Electrical Issue? 2007 5.7L

2007 Tundra CrewMax 5.7L 216k miles.

Several months ago I noticed my voltage meter jumping around once the truck warmed up, along with interior and exterior lights flickering. It only does it at idle or low RPM. I assumed it was the alternator and replaced it. It did not fix the issue. I also tried cleaning the battery terminals and connections. I replaced the ground wire going from the battery to the fender. No difference. The serpentine belt looks fine.

Since it didn't seem to be draining the battery, and never left me stranded, I decided to just live with it. However, it has now stalled out twice while I was driving at low RPM. No check engine light and no troubles restarting, so I'm assuming it lost power for a brief second.

Everything I've been reading suggests a bad ground or a bad electrical connection. I was able to find one ground wire strap, which was by the 02 sensor. Where else should I be looking? How is the alternator grounded? That seems like a good place to start. Any other ideas or suggestions?

 

My next step would be a load test of your battery if you haven’t already. Just because it cranks and starts doesn’t mean it’s OK.

 

Another vote for battery test.

 

Thank you both. They say my battery and alternator both test good. Just out of curiosity, I swapped my battery with my dad's Tundra battery and it did the same thing.

BUT it did something weird when we put his battery back in his truck. His voltmeter read very low but would go back up to the halfway point when he revved his engine. He drove it for a few miles before it went back to normal. We had his truck tested after that and both the battery and alternator tested fine. Does this suggest I have a drain on the battery? And perhaps the alternator is only able to compensate at higher RPM's? If so, I would think my battery would have a low reading with a multimeter but it doesn't.

 

Maybe your battery to ground connection is bad. This would be cause for both batteries not getting a good charge. Have you tried to start the truck, increase throttle just a hair, and disconnect the battery to see if it can run off the alternator alone?

 

Just saw you replaced the ground to battery. Are you sure that the alternator is grounded well. Maybe the mating surface was dirty and corroded when you installed the new one???

 

This is a very bad idea for any modern vehicle, in doing that you’re welcoming a voltage surge that could get very costly replacing ECU’s and other electronics. This ain’t the ‘70s anymore.

 

Voltage drop testing of all main cables including grounds would be the next place I’d go.

https://m.youtube.com/watch?v=qPpHRuddhh4

 

Update: I hooked up a jumper cable from the alternator to the battery ground and that made no difference. I then tried the jumper cable from the battery ground to the frame which also made no difference.

I will try the multimeter testing next chance I get.

 

Update: I took it to an electrical mechanic and he diagnosed it as a faulty alternator. If correct, that means it was faulty right out of the box. I'll try having it replaced under warranty and will report back if that solves the issue. I can't wait to do that job again...

 

Up above I thought you said that the alternator tested good. I can't wait to see what happens when you get it swapped out. Good luck! Hope it is in fact defective so you can at least be done. Could you have a bad belt tensioner and it isn't spinning fast enough due to slipping belt? Maybe time to make sure before you get busy taking it apart.

 

Well I probably should have mentioned it tested good when it was bench tested, but it failed when it was installed. They said the voltage regulator was bad, which I assume is because the tool could tell it was fluctuating. But I thought the bench test was probably more reliable. Maybe I'm wrong about that.

I am in NO hurry to replace the alternator AGAIN. I wondered about the belt and/or tensioner but I don't hear any weird noises, don't see any wear or slipping, and all other components, such as the a/c, seem to be working just fine. I am definitely ready to be done with this.

 

Definitely sucks!

 

Have you taken a multimeter and measured voltage across the battery terminals as the truck was running.

This should have been the first step.

You want a strong 12v with the truck off and a steady 13.5-14v with it running. If it is jumping all over the place and spiking over 14v the voltage regulator is shot.

If you are getting 12v while the truck is running then the alternator is simply not charging.

 

Final update: I had the original alternator and the replacement alternator bench tested at the local parts store and supposedly they both passed.

I still went ahead and did a warranty replacement. The replacement solved my problem. No more dancing volt meter. I'm getting a steady 13.45V at idle and no more flickering lights. Thanks everyone for helping me troubleshoot!