corvettebob1

I have a 98 that's got heads and cam + blower this winter I had the PCM upgraded to a 2002 since this time I have noticed this when the underhood temps get hot.
It seems the alternator shuts down until the temps go down, this has happened several times this summer when it's been above 90* ambient.
Just wondering if this is normal?
BTW, it's a stock 98 alternator battery voltage drops to less then 13V but returns to normal when I get moving down the road and coolent temps get down from +220* to ~200*

corvettebob1

Anyone?

lucky131969

The only protection I'm aware of, is the fusible links, which lie within the wiring, not in the alternator itself. I would be inspecting the wiring at the connectors and starter. That being said, with enough temperature increase, a solder joint could open in the alternator. If you want a quick test, hook a 10 gauge jumper up to the alternator, and to the positive post of the battery. This will tell you in short order if the wiring in between is suspect.

corvettebob1

Thanks, that's kind of what I thought. I guess it's just a coincidence that it started after the PCM change.

lucky131969

Hard telling. Any codes?

corvettebob1

P0102 HC this is because of a SD tune and the MAF is eliminated.
U1096H BCM
U1096H radio
U1096H HVAC
U1064H A0 LDCM
U1064H A1 RDCM
U1096H B0 RFA
Also replaced the battery about 3 months ago W/Delco professional the old one was 6 years old on a 3 year Delco battery.

lucky131969

With all those loss of communication codes, I think it would be worth examining the ignition switch contacts. Bill Curlee has an excellent thread on it.

corvettebob1

Yes I have thought about that also, however I did replace the ignition switch a few years ago during another witch hunt.
I cleared the codes and took the car for a quick 2 mile drive and this is what come back.
3 codes
U1096H
1064H
1016H All for BO-RFA
These codes seem to be resident ever since the PCM switch when I mentioned this to them they didn't seem concerned.

lucky131969

Ok, well I guess it's up to you....to do some investigation. Inspect wiring between the alternator and battery(to include starter), check the resistance of said wiring, try the 10 gauge jumper, and possibly inspect the ignition switch.

corvettebob1

Well I guess great minds do think alike, I just checked the wiring and it looks good.
Then I checked voltage with a DVM & the car off @ the alternator and then at the battery and it was within .01 volts.
So it's on to other things next I will check fuses for voltage with the key on vs battery voltage, should be the same this should eliminate the ignition switch.

TGstring

the fact that you're stuck in traffic, it's hot, and your voltage drops to below 13V on your Instrument Panel is NOT a problem. For me, at least, it's normal...and that was with an alternator that tested a-ok and a brand new 750CCA battery. I have a 4 guage wire directly connected from my alternator to my battery and have upgraded all my grounds with heavier wire.
I know there are no wiring or ground issues. I have about a .4 to .5V differentiation between voltage measure at the battery posts and my instrument panel. Even if my IP show 12.3V while I'm stuck in traffic, ac pumping, stereo on and on the brakes, I'm not worried because although the battery isn't charging, it's not discharging.

I wouldn't worry about it...

00Corvette

ditto

the car will never be @ it's fullest charging capability @ idle..once you're at 2-3000 rpm or so..that's when the alternator is putting out it's full amperage.
Spend an hour above 2000-2500 rpm every so often for a good charge is all that's needed on a DD type car.

some guys prefer the 100-200 dollar batter "tenders"...the alternator works fine for me.

I'm no electrical expert but the car doesn't use the battery for anything except to crank the starter over and for security features I believe while the car is sitting. Your battery will also charge itself up after sitting overnight just a little bit but it does. Once the car is running, you've got something like 150 AMPS to run all 12V electrical accessories . Each item, headlights 10 amps, ac 10 amps, big stereo 25 amps...and so on.

But this all runs off the alternator..nothing even uses the battery. So, if your alternator/battery check out good on the machine and the car starts every morning..I wouldn't worry about it.

00Corvette

and it has NOTHING to do with the temperature. (unless you have a faulty alternator)

You're purely adding RPM to the engine and spinning the alternator faster...coincidentally would be my bet that your car "cools down" at the same time. Try it before your car warms up and I'll bet it's the same on the charging.

when you buy a good alternator, it comes with a little card inside that shows the amp output @ idle and 3000 rpm I believe..

You just gotta drive it a little more is all

edit: You probably did an underdrive pulley also when you did the heads/cam I'll bet?

corvettebob1

No underdrive pulley, remember it's also blown.
The problem is it shows higher voltage until the under hood temps get high with over a 90* ambient.
Once it cools off the charging or voltage goes back up, if I put it in netural and rev the engine it does nothing to bring the voltage back up.
BTW, I just did my voltage check with the key on and it stays the same at switched fuses.
So I'm thinking it may be the alternator or the fact that the PCM is looking for a higher amp alternator like the later models had remember mine is a 1998 with a 2002 PCM.

00Corvette

where's the embarrassed smilie:o...to be honest I replied to your post w/o reading the thread just off of the title and a couple recent replies. my bad

it is weird that the voltage does not increase at all when it's warm and you bring the RPMs up..it should.

I am not aware of the alternator differences other than mine is a 2000 and I know the thing is expensive and to hang on to the original.

The 98-02 difference maybe the issue but best leave this one to someone who knows for sure. You could probably search out the differences between the alternator functions in the PCM between the two years on here as I'm sure it's been discussed or someone has swapped one before??

Goody

I would think that both fans are on at the high temp time and then the car cools down at which time the aux fan shuts down and thus the volts go up a bit because the draw isn't as much.

Are you running larger injectors, another fuel pump and now putting out more heat thus relying on the fans more? What is the amp draw your car is needing compared to the amp output of the alternator?

Before you go buying a newer alternator I would post this in the FI section and see what others are experiencing with a similar setup.

You could also test the heat theory out buy getting the car to the hot situation and then cooling the alternator down using an external cooling source - a crazy idea would be to use an aluminum foil tray and try to form it to the upper portion of the alternator and then get a small bag of ice and lay it in there carefully so you don't get it caught in the belts or get water into the alternator -- I did say crazy right

Also I don't know if the alternator has a thermal protection feature or if it just gets too hot and something internal shuts down.

lucky131969

Good idea. Perhaps someone with an FI setup might have some suggestions.

lionelhutz

What are your temperature settings for the low and high fans?

I would also suspect that the high fan speed kicks in and combined with the low rpm causes the voltage to drop.

At 13V output your alternator must be doing something because the battery itself would not hold at that much voltage. Battery itself I'd expect to drop quickly to around 12.5V or maybe even lower.

FYI, when I idle my car a bunch and the temps go up and the voltage drops it does not show any voltage increase just by revving it a bit. I have to start driving at say 1000+ rpm for a bit (maybe 8 to 10 blocks) before the voltage begins to show much more than a 0.1 or 0.2 volt increase.

Peter