14.2 no matter what is running or what the RPMs are, idle, with air, Idle with air and fans, etc, always 14.2 and I have an underdrive pulley on the car as well, so it it turning even slower at idle than GM intended.

 

A worth while upgrade for our power hungry cars....

 

It's is worse with the a/c and fans on, but its acting like an on off switch. You can watch the volt gauge bonce up and down.

 

I think that you need to have the voltage checked to verify that the big swing in the readings is originating from the alternator.

 

I checked it with a volt meter. Its steady as can be at the alternator, under hood fuse box, and battery between 13.8-14.0. It must have be where the DIC is reading from.

 

You might have saved yourself the cost of a alternator...
But, looks like more work to figure this one out.

 

I need the actual volt reading from each of the points, and not just a range of the points readings instead. This will weed down where the problem is to start with, and why the problem is getting worse as the engine heats up (metal starts to expand).

 

Cool! Here you go-
At idle with a/c on
Post on alternator- 14.4
Battery- 13.98
Post on fuse box- 13.67 (the D3PE fans are connected to this)

 

Just went through something similar. In my case it was that my tuner replaced stock Spark Plugs with Nickel electrode. Do a search, if this is what happened in your case go back to Stock Iridium Delcos. If not Iridium it pulls way more spark and alternator appears to be going haywire !!

Btw, before I switched back to Stock Iridiums went to local auto shop and they ran a test that said my alternator was dead. With plugs back in I'm back at 14.2 solid with only slight dip at times.

 

Life made easy.
Alternator needs to be pulled apart and cleaned (make sure to flush out the Brushing housing to remove the dust from there as well). When you are putting the voltage regulator back on, make sure to clean and grease the contacts as I pointed out in my write-up with the Q tips.
This will bump the voltage back up to a strong 14.6V range.

Next, You have major problems with the positive wire connectors on the starter starter solenoid post terminals. Hence the wire connectors on it need to be pulled, cleaned greases, and put back on with the nut tight. Again, the voltage drop from the alternator, to the battery should only be a .1 volt drop due to the lenght of wire from the alternator to the battery (with the connection point on the starter solenoid for the two wires).

Ditto with cleaning up the fuse box connector cable point and making sure that the bolt is tight as well.
Note, on the positive cable off the battery terminal to the fuse box, light it up with some cleaner at the battery connection point to the cable as well. With the major voltage drop the battery to the fuse block, may have some corrosion on it to the battery connector that is causing the major voltage drop instead.


As for the ground cable to the engine block, looks OK since you have a higher voltage at the battery terminal, then you do have from the fuse block to the Alternator ground, but not a bad idea to go ahead and remove and clean it's connection point at the block as well, since it right above the starter and your going to working there anyways on the positive wire connector points.

Once you get all these cleaned up, greased, and re-connected, then post back with your voltages again (should be 14.6, 14.5 and 14.5 with the A/C OFF), and tell me what the DIC reading is a well (should be 14.2~14.3V, and if lower, then we need to get into pulling the engine fuse box apart to clean it's upper and lower block, then maybe even the connectors to the BCM and ECM as well).
Note, with your two fans, and the AC on, the DIC voltage should be about 14 volts instead. Also, double check the battery to make sure you have not started to kill it with the charging system not working correctlly , but with it on a tender/fully charged and the tender just disconnected, the battery voltage with the car not running/car still in sleep mode should be about 13.7 volts. If you are coming up with a lower voltage fresh off the tender and the car still in sleep mode, then some of the battery cells have taken a hit instead.

Note, the upper fuse block is a snap to pull via the 4 bolts, to clean it up, grease it and the lower fuse blocks as well.

Ditto on the BCM and ECM as well.


To rub some salt in the would, welcome to high humidity, and the fact that GM could have solved all these contact gremlin problem by just using some dielectric grease on the connectors when they where putting the car together to begin with instead.

 

I can't use factory plugs due to supercharger. I run #7 NGK's.

 

Great! I'll work on it today and see what I come up with.
Thanks

 

Thank you for this much amount of information. Sounds like something I need to do this weekend. At highway speeds I'm always sitting at an average voltage of 13.8 on the DIC.
Then while sitting in stop and go traffic, it fluctuates between 11-13 volts.