For the last few years I have had a bit of an issue with my 2003 350Z and the voltage gauge reading low. It starts off fine and then starts to drop a bit. If the car is running at anything above idle it is fine. Reading around 14 or so. When you depress the brakes it falls quite a bit into the 12.5 range. It does the same thing when I use the lights as well. I have replace the battery and the alternator a few weeks ago but this has not helped the problem.... Any ideas on what it could be?

THANKS I need the help on this one...

 

The first thing I would do is get a multimeter and look at the voltages across the battery to verify that the gauge is giving you accurate information. Verify that first before digging into the electrical system.

 

I have put the system on a meter the voltages I have given are accurate

 

Clarification:

When the car is not idling, rpm above 1500, you have no issues?

If you're cruising down the road, turn everything on: fans, lights, step on the brake, the voltage remains at 14?

Voltage only drops when idling?

 

The car has no issues when the rpm is above 1000rpm with lights fan defrost or brakes on. Once the rpm drops the voltage drops.... I have no idea. other then when it is cold it runs at the proper voltage once the car starts to warm up and run for awhile it has issues....

 

Weird,

I'll have to do some research because I am not seeing the easy answer, it should be there.

 

I am thinking it may be the wire from the alternator to the battery is an issue or possibly the fuse able link. But I am open to any and all suggestions!!


Thanks

 

Check the lead from the Alternator to the battery. also check the ground. it might be corroded and not making a good ground.

 

I did some reading and it is common for alternators to need to be at 1000rpms before being able to supply full voltage under full current load.

That being said, you may be fine. What caused you to replace the battery and alternator?

 

Battery light was coming on and the battery was not charging. I thought to replace both would be prudent.... I will see how it runs today. It almost seems like it may be something in the charging circuit. I just do not want to keep throwing parts at it.

 

You probably need to start cleaning connection points within the charging circuit. Not fun, but there is definitely resistance in the circuit somewhere and corrosion is your most likely source.

It is possible for a fusible link to fail halfway, leaving your circuit with a high resistance choke point.

 

Nissan put the Voltage gauge and oil press gauge only for decorations. They are not accurate.

 

That is why I have been using a digital volt meter well trying to diagnose the issue.

 

Car has been working well. It still has a bit of a drop when I hit the brakes but not going below 12 volts or having issues with the charging light coming on. I think I will replace the cables and maybe the fuseable link. This is the second alternator and the issue still persists. But not as bad as originally so running out of ideas a bit.