Voltage gauge holds steady at 13.0 - issue?

[ZZ13]

The port voltage gauge holds at 13.0. (Starboard reads 13.5) on my Cummins 6cta. Looks like both engines have newly installed reman alternators and new belts. Is this within gauge accuracy tolerance or is there a problem?

 

[sdarc]

Take a voltage reading from each of the alternators or voltage regulators when running. If they read close to what you're getting on the gauge you good to go.

 

[SloBurn]

Usually dash gauges are not very accurate. Measure outputs with a voltmeter to be sure.

 

[JimG]

Normally you should see the voltage rise (to near 14VDC) when you increase RPM's... this is an indication the alternators are charging.

 

[ZZ13]

So I've been chasing this for a while and it actually got worse. Port side would idle around 12.5V. If I gave it throttle up to 1500rpm, no change. I could get it to 14V when cruising at 2200rpm. I finally took time to debug it. I disconnected the power cable from the alternator and started up the engine. When I measured the alternator output at idle - nothing. No voltage. I guess there is a chance the belt is loose. But I think I am looking at replacing the alternator. Also, starboard is rock solid putting out 13.85V at the alternator at idle.

For you diesel folks, I first disconnected the air intake heating grid to make sure it wasn't dragging all the current at low rpm. But I don't think the grid was working anyway because I never could get any kind of voltage reading out of it.

 

[ZZ13]

I found the problem. The main grounding cable connections to the engine block were compromised from a salt water leak that occurred during previous ownership. Took off and cleaned the contacts really well. 12v voltages are as expected at idle and with a little throttle now.

Update: turns out the alternator was intermittently failing and eventually completely shut down for good. I had to replace the alternator.

6 month later update: Now with the new alternator, it consistently put out 13.8v. Didn't seem to want to back off of that. Then, I decided to buy new batteries because they were getting hold. Lo and behold when I lifted off the terminal cover I found a ground connector not bolted onto the battery post. The bolt was missing. The connection was very loose. Tightened it down and the alternator charges exactly like it should based on need. Bad ground was the right track all along.

 

[hottoddie]

Did it correct the problem with the air horn?

 

[ZZ13]

No. The air horn problem turned out to be a dirty reed inside the horn. That's all fixed now as well.