After driving for about a mile or 2, my voltage drops from 14 to 11.6 volts in a matter of seconds while driving and at idle, usually after the car shifts gears. If I turn it off and restart, it always goes right back to 14 volts and does the same thing all over. I bought a 220 amp power master about 5 months ago. I checked all grounds as well. Starter and battery are good. Any suggestions? Does this sound like the alternator went bad already? I did have it tested at o'Reilly's but not when it was registering at the 11.6 volts. The test came back good but again, the volts were at 14 volts when tested.. Thanks for any feedback.

 

Car first stated, lights,Ac, radiator fan off, what is the DC reading of the alternator using it body as the ground, and back terminal under the rubber boot as the postive source?

If holding constant at around 14.7 volts, then start looking for problems down line, hence loose starter solenoid connector where the battery and alternator cable come together, the ground bolt connector to the engine right above the starter, and the nut on the engine fuse box terminal.
Hence when checked with the above conditions, alternator should be at 14.7, battery terminals at 14.5, and engine fuse block terminal as positive , and alternator body as negative, should be 14.5 as well. If these are good, but DIC voltage is showing less than 14.1~14.3 then you have a problem from the engine fuse block termial, to the BCM, and then down line to the ECM. Hence DIC and dash gauge voltage meter, is telling you the voltage at the ECM (not at the dash gauges), which is end of line after the BCM.

As for the 220amp alternator, what was added to increase the alternator to this size, and are you sure that the alternator is able to keep up with the demand of the added electrical equipment?

Last one, and although this write up for a OEM alternator, it can be used for after markets as well. Hence loose bolts/nuts or corroded terminal connections, brushes that are either worn out or sticking in the brush cage, and so forth that can explain the drop in voltage once the alternator metal does start to warm up.

https://www.corvetteforum.com/forums...nator-fix.html

 

Thanks for the reply, I did check all of the options above. All look good. Nothing is loose or corroded, especially corroded all is clean. I would also think if this was the issue, wouldn't it start at low voltage? The alternator is only 5 months old and I have not had any voltage drops until recently. The strange part is, it happens right after a shift point? Once it shifts, the volts drop from 14.1 to 11.6 almost automatically? Why after a shift point? Then I come to a complete stop, turn it off and restart and bam, it starts at 14 volts again? I have an aftermarket sub, amp, and speakers along with radio. I want to say about 600 amp. It's definitely powerful but it shouldn't kill the alternator. Can the transmission have something to do with it? Is it odd that it drops volts right after a shift?

 

Just did it again, shut it off, started, went right to 14 volts? Then drops to 11.6 volts, turned it off and back to 14 volts. What the frick.

 

When it drops to 11.6 volts ,start checking voltages on the charging system side under the hood.

This will weed out if the problem is in the charging system or after the charging system from the Engine fuse block back.

And again, DIC is telling your ECM voltages, so problem could be a simple at a ECM ground or connector corrosion pin problem if not up in the charging system portion of the car.

 

Thanks, that's exactly what I did today. I drove it around until it dropped then drove it to autozone. They plugged up the cables to the battery and the rep said the alternator was kicking out 11.6 volts. I turned off the car and restarted right away and it went right back to the 14 volts and the meter read that as well. So weird.. It has to be something with the alternator. Maybe the regulator?

 

Maybe on voltage regulator or brush sticking in the housing, or could be the voltage sensing circuits from the engine fuse box, or ECM control circuit the problem causing the alternator to drop voltage instead.

 

I disconnected the plug into the ecm, cleaned it with electrical cleaner, brushed it, and the same thing is going on. Are you saying the ecm can be going bad?

 

Could be, or enough RFI noise to the ECM from the coils, via after market spark plugs or spark plug wires, to cause the ECM to clip the output voltage on the alternator instead.

You don't list your location, but if you're in the Denver area, could have you bring it over to the house to get you squared away in a few hours.

 

Thanks, I'm in a suburb of Chicago. I wish I could swing it by. I changed the wires and plugs about 3 years ago. No issues and oem.. This problem just started out of nowhere..

 

Do you still have the OEM alternator and is it operational? If so, I'd disconnect the amp, replace the PowerMaster with the OEM and see if that works normally. That would help in sectionalizing the fault.

 

I do, I will give it a shot tomorrow.. Thanks..

 

So I ended up buying a gm alternator, amazon prime. Installed in a half hour since I'm a pro at this going thru 3 crap alternators, and bam, 14.4 volts STEADY.. The power master held at 13.9 and has more amperage per the advertising?? I will never buy aftermarket or rebuilt again no matter what amperage is advertised.

 

Glad you got it sorted out. Did the Power Master come with any warranty? I'd have thought at least 6 months, more likely a year. Are you going back after them for either a refund, or replacement?

 

Thanks. I sent it back for a refund. I had to go thru a few holes but in the end, I was able to plead my case. I would not take a replacement. I will be keeping an eye on the refund process.