Hey guys, so I have a weird alternator issue or what I believe to be the alternator. It will not charge randomly for a period of time. First time I noticed it was on my way to work. I got about 6 miles from my house when I realized my lights went dim every time I was in the throttle a little bit. I let off and they came back brighter. Lasted about 20 minutes. I was only showing 12.2 volts on Torque Pro and then it went to 13.8v. The dash guage was normal with no fluctuation. On my way home a couple days later it lasted almost 30 minutes until it charged 13.8. Yesterday, it only did it for a few minutes in the driveway. Any ideas? Hate to shell out money for an alternator if thats not the issue.

 

You can start by checking the plug on the alternator making sure it’s completely plugged in, Grounds are clean, nut is tight on the alternator, belt is in good condition. If that all checks out, have the alternator tested.

 

Voltage regulator was faulty when my van was overcharging,you can try to change it first.
Inexpensive compared to new alternator,if alternator is faulty,then you have new regulator for the future..

 

I will check those. The lug is tight as is the plug. Belt is ok, but I think I'm gonna swap it for a spare I have that's in better shape. I'll look at the grounds as well and see if I can get them clean.

 

Let me add, unplug it and look for any burnt pins or corrosion...

 

If your glow plug relay or your AIH kicks in randomly, it will give those exact same symptoms.
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I just got bit by a corroded ground cable on the passenger side of my son's truck. He put an alternator on it and it still would not charge. The cable was tight but corroded on the inside. It was still warm outside so truck cranked fine. I found it by hooking a good set of jumper cables to battery and engine. Truck started charging fine. Ohming the cable showed very high resistance between the engine ground and the battery. We had replaced the positive cable when we got the truck but only crimped new ends on the ground cables.

 

Pull alternator and have it checked at a auto electric shop. Load test batteries!

 

Batteries are brand new. It starts right up single digit weather. I doubt thats the problem, but I will keep it in the back of my mind.
Thats a great idea! Im going to try that tomorrow when I get back home.

I can test this with a volt meter correct? 12v on the GP post grounded to the block means its an open circuit to the glow plugs correct?

Will do.

Thanks guys, this is great. I must say I was a little bummed lately seeing that my usual forum has all but died. Everyone went to Facebook. I am very appreciative of this forum and the good knowledge that its members provide.

 

If your batteries are brand new then something took out your old ones. Having your alternator tester by an auto electric shop would be a logical starting point. 13.8 volts is not a proper alternator output!

 

If I am not mistaken 13.8v - 14.2v is in fact the ideal output for an alternator under normal operating conditions when considering a healthy electrical system.

 

14.1 to 14.3. Alternator takes out batteries or bad batteries/battery takes out alternator, are the most common electrical problems. These two power sources should be the starting point for trouble shooting. If the batteries were replaced and or load tested, alternator should be bench checked.

 

I am not receiving the message you are trying to relay.

Are you saying that an alternator must output 14.1v - 14.3v in order to be considered good?

Is that voltage measured at the alternator or the battery terminals?

I agree that a bad battery or a bad alternator can adversely affect the other, but a healthy and conductive system can read 13.8v - 14.2v from what I have experienced and been going by for decades.

Maybe I am wrong though, it happens all the time...

 

The flow chart for diagnosing this problem starts with eliminating the batteries and alternator as the cause. Battery and alternator plugs and connectors can be inspected upon removal, but bench testing should still be preformed by a qualified auto electric shop to guarantee component functionality, even if corrosion or high resistance connections are found.

 

Understood and agree with you that inspection and testing are in order and should be adhered to in order to resolve the issue. Although, my question to you is in regard to you stating "13.8 volts is not a proper alternator output".

My understanding is that in a healthy electrical system (battery, wires, connections, alternator) that 13.8v is in fact an acceptable alternator output. I am not stating what the OP's faulty part or connection is, I am only attempting to understand why you feel 13.8v - 14.2v is not a "proper output" from an alternator.

I have a newish 160A alternator, newish Northstar AGM batteries and newish wires that have been doubled up and I regularly see 13.8v - 14.2v via a multimeter or the in dash voltmeter in the truck or the brake controller which has a voltmeter in the menu. In my opinion and based on my experience if the electrical system is healthy, then 13.8v is a proper alternator output.

Again, maybe I am wrong and when I have been using a multimeter and checking for alternator or battery failure over the past three decades on all of the vehicles I have owned I have been doing it incorrectly. Maybe my electrical system in the 7.3L is not working well... I can tell you that the truck will fire right up after sitting for months on end without a charger hooked up to it though, so something is working right.