Voltage fluctuations at idle.

[KYEdge]

Ok I'm starting a new thread about this because I don't think this is related to the oil gauge flicker.

I'm having trouble with voltage fluctuations in my Ranger. I have checked with a DMM and the fluctuations seem to range between less than .5V and right around 1V. At idle, or when the RPMs are hovering around 1K (say when creeping along in traffic), you can literally watch the charge needle move up and down. All of the lights (dome, dash, headlights, and taillights) also get brighter and dimmer as this happens.

The truck seems to run rougher as this is happening, but has not actually stalled or tripped an error code.

There is also a slight surge when you initially give the truck throttle from idle that causes all of the lights to get brighter. Once the RPMs are up the truck runs smoothly and the voltage remains steady.

The alternator has been tested, and appeared to be ok but it was an Autozone test. What am I missing here?

 

[DCarey515]

battery

 

[Earl43P]

Neighbor's Taurus was just doing the same thing, but also "at speed" when ac kicked on it would "run crappy". An alternator fixed it.

I had put the Scangage II on that one and watched the volts vary, much like yours. My initial thought was loose belt / bad tensioner, though he did put a new belt on it.

You could really see his voltage flux with an analog meter (sweeping needle). You could turn on the high beams and it would drop a full volt and try to "recover" but even revving the engine wouldn't get it over 13v. Most times, it was just over 12.

So, you should rule out a loose belt and bad tensioner, any bad cables and end up replacing the alternator would be my best guess.

A lot of times, the alternator will fail at higher rpm, lighting the light. Usually that's bad brushes. You "could" replace the VR and brush block assembly on yours if money is tight and you can't afford a new alternator. Some places still stock alternator parts.

I'm going to guess you have flickering oil pressure at idle? Get the voltage problem fixed and your idle should improve. That may be enough to fix the oil pressure too, if your idle rpm is too low from low voltage.

 

[KYEdge]

What is a good way to test an alternator, if there is one? Like I said I had autozone do one of their tests, and they said it was good, but I dunno how much I trust it. I'd hate to drop the money without knowing for sure.

I guess I could replace the battery cables and give that try, they look good, but who knows.

I don't think it could be the tensioner, because I had a new one put on a few months ago and while it was never this bad I had a few of the symptoms before that.

 

[JP02XLT]

Also check the ground connections, at the battery, just behind the drivers headlight & from the motor to the frame, These are well known bad ground spots & can cause your symptoms.

JP02XLT

 

[KYEdge]

Ok, looking over all the ones I can find, all of my ground connectors have this kind of brass looking finish to them. At first I thought it was tarnish, but they all look almost identical. Is this some coating they are supposed to have?

 

[Rearanger]

The alternator has been tested, and appeared to be ok but it was an Autozone test. What am I missing here?

Your first mistake was trusting the parts guys at Autozone, or any other parts chain. As suggested cleaning grounds and battery/alt connections is a good start. It could be the voltage regulator in the alt.

 

[KYEdge]

I've cleaned up the main grounds, and even tried a new battery, and its still doing it. So I guess it has to be the alternator.

 

[wahl_7s]

ok you never said what the alt.is putting out should 13.8 to 14. and if memory serves that gauge is a battery gauge not an alt. gauge. is it the OG battery?

 

[KYEdge]

I'll have to go out with my meter sometime and check what the alternator is putting out. I tested it a while back but I don't remember what it was.

What do you mean by OG battery?

 

[JP02XLT]

You can get a really accurate gage of the system voltage from voltage readings from the cigarette or power port. Like was mentioned you should see 13.8 to 14.2 volts. Test with everything off & then turn one on at time if you see a drastic drop start looking at the grounds for that specific application.

JP02XLT

 

[wahl_7s]

I'll have to go out with my meter sometime and check what the alternator is putting out. I tested it a while back but I don't remember what it was.

What do you mean by OG battery?

original motorcraft

 

[dernst]

Using unknown terms like OG can get confused with other things like Optima Gel battery.

 

[KYEdge]

No it is a replacement battery.

I noticed something tonight by accident. I was in the driveway with the truck running and the dome light on and I accidentally hit the turn signal. The dome light pulsed opposite to the turn signal. When the signal was on the dome light was dim and when the signal was off the dome light was brighter. It did the same thing with the four ways. I turned the truck off and put the four ways on and the dome light stayed steady.

If there was a bad ground or connection then it would pulse running off the battery just like when running off the alternator wouldn't it? I'm leaning more and more on this being the alternator... which would mean four bad ones from two different places. If I have time I'm going to out tomorrow when its light and check the alternators output.

 

[Ranger Kip]

could it (by chance) be the fact that the truck is pulling more electricity as the truck speeds up? being a relay failure? (I think I am correct by saying relay, I might be wrong though).