What in the ....?????? Low voltage reading, yet full battery and alternator working.

Topic: What in the ....?????? Low voltage reading, yet full battery and alternator working. (Read 19593 times) previous topic - next topic

What in the ....?????? Low voltage reading, yet full battery and alternator working.

June 13, 2014, 10:37:03 AM

The curse continues.....

OK here's what you need to know: '87 Cougar 5.0 full digi dash. Battery is 4 months old. Alternator is about 4 or 5 years old and has about 12,000 miles on it. It's a stock output, stock style replacement. No alarm or extra stereo equipment.

Historically since I've owned the vehicle, the voltage gauge has always read a steady 4 bars. Upon leaving for Carlisle last week on Thursday, I pulled the Cougar into the garage where it remained while I was gone with the Mustang. Upon pulling it out Sunday night to put the Mustang away, the voltage gauge shows 3 bars and the chime goes off every 70 seconds (yes, I timed it). The battery icon next to it constantly flashes as well.

I thought perhaps the ignition might not have been fully seated in the off position as I can remove the ignition key in pretty much any position to include when the car is running. I figured I'd drive it around a bit to see what happens and hopefully what happened WAS in fact what I thought and that the battery would just recharge.

I've driven the car a few times since to include 2 highway trips of 15 miles. I've taken note that a combination of braking while having the turn signal on will in fact make the gauge read 2 bars. It will pop right back up to 3 when I remove either one of those two variables.....The car starts up and runs trouble free and I can turn EVERYTHING on and leave it at idle. I did this for about an hour with zero effect. Yesterday I pulled the battery out and put a 40 amp charge on it for an hour. I put it back in the car afterward. No difference.

My voltmeter is BURIED right now and between all the other shiznit that's happened since I've returned, I have had ZERO time to dig it out (shag you 1 year old Samsung washing machine, you suck).

If this were a draw I would expect that the battery would have died or I see some diminished effect by this point. Nothing. Obviously I have to dig out my meter and check the voltage on the battery and while running to see if in fact the alternator is giving me full output. My gut tells me it is though from when the gauge goes from 3 bars down to 2 and then promptly back up. If in fact I am correct, what other glaring thing(s) should I look at first?

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #1 – June 13, 2014, 11:05:32 AM

IIRC there's something to do with a shunt…maybe that's the low oil pressure thing but it may also be for the voltmeter.

http://www.foxtbirdcougarforums.com/showthread.php?10562-beeping-fron-digi-dash!!!!-help!!!!&highlight=digital+beep

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #2 – June 13, 2014, 11:20:35 AM

Yeah, that's for the oil pressure. Mine's reading good. That one seems to be for when the gauge is lighting up the top and the bottom. Mine just reads lower than normal and chimes.....

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #3 – June 13, 2014, 12:07:32 PM

It's got to be something in the dash itself. I have a full digital dash and the voltage gauge always has read 5 bars. It will go down to 4 bars at idle with the A/C, headlamps, and stereo on (all stock) only. Turn any one of the previous items off and it goes back to 5 bars at idle. For what it's worth the car idles at 700rpm hot in park, 625 in drive.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #4 – June 13, 2014, 12:31:23 PM

My 87 bird was giving me weird low battery things on long trips, around town it was fine. stock alt and 200watt no name cd player. everything else is stock.

when i was working on pulling the engine, the two 10 guage wires broke off at the splice i put in that eas included with the new alt connector. i crimped, soldered and heat shrunk over the wires. alt is only maybe a year old.

the stock wiring is way underdone even for the stock alt. throw a 3g in if you find any problems with the alt or your wiring. a partial or bad connection will cause bad readings.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #5 – June 13, 2014, 12:41:03 PM

Bad ground?

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #6 – June 13, 2014, 02:52:27 PM

Dug out my multimeter......

Battery voltage with vehicle off: 12.20

Voltage with engine running: 11.95

I repeated the tests 3 times. Same results down to the hundredth of a volt.

Idle RPM is a steady 750. Any lower and the camshaft I run gets grumpy.

My grounds in the car appear well. Guess I'll bring it for a load test on the alternator.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #7 – June 13, 2014, 03:06:41 PM

i've seen alternators go bad and have a break in the wiring for one of the phases. it can produce kinda funny tests like that. two of the three is enough to kinda keep it running, but not really charge the battery or run many electronics.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #8 – June 13, 2014, 03:08:29 PM

Alt is either junk, or wiring is starting to melt.

as long as a resistance check for negetive battery cable to block isn't too high, id swap in a 3g and call it a day. i wonder if your voltagrle would come up any if you reved it higher.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #9 – June 13, 2014, 08:32:11 PM

Convert to a 3G Your alternator went south.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #10 – June 14, 2014, 12:25:15 AM

Running, the car should be charging somewhere between 13 and 14.4 volts.
I'll have to meter my battery tender tomorrow, see what that "holds" a stored battery at. I think it's similar, just a very low current.
Based on battery's internal resistance if I am not mistaken. Charging "systems" on lawn tractors effectively keep their batteries charged. Very crude and simple system there. Not that with integrated circuits and software you couldn't do *better*.

For this reason the digital dash is awesome, if for nothing else. I was rounding an on-ramp in the red car last month and suddenly heard a beeeeep and noticed it switched to oil pressure. I immediately went into a panic mode, but at the same time noticed that the normal number of bars (3 or 4 I think?) were present. Toggled through elec/temp/oil again, no change. Pulled over anyway, shut 'er down. Not full but not real low either. Must have momentarily sloshed from the pickup. You always tell yourself you'll keep an eye on the gauges, but you almost never hear that unique beep, so when you do its an "attention-getter"! (say that in a Jackie Gleason southern voice

)

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #11 – June 14, 2014, 09:18:48 AM

3g, all the way. No better time than now. Before I did mine, I couldn't stay above 13.5v with the headlights, rear defrost and eatc on. After, I stay between 14.3 and 14.6 no matter what's on. I even installed a overrunning one way clutched pulley on it (eliminates belt slap on hard upshifts).

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #12 – June 14, 2014, 09:53:53 AM

You may want to make a couple of quick checks with your volt meter to confirm the alternator is probably bad.
The voltage checks will be on the alternator connectors. You can unplug them if that is easier for the probe type you have.
1. With the key off, check for battery voltage on the BK/O wires to the Alt B+ . Look for overheating damage to this connector.
2. With the key off, check for battery voltage on the Y/W wire to the regulator A terminal.
3. With the key in run (don't start) check for battery voltage on the LG/R (may be LG/Y) wire to the regulator I terminal.

You need all of the above voltages for the Alt work.

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #13 – June 14, 2014, 11:33:35 AM

Since your car has an external voltage regulator so you might want to grab that and take it to get checked along with your alt. Just because the alt is somewhat new does not mean its good to go. We have all been down that road a couple of times.

If its the alt then hopefully its still under warranty and if it is the regulator then that is cheap enough. I too would suggest going to the 3G alt but if you are 100% stock then I don't know if it is worth it. I have waaay too much aftermarket electrical components on both of my cars so I made the swap to a 3G years ago.

Darren

What in the ....?????? Low voltage reading, yet full battery and alternator working.

Reply #14 – June 14, 2014, 02:22:24 PM

Quote from: Aerocoupe;434824

Since your car has an external voltage regulator so you might want to grab that and take it to get checked along with your alt. Just because the alt is somewhat new does not mean its good to go. We have all been down that road a couple of times.

If its the alt then hopefully its still under warranty and if it is the regulator then that is cheap enough. I too would suggest going to the 3G alt but if you are 100% stock then I don't know if it is worth it. I have waaay too much aftermarket electrical components on both of my cars so I made the swap to a 3G years ago.

Darren

He says it's an 87. That should be a 2G with internal regulator.
The voltage I gave for the LG/R wire to the I terminal is with the connector unplugged. Also if the Alternator warning light is on with the KOEO , this circuit is good.