`96 Firebird Engine Codes - does bad alt show up?

[TGregg]

Having a bizzare electical problems with my 96 Firebird 5.7L/350CI. I can write up the details later (it'll take a while) but have a quick and easy question first. I took it in to AutoZone for the free test, and the guy plugged a handheld into the dash to read the engine codes. It was fine, no error codes.

My question is this, would the car computer know if the alternator was bad?

The alternator only has a single wire that runs straight to the positive battery post. AFAIK, there are no sensors or inputs or anything of that nature to the computer.

TIA.

[Trash man]

the comp wouldnt kno but u might get a battery light or u can tell by ur headlights if they are very dim when running most likey the alt is bad. but get a dvom and set it to volts and measure the volts when running. should be between 13.(?) and 15.5 volts

[TGregg]

the comp wouldnt kno but u might get a battery light or u can tell by ur headlights if they are very dim when running most likey the alt is bad. but get a dvom and set it to volts and measure the volts when running. should be between 13.(?) and 15.5 volts

Hmmm, then my alternator must be OK, cuz I have a voltage gauge on my dash that reads between 13 and 15.5. Thanks 88bird5spd.

[Christopherrr]

easy way to check your alternator is going bad or not is simple. Start car, turn on all assessories, ie lights, fans, radio. Then unplug the negative terminal on the battery. If the alternator is good, then the car shouldn't die...if it does, then it's going bad.

Credit goes to Jeff95Z28

[TGregg]

Thanks Chris, and Jeff95Z28 whoever you are. I'll give that idea a shot. Meanwhile, anybody know where I can find the bleeder screw(s) for the cooling system on my 96 firebird 5.8L? I replaced the overflow tank, and I'm sure there's air in the system.

[fastTa]

Meanwhile, anybody know where I can find the bleeder screw(s) for the cooling system on my 96 firebird 5.8L? I replaced the overflow tank, and I'm sure there's air in the system.

Props to Shoebox for the pic:

[TGregg]

Sweet! Thanks Kevin, and Shoebox.

[Injuneer]

The PCM does know in OBD-II:

P0562 = System Voltage Low
P0563 = System Voltage High

[TGregg]

The PCM does know in OBD-II:

P0562 = System Voltage Low
P0563 = System Voltage High

Thanks Injuneer.

[TGregg]

OK, so I tried the disconnect the battery idea. I started the car, then disconnected the negative cable from the battery post. At first, everything seemed to work well. Then my passenger window wouldn't go up or down. It didn't matter if I had headlights/radio/ac on or not, it just wouldn't budge. My headlight motors worked intermittently. Then my driver side window was frozen, but the passenger side worked fine.

Then when I kicked on the AC, the engine would miss a couple cycles.

My voltage gauge was normal, about 14 volts or so.

Also, I noticed something under the hood was making a whining sound, a lot like I imagine a pump that isn't pumping anything might make. It seemed to come from just right (driver's side) of center of the engine near the back, around this big black plastic box.

I wonder if something could be drawing a lot of extra power.

[Injuneer]

Is it possible the noise was coming from the front of the engine, just below the driver's side head? The AIR pump runs for about 2 minutes at startup, and it is electric, and they do draw excessive current when they start to rust and sieze up.

Does your car have traction control? That sounds like what you call the "big black plastic box". That shouldn't be operating when the car is just sitting at idle.

If you had 14V on the dash, appears you may have a problem with engine and PCM grounds. If they aren't good, they screw up the sensor readings, PCM, ignition, ABS and traction control, etc.

[TGregg]

Yeah it has traction control And that could well be what the box is, there's text embedded in the plastic about reading the service manual before messing with the throttle controls.

I'll fire it up and check with the trouble light to see if I can get a better guess of what the heck is making that noise. I don't hear very well, and I'm sure most folks would hear that noise outside of the car.

[Jeff_in_Atl]

easy way to check your alternator is going bad or not is simple. Start car, turn on all assessories, ie lights, fans, radio. Then unplug the negative terminal on the battery. If the alternator is good, then the car shouldn't die...if it does, then it's going bad.

Credit goes to Jeff95Z28

Very close. But I would crank the car without anything on then disconnect the battery. Then rev it to ~1500 RPMs. Then start turning on things. Turn on the A/C, slowly turn up the fan. Then the lights then high beams then rear defroster. If the engine starts missing or dies at any time during this the alternator or regulator is bad. It's a poor mans load test.

Thanks Chris

[TGregg]

From bad to worse

Thanks Jeff.

Well, I just went out to the garage and fired her up to use my trouble light to find out where that noise was coming from. She turned over, and that noise was louder than ever. The engine started to miss a few, then the noise stopped before I could get to the front of the car, then the engine died. I could see all the lights on in the dash, still had some power. This car has gone nowhere since that load test I did earlier, when the alternator clearly produced enough juice to idle the engine.

So I pulled the battery to recharge it, and it recharged in a minute, which usually means it was already nearly charged. It's only a 6 amp charger. I tried it on the 4 amp and 2 amp settings, both showed charged in just a little bit of time.

So I think the problem is my car is possessed by Cthulu, and I need a few priests to get her running right.

Seriously though, it can't be the alt, since the battery still had a charge, right? It's got to be either the wiring (and it can't be a short), or the PCM (or whatever it is) is getting senile. Either one sounds expensive and beyond my meager repair abilities. Any thoughts?

Also, is there anything special I should do before I restart? This car never stalled before today.

[Z Ya Later]

Hold on, you're saying that the alternator only has one wire on it and that's it? There should be another connector at the bottom that plugs into the voltage regulator. If this isn't plugged in, I would think it could cause a problem. Verify that the regulator is hooked up first.