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Lately I’ve been noticing on my 86 IROC that when I start the car (first start of the day) it will start up fine and the battery gauge will read just above thirteen. As I’m driving for a while I’ll start to notice that when I come to a stop the battery volts will drop to 9-10v??? while I’m at a light. At night with the lights on, the dash lights dim a bit when I’m stopped. As soon as I come off the brake and start driving the battery gauge goes back up and the dash lights brighten. This doesn’t happen immediately after I first start driving the car only after I’ve been driving for 10 minutes or so. Could this be my alternator considering that my battery is fairly new??? Another odd thing is when I have my turn signal on both the battery needle and RPM needle start to slightly move up and down until the turn signal is turned off???
With the engine idling and a load on the electrical system (headlights and A/C on), read the voltage across the battery terminals with a digital multimeter. Post the result ITT.
Still sounds like alternator failure as it heats up OR even a bad ground - block to chassis, block to firewall, battery to fender support.
I ran into same problem after I had my alternator rebuilt. Rebuilder repainted the alternator which I later discovered would not ground it
to the engine. I added a ground strap block to chassis & problem solved. Left the alt as is painted.
The alt would charge properly but after an incident of about 30 miles when I stopped for a red light, voltage dropped to about 10V & alt was super hot.
When cooled down it would charge properly.
Yesterday for the heck of it I took my car to AutoZone so they could test the battery and alternator. When he hooked the cables to the battery he said that the battery was fully charged 100% but that the “crank health” of the was bad???
Not if there's 14.x volts across the batt with the engine running, and it went down to high 12s when you turned the engine off. (should be around 14.2 - 14.5 depending on the temperature)
Did that ... got 15 volts.
Not really enough precision. For the moment it's probably OK though, especially if it's a volt or 2 lower with the engine off. Also, it depends on where exactly you put the black lead, and where you put the red lead.
Repeat the measurement, except with more decimal places, as in, 14.4 or whatever. Get the following voltages:
Across the battery terminals, engine running and not running (red lead on batt +, black lead on batt -)
Across the alternator (red on the big post, black on the case, engine running from here on out)
From engine block to chassis (red lead on a screw on the firewall, black lead on engine block)
Batt terminal in fuse box to firewall (red on fuse, black on bare metal under the dash)
Just for the halibut, since you say the voltmeter varies with the blinkers, check those last 2 with the hazard flashers running, and see if they vary up and down
Thanks Sofakingdom. I will try that. It’s crazy because the car fires right up and the gauge stays where it’s supposed to be for a while. Then after about 15 minutes or so of driving I notice that when at a stoplight the volts will drop to about 10??? I’m guessing according to the gauge. As soon as the light changes and I drive off the gauge goes to where it’s supposed to be. I don’t think it’s a parasitic draw??? It just recently started doing this and I haven’t changed any wires etc??? I know the alternator is a bigger than stock one and I’ve never replaced it and it’s been on there since I got the car. That’s why I was thinking it could be the issue?
Besides what mentioned above. Diode trio. Check the back of the alt by the vents. There's three diodes somewhat visible. Might be one of them is burnt out.
I will check that. Thank you. I’m going to do the tests Sofakingdom suggested also when I get time tomorrow. I’m really leaning towards the alternator???
What you are describing is not unusual. Along with the checks that the members have suggested, you should take a close look at the wire that goes from the large stud on the rear of the alternator to the battery. If you have installed a higher output alternator, then the wire should be upgraded to a larger size. The stock wire is barely adequate for a stock alternator. I forget what I installed, but I think it was a 4 gauge. Other folks have installed even larger, but they have huge amps and other stuff. I have one amp in the trunk with a single subwoofer. I do not see my volt gage doing what you described. I did install a ground strap from the motor to the frame. Another one from the rear of motor to the bulkhead.
Thank you for the reply it’s definitely confusing? I’ve had the car for several years and it’s never done that. I’ve changed the battery before but never the alternator. Considering I’ve not done any recent electric repairs I’m leaning towards the alternator being old and needing replacing??? If I had to guess it’s over 6-7 years old at least???
Do you have a digital multimeter? If not it's time to buy one. Put the meter on the battery with the engine off, need 12.6 volts for a fully charged battery. If you've got 12.6 start the car and read the multimeter, should be mid 14's.
Gauge on dash is just a worn out indicator with a 40yo car, it is not a diagnostic tool.
Thanks for the reply I did use a multimeter and got the correct readings. I agree with you in terms of the gauge and would believe that the gauge is off but after driving for a while and noticing the gauge drop below the halfway point I notice my dash lights dim??? This is what’s leading me to believe there might be an issue. Also it’s never done that before and being that the battery is good I’m leaning towards the alternator. Other members have suggested a set of tests I can do with the multimeter which hopefully I will get to today
I did notice something odd yesterday??? When I started the car (cold start) it started right up as usual but I did hear the alternator making an odd noise??? Almost like it was working harder than normal (for lack of better terms). It was louder. At first I thought it was a high idle but I did the thing where you put the screwdriver on it then on your ear and it was definitely coming from the alternator. I turned it off checked the belts and they seemed fine??? I started it back up and the noise was gone??? I did change the belts on there several months ago. Could I have overtightened the belts? Sadly on the 86 there is no tensioner pulley. Also the alternator bracket on my car doesn’t look original it looks like it’s been fabricated. I don’t know if the previous owner did that when they installed the larger alternator?
It’s just odd that on start up and initial drive the voltage is good no issues but then slowly start to drop? Now I’m starting to lean to the belt being the issue considering the symptoms started recently and I changed my belts several months ago? Can the issue I’m describing be indicative of a belt being too tight or a slightly misaligned alternator?
Please disregard the picture threads prior to the pic of my engine bay. Don’t know how they uploaded??? The bottom picture is my alternator and bracket. If you look close to the left of the bracket it looks as if something was cut off it? That is why I assumed it wasn’t a stock bracket???
From: Franklin, KY near Beech Bend Raceway, Corvette Plant and Museum.
Car: 1992 Pontiac Firebird
Engine: 5.0L L03 TBI
Transmission: 700R4
Axle/Gears: 2.73
Re: Alternator/Battery volts
Left click on the picture to highlight it. Press the Delete button on your keyboard to delete it. Rinse and repeat until all the ones you don't want are gone. Save your edit.
That's the stock alt bracket. No telling why it's all fornicated that way. You can grind or file it back down square and paint it.
Can the issue I’m describing be indicative of a belt being too tight or a slightly misaligned alternator?
No.
If the belt was loose it would do the opposite thing; namely, it would slip when the alt loads it heavily, which is recharging right after starting, then slip less as the batt reaches full charge. And we STILL don't know what the voltages are at all those points under all those conditions.
GET THE EFFFFFING VOLTAGE READINGS ALREADY. All of this "maybe it's this maybe it's that could it be this other" is a COMPLETE WASTE of your time and mental effort, not to mention exhausting the patience of those trying to help you. GET THE VOLTAGE READINGS and quit with the fiddle-farting around. If you don't have a multimeter, go get one; it's BY FAR the most useful thing you can have when dealing with electrical issues. All the rest of that CRAP is just that, CRAP. https://www.harborfreight.com/electr...ity-59410.html That one is WWWWWWWAAAAAAAAYYYYYY better than their $8 one.
There's no "the" "battery fuse", as such. However, a couple of them are fed from battery; the STOP/HAZ, TAIL, and CTSY (looks like the printing for that one is gone), which is right next to the FP/INJ2 one.
The 2 batt voltages look fine. I'm inclined to agree w the vendor, the batt itself is probably OK, as is the alt.
The voltage from block to firewall tells how secure the ground between them is. There's a braided strap that goes from the pass side head to the firewall, that grounds the chassis to the block. The block of course is connected to the batt by the neg batt cable (or should be anyway), so there should be very little voltage drop there, probably less than .02V. .06V between the block and firewall seems reasonable.
Were these readings taken while it was in the act of screwing up?
No the voltage was steady. I am going to take it for a ride in a little while to see what it does. Last night when it did act up (voltage was dropping at stoplights) I got it into the garage to run the tests but when I put it in park the gauge went to normal. I will take it for another drive to see what it does and run the tests again
Took the car out after about 15 minutes started doing the whole gauge dropping at stoplights thing. Had the lights on and the dash lights were dimming a bit. Got back to the garage as soon as I put it in park the gauge went back up. Took some readings either way.
Lights on car running-Battery Volts 13.8
Alternator Volts 14.7
Car off Battery Volts 13.05
Its like it’s only doing it while the car is in drive after driving for a while?
Lights on car running-Battery Volts 13.8 Alternator Volts 14.7
There's a problem here. Whether it's "the" problem isn't completely clear, butt it's definitely "a" problem. (ahem: opportunity for a solution... we don't have "problems", do we)
The only thing between the alternator and the battery is a piece of about #10 wire on the + side, and the neg batt cable on the - side. No way there should be almost 1V of voltage drop in that.
Take the neg batt cable off of that bracket and make sure the connection is clean and tight. Do the same where the bracket bolts to the water pump. Inspect the wire going from the alt post to the + batt cable closely; look for signs of heat, corrosion, etc.
After several long days at work I had some time to mess with the IROC. It sat for 6 days but it started right up no issues. Drove it around for 20-25 minutes or so and the issue started. Car drove fine no hesitation or anything but again at stoplights the battery voltage would drop below the halfway point and the dash lights would dim. Got it back in the garage and took some readings which were the same as before. I did inspect the wires/connections and they were clean and tight. (Will upload some pics). I did notice though that the wire leading from the positive cable to the alternator looks like it was tampered with some time in the past??? It does have electrical tape on the end just before the connector that bolts on to the alternator. It’s been like that for as long as I’ve owned the car 4 years???
It'd be worthwhile to know what's under the tape, butt it doesn't look like it's been getting hot. Which if The Problem were there, it would be getting EXTREMELY hot, like, smoking.
So, WHILE IT WAS IN THE ACT OF SCREWING UP, what were the voltages in the list I gave you?
Measuring those WHILE IT'S IN THE ACT OF SCREWING UP is THE ONLY WAY to track down where the voltage drop is, besides stumbling on it by sheer dumb luck.
Will do. It only does it while I’m stopped (after driving for 20 minutes or so and the transmission is in drive). Should I keep it in drive and have someone else take the measurements? Because as soon as I put it in park the battery voltage gauge goes back to normal???
Whatever it takes to get measurements WHILE IT'S IN THE ACT OF SCREWING UP. That's all that matters. Ones taken while it's working right, tell all about what it's doing when it's working right. (duh) Butt they don't tell what it was doing WHILE IT'S IN THE ACT OF SCREWING UP.
Working on intermittent problems like this is not fun. I totally get that. Butt, there's really no alternative: gotta catch it in the act. Reminds me of people who complain that their car stumbles and sputters and "bogs down" and whatnot when they're on the highway trying to accelerate, which is clearly a fuel pressure / delivery problem; we tell them to get a fuel pressure reading WHILE IT'S IN THE ACT OF SCREWING UP; and instead they tell us what the FP is when it's sitting in the driveway idling smoothly and happily. Doesn't help. A clogged fuel filter, a weak pump, or whatever, can allow adequate fuel to get through when the engine's demand is at a minimum, butt cause it to fall flat on its face when more fuel is required and it can't deliver. In that case, they need to tape their FP gauge to the windshield, and have their assistant watch it as they drive it and MAKE IT SCREW UP. Yours unfortunately isn't quite that easy; you can't exactly somehow make it screw up at will, or under particular conditions, or whatever; butt that still doesn't give us the ability to tell how it screws up, from observations made while it's not screwing up.
Being that the symptoms which are; the battery gauge drops and the dash lights dim only after driving for 15 to 20 minutes and I come to a stop in drive. I will have someone keep it in drive while I take the measurements and report.
This sounds like a classic case of undersized charging system at low idle speed.
If vehicle electrical loads exceed alternator output current, then system voltage immediately drops to battery OCV (12.6V) or less. This is why your voltage is stair stepping with rpm. Apparently your alternator cannot keep up at somewhere between 700 - 600 rpm engine speed. You just need to run the alternator a little faster at low idle so that it can make more current. You can either install a smaller pulley on the alternator, or bump up idle speed a bit.
It is normal that alternator output current is higher just after a cold start-up than it is warmed up. It can take up to 20 minutes for the alternator to heat up and become "temperature stabilized", and the output might swing down as much as 10% in this time period. Electrical loads also vary depending what is operating at the time. Get the right combination of electrical stuff drawing loads at the same time, with the alternator at a very low speed, and boom.... it exceeds alternator output and system voltage suddenly drops to 12.6V or less.
Thank you so much for the detailed response. I assumed that my alternator and battery were good??? Being that the car starts up every time and drives with no issues. I did check the timing the other day and it was a little bit less than the factory 6 degrees. I just found this odd that this all started shortly after I replaced my belts several months ago. I was thinking that I either tightened them too much or not enough. But Sofakingdom stated that chances are this was not the issue. I will post the readings I get with the car in drive just to verify and eliminate any other possiblities. Thank you again for the detailed response.
You can take two simple voltage measurements to figure out whether you have excessive voltage drop in your charging system between alternator and battery.
With engine running at the same conditions,
1) Voltage between battery B+ and B- post with engine running.
2) Voltage between alternator B+ post and alternator case.
The difference between these two values is your voltage losses in the charging circuit. It's fine as long as it's not more than 0.5V difference.
That doesn't necessarily mean you don't have a problem somewhere else.... but it does mean your basic charging system cabling and connections is fine.
Also, a battery that just came off charge will hold a surface charge that elevates the voltage reading falsely high. If you're going to take a battery voltage reading with engine 'off', then first bleed off the surface charge by turning on the lights for 10 - 20 seconds. This will help you get a realistic voltage reading from battery at no load (OCV).
