Ok I have a 01 5.9l Magnum. A few days ago it wouldn't start and sounded like it was a dying battery. If it did start as soon as I let off the gas it went dead. Tried to jump it off but that was not the problem because it did the exact same thing even while hooked up to be jumped off. I took the battery and had it tested the battery is a good battery and when I was putting it back on I made sure to clean the terminals in the post and all that so when I went to crank it again it started right up and was doing fine. Fast forward to yesterday afternoon it started up just fine but about a block down the road The check gauges light came on and my battery gauge flew up to past the 18 like it went to where it couldn't go any further. I got it home and disconnected the battery and I'm trying to figure out what exactly is going on. Back in July or August last year I replaced the alternator the starter and the battery so I'm not real sure I was thinking voltage regulator but I'm not even sure where to find it on this truck. Question is is it probably the voltage regulator has gone out? Is there another issue it sounds like that I have no idea what? Please someone help.

 

Possibly the voltage regulator but the typical failure mode is that the alternator stops charging, not going max output. Check all the grounds between the engine and battery as well as the grounds for the PCM. Also the power connections at the alternator and starter.

 

So if you had to throw out a guess you wouldn't say voltage regulator? Side note, where in the world is it on the 2nd gens? I thought it would be with the alternator but I can't seem to find it. I don't mean to sound ignorant or like I don't know anything about what I'm doing I just honestly am stumped on this one.

 

Voltage regulator is part of the PCM..... Which makes it expensive. A cheaper alternative is to convert to an external, old style voltage regulator.....

 

I was looking at those this morning. I know it's not possible to get a definite answer without someone being able to look at it but is the voltage regulator at least me going in the right direction? Or is there another direction that I should go first? I do appreciate you all taking time to respond to me thanks a lot. There's no way that I can replace a PCM right now but I think I could probably swing the external regulator.

 

Actually I'm still very much blown away at how the voltage regulator is inside the PCM. Is it normal for that to be that way?

 

That was someones brilliant idea, and personally, I think they should be keel-hauled for even suggesting it.... "Hey, I know, let's put a part the fails fairly often, inside a significantly more expensive part, that doesn't. We can make more money on parts sales that way."

 

Okay so I went out to check all the connections and everything seemed okay so I started the truck and I let it run for probably 5 or 10 minutes and the battery gauge is fine it's running fine there doesn't seem to be any kind of a problem now. Could a bad voltage regulator do it intermittently?

 

Yup. Sure could, be, a rubbed thru wire could as well..... We having fun yet?

 

To be fair, pretty much anything built in the last 30-ish years uses pulse width modulation from the PCM to control alternator output. It allows for much tighter voltage control compared to the older electromechanical regulators, which benefits the electronic modules. Now whoever came up with the idea to move heater core and evaporator inside so you need to pull the dash to fix anything deserves keel-hauling ....