Weird charging anomaly?

cbxer55 · Nov 29, 2018

Been noting an odd occurrence on my 98 Ranger. When just putting around, the volt gauge appears normal. When getting into the throttle, at a certain rpm, the volt gauge suddenly drops and, if at night, the lights dim. Last time I was on the highway with it, at around 85 mph, the same occurs. Alternator or voltage regulator? Belt and battery are new as of last year.

Still the factory alternator at almost 160,000 miles. I also use a digital volt gauge that plugs into one of the cigg. lighter outlets. It ranges from 13.6 to 14.2 normally. When the above occurs, it drops down to 12.3 or 12.4 immediately. As soon as the rpm's drop down, voltage returns to the high numbers.

2trux · Nov 30, 2018

When you hit 85 your Ranger probably went catatonic from fear and started to shut down. :woot:

adsm08 · Nov 30, 2018

My Explorer (same alternator) used to do the exact same thing, at almost the same mileage. It was the alternator.

85 MPH means higher RPM. When voltage goes down as RPM goes up it is almost always the alternator not being strong enough to keep up with the increased load.

I once, on an 04ish F-150, saw it be a rubbed wire to the PCM that couldn't carry the command signal well, which is a situation that doesn't apply to a 99 anything.

cbxer55 · Nov 30, 2018

I figured it is the alternator. Just wanted that thought confirmed. It is 20 years old, after all. Amazing it lasted that long. The one in my Lightning needed to be replaced at ten years.

RonD · Nov 30, 2018

Alternator pulley is usually a 3 to 1 ratio with crank pulley
You can check what yours is by dividing Crank pulley diameter by alternator pulley diameter
i.e. 9" crank pulley / 3" alternator pulley = 3, so 3:1 ratio

This means when engine is at 1,000rpms, alternator is at 3,000rpms
When engine is at 4,000rpms, alternator is at 12,000rpms

At higher RPMs an alternator can stop working because of worn parts like bearings or brushes, not all that unusual at the extreme ends of either high or low RPMs(dimming lights at idle)

So I would agree, alternator is the issue.

cbxer55 · Dec 1, 2018

2trux said:
When you hit 85 your Ranger probably went catatonic from fear and started to shut down.

Really? I do 85 and 90 all the time on the freeway, just staying with the flow. But truthfully, my speedo is about 10% optimistic. So at 80, it's really doing 72, etc. In any event, my truck has larger 15 inch rims, wider in the rear, 255/60 tires in the back, 205 on narrower rims in the front. And to boot, Hellwig anti swaybars at both ends. Also put new end links, and all bushings on them in 2015, as they were pretty worn out. It's nice and stable at those speeds. Also has a catback exhaust, MAC cai, and a JET chip. Runs sweet!

But yeah, the 373 gears have it revving pretty high at those speeds as well. Don't have a tach, so don't know that number.

cbxer55 · Dec 2, 2018

Changed the alternator today, problem gone. New alternator has a slightly smaller pulley, but the tensioner was able to handle the difference. I have a digital volt gauge that plugs into one of the cigar lighter outlets, it always reads between 13.8 and 14.2. No change.

2trux · Dec 4, 2018

cbxer55 said:
Really? I do 85 and 90 all the time on the freeway, just staying with the flow. But truthfully, my speedo is about 10% optimistic. So at 80, it's really doing 72, etc. In any event, my truck has larger 15 inch rims, wider in the rear, 255/60 tires in the back, 205 on narrower rims in the front. And to boot, Hellwig anti swaybars at both ends. Also put new end links, and all bushings on them in 2015, as they were pretty worn out. It's nice and stable at those speeds. Also has a catback exhaust, MAC cai, and a JET chip. Runs sweet!

But yeah, the 373 gears have it revving pretty high at those speeds as well. Don't have a tach, so don't know that number.

Just kidding, I have an 89 and I don't think I would want to push it to 85+.

cbxer55 · Dec 7, 2018

Failed to mention that a friend of mine and myself rebuilt the front end in July. New upper and lower control arms with new ball joints with grease fittings. New inner and outer tie rod ends with grease fittings. Feels nice and tight now. At 85 mph it feels nice, no wobble or shimmy as it was doing before the rebuild.

All parts came from NAPA, and are really nice parts. Didn't change the caster and camber at all. Toe was a bit out at first, but it's all good now.

Weird charging anomaly?

cbxer55

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adsm08

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RonD

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