Need a Charging Sys Expert - I've got a "twitchy" Amp guage ... sometimes.

[cobrajocky]

I have a 97 Mazda B-4000 SE 4.0L V6 2x4, everyone knows it's the same as a Ford Ranger XLT Extra-cab just with a very slight difference in "box wrapping". I've had a lot of trucks, but this puppy is always surprising me with something new gone-wrong or warning. just recently maybe a couple months after installing a complete new AC system in June (compressor, all the hoses, evap, etc) under the hood (I'm only referencing this "in case" there is some remote connection) once in a great while the Battery warning indicator sputters (flickers), never stay on, goes off while accelerating or cruising and may never come on again for days, a week. However, the battery gauge "twitches", like a nervous finger the tiniest amount while idling at a stoplight or stopped traffic and goes steady when accelerating or cruising.

Two years ago I replaced the Alternator because it flat died, and I never got any of these odd indications before that crapped out, it just died suddenly. I replaced it with an after-market, can't remember if it was a Korean or Commie Chinese made unit, but I didn't buy the cheapest one either.

I put a VOM on the battery and had the wife rev the engine (not her) to about 2500 RPM and I get 13.4 to 14 Volts at the battery terminals.

What is going on?
Thanks, experts.

 

[Curious Hound]

What is the voltage when idling? Immediately after startup, it should be around 14 volts, maybe a tiny bit higher. After 3 minutes or so, it should go down to about 13.5 roughly. What is your battery voltage after the truck sits overnight? How old is the battery?

 

[adsm08]

Also, at idle, what is the AC voltage reading at the battery terminals?

 

[cobrajocky]

What is the voltage when idling? Immediately after startup, it should be around 14 volts, maybe a tiny bit higher. After 3 minutes or so, it should go down to about 13.5 roughly. What is your battery voltage after the truck sits overnight? How old is the battery?

OK, took VOM measurements this morning, sorry been out of town a couple days.

Battery voltage cold over-night, unused for about 4 days, nights getting down to 50 degrees. - 12.5 VDC

Terminal /Battery voltage immediately after starting - peaks at 14.6 V, drops to 14.5 V after a minute on "warmup high RPMs"

Terminal voltage rev to 2,500 RPM - stays at 14.5 V

Terminal voltage at idle (900 RPM) - 14.5 V, never drops for the 5 minutes I tested.

Battery voltage / engine off - 12.8 to 13 VDC

The battery is less than two years old, Walmart "Max EverStart" group 65 rated at 650 CCA, nowhere near their cheapest.

I don't use this truck that often, maybe a couple times a week, less than 30 miles. A 1997 B-4000 (4.0L V6) only has 98k miles!

 

[4x4junkie]

^^^

All of that looks completely normal (the alternator is temperature-compensated to optimize charging of the battery). The voltage actually can rise over 15V right after startup on a cold morning if it's cold enough. It should never drop below 14.1 V or so after full warm-up (14.4 being typical on a comfortable day).

I suspect you might have something intermittent going on... I would suggest maybe wire up a multi-meter to a cigarette lighter plug and plug it into the lighter socket and monitor the voltage as you drive. Next time you see the truck's gauge twitching or whatever it's doing, see if the same is reflected on your voltmeter. If it is, then you'll need to go over your wiring looking for loose connections in the area you might've been working on it (wiggle the wiring while you have someone watch the gauge, for example).

 

[RonD]

Walmart sells a cigarette lighter volt meter for under $15

Not a bad idea to see if dash voltage is the issue

 

[Curious Hound]

Those are some good ideas. An analog meter (the kind with a needle moving across a scale) will give a better indication of quick voltage transients. The needle is more sensitive than most digital meters. The problem could be confined to the gauge cluster or interior wiring as alluded to above. This is starting to sound like a loose connection somewhere.

 

[cobrajocky]

4x4junkie

Thanks for the analysis, it's been VERY intermittent, of course using the truck has been too. Wiring a VOM with leads long enough to get to the "cockpit" will be a tough proposition. I'll check into RonD's idea of a cig lighter meter if I can find one that's digital as an analog would be too vague.

Since it does also flash the battery warning light (that flickers too) sometimes when this happens, would that throw a code that I could read with a code reader?

 

[RonD]

No, the charging system is not monitored by the computer

If battery light flickers at the same time then your alternator is most likely starting to go

If it happens more at idle, lower RPMs, then you are losing one of the 3 Fields in the alternator

It could be a loose connector on alternator, easy to check that, only 1 wire on a stud and one 3 wire connector, check for corrosion

On the inner fender is a "starter relay", the smaller battery positive cable connects to this, check and clean connections, ALL POWER for the vehicle passes thru this connection

 

[PetroleumJunkie412]

Also, at idle, what is the AC voltage reading at the battery terminals?

No, the charging system is not monitored by the computer

If battery light flickers at the same time then your alternator is most likely starting to go

If it happens more at idle, lower RPMs, then you are losing one of the 3 Fields in the alternator

It could be a loose connector on alternator, easy to check that, only 1 wire on a stud and one 3 wire connector, check for corrosion

On the inner fender is a "starter relay", the smaller battery positive cable connects to this, check and clean connections, ALL POWER for the vehicle passes thru this connection

These two, FTW.

 

[alwaysFlOoReD]

What does the a.c. voltage check tell you? How much should I see on a good alternator? Is there a range that is ok?

 

[PetroleumJunkie412]

Checking rectifier.

Alternator Ripple Voltage Testing

Before computers and networks in vehicles, an alternator that was producing AC voltage or ripple through the electrical system would cause flickering lights and maybe an ignition problem. Today, excessive ripple voltage can cause communication issues with networks and communication DTCs in...

www.underhoodservice.com

 

[cobrajocky]

No, the charging system is not monitored by the computer
If battery light flickers at the same time then your alternator is most likely starting to go
If it happens more at idle, lower RPMs, then you are losing one of the 3 Fields in the alternator
It could be a loose connector on alternator, easy to check that, only 1 wire on a stud and one 3 wire connector, check for corrosion
On the inner fender is a "starter relay", the smaller battery positive cable connects to this, check and clean connections, ALL POWER for the vehicle passes thru this connection

I have doubts that it's the Alternator going south, while it's the original (remember it's only 98k miles old and I understand these had great service records into the 150k + miles range) and the output is just too stabile; it maybe something like a bad or loose connection. I did do a complete under the hood AC replacement, everything but the condenser - the hoses literally rotted away and leaked/seized compressor.

So maybe I knocked something lose. It does seem to coincide with the AC replacement. Will look for that first with your suggestions. Thanks! If it weren't so inconsistently sporadic, it would be easier to diagnose, this is the worst scenario.

BTW, Walmart doesn't have any Cig Plug volt gauges, "out of stock". Did a general Google search, didn't see any analog needle types at all, everything is digital. Ordered one from a CA EBay seller for under $6, won't have it until late next week. I may jury-rig one of my old cheap VOM's to a spare Cig Plug adapter and put the meter on while I drive it next.

If anyone thinks of something else to check or has experienced this sporadic twitchy battery gauge and battery light, please add your 2-cents.

Thanks all!

 

[cobrajocky]

Hey guys, here's an update -
Checked all the connections at the Alternator and everything is well seated and nothing loose.

The cig lighter socket Voltage meter showed up and I have been using it for the last 5 days, taking readings under different circumstances. As you may know, the late 90's Mazda B-4000 / Ranger XLT's have an aux socket on the dash that is NOT a cig lighter socket, I used that.

Battery cold with the ignition on - 12.6 to 12.8 VDC
On startup from cold after a few days sitting the meter reads 14.3 to spikes of 15.8V during which the Battery indicator light is flashing (flickering to flashing rhythmically), not steady on.

When idle drops after about 5 minutes - meter reads 13.5 to 13.8V

While driving on the open road or freeway - meter reads 13.3 to 14.1 on hard accelerations.

I've never seen the meter in that socket drop below 13.1 V once the motor is warmed up and driving slow or moderate. Most of the time the Battery warning light does NOT come on, or even flicker.

Similarly, the charging /battery gauge ONLY twitches while idling at a stop, never while driving.
The battery is a 5 year and only less than 3 years old, one of Walmart premium models, higher CCR than factory spec.

I am still at a loss as to what is going on!

 

[RonD]

Alternator should NEVER go above 14.9volts, higher than 15volts will ruin a 12volt battery, hence the flashing light

Engine running it should NEVER go below 13.5volts, hence the jumping gauge

So you have a voltage regulator issue, regardless of its age, actually I would replace the whole alternator, bad diode on a Field could cause the 15+ volts