BadVRod

Having a few gremlins and need some advice.

I have swapped a 96 LT1/4l60e into a 79 Firebird. The car is running but I'm having a voltage issue. If I charge the battery overnight, I can crank the car in the morning and the voltmeter reads 13+, but as the car idles, the voltage gradually drops. If I drive the car, the voltage drops much quicker. I'm thinking it's a bad alternator, but it's a new reman and I had it tested and it tested good. But if the alternator is on the car with it running, the output from the alt is only .45 volts without the battery wire. Also had the battery and ignition module tested. They tested good as well.

The last time I drove it, the voltage was around 10 when I got on the road and the car wouldn't shift. The gauges started to dance and I made it back to the shop and turned it off. After that it wouldn't start. I even re-charged the battery and it wouldn't start. No fire. Then after a couple of hours, I tried to start it, and it started right up.

Could the no-start and no-shift conditions be a symptom of a bad alternator or battery?

kaganader

iTrader: (11)

My old car had a similar situation like this and it turned out to be a bad battery. I put in a new one and all these symptons you described dissapeared.

shbox

Sounds like the alternator is not working. Is the exciter wire hooked up (little wire on the alt)? It won't charge without it. It needs switched +12v with a 470 ohm resistor inline.

BadVRod

That's the only wire I havent tested. Will do this morning. I assume if the wire is getting 12v, then the alternator is to blame.

BadVRod

Ok, I got 12.3 volts switched power to the exciter wire. Guess I'll take this alt to another parts house and have it tested.

BadVRod

Took the thing to Advance Auto, failed three times in a row. Took it back to OReilly's to swap it out, they tested it three times and it passed, but they said they would exchange it. None in stock, so I wait. I'm just gonna order an AC delco...

shbox

Got the resistor in there, too? Won't work without it (or built-in resistance from the gauge cluster).

BadVRod

I had the engine harness modified to accommodate the swap, so I am unsure about the resistor. How do I test for it? And if none is present, how do I add one?

The gauges are aftermarket and for voltage I just tapped the original voltmeter plug for the signal.

Again forgive my ignorance, I'm cutting my teeth on this thing and just want to get it right. I'm stumped as to why the alternator tests good one place and bad at another. One thing though, when I first got the engine running, it seemed the alternator was working since the voltage on the meter would increase as RPMs increased. It no longer does that. I paid attention at the time because it was the first time the gauges and engine operated together.

jaycenk

iTrader: (1)

test both ends with a multimeter set to ohms NO POWER on the line. then if it is there the M/M should read it as 470 or 47 or .470 just make sure you have it det to the right setting and it will read 470. If there is nothing there see if you can get a 470 ohm resistor and if not make one with other resistors. tieing them end to end increases and wrapping both ends side by side decreases.

shbox

If it is going to the original volt meter in the stock cluster, then it has the resistance built in and you should be ok. As soon as you start the engine, you should see the voltage increase showing that the alternator is working. If the alt tests good at one place and not another, I would suspect it is something one of them is doing wrong or their test equipment is faulty.

jaycenk

iTrader: (1)

I had that problem this morning. I bought a reman alt and had them test it first before I bought it and what they do is get the correct plug (for the exciter) and hook everything up and then apply load. This will not work because of what SHBOX is saying. The guy at the parts store said hum it's not working and I said you did not energize the igniton circuit (Exciter). as soon as he did that, the voltage shot up to 14.5 so make sure they tested it right. By the way this thread help me out this morning because I would have never had known that before I read it last night. Thanks SHBOX!!! Again!!! lol

BadVRod

Ok, new alternator installed...had it tested and it tested good. Brand new battery - Optima. Starts every time now, only still not charging. Must be the resistor. A guy at the parts house agreed...said he used to do EFI swaps into Jeeps and they had the same issues.

So...I've been trying to find the "other end" of the exciter wire. Can't find it on schematic. Want to test the resistance so I can either eliminate it or fix it. Any ideas on where it is? Does it go to the PCM? Sorry to keep being a pest, I'm just persistent when it comes to these kinds of things...

BadVRod

I've read up on this and now I have an understanding of the situation. From what I understand, the car the engine came out (96 Z28) of apparently had an idiot light for the charging system. This idiot light provided the necessary resistance for the exciter wire. My car, however, does not have an idiot light wired in. Now I need to test the exciter wire for resistance to verify this and add a resistor if necessary.

For testing the wire, as jaycenk mentioned, I would test both ends of the wire for the resistance, but I don't know where the other end goes. And there I am.

shbox

I have no clue on the wiring of a 79 'bird. But you said you put 12v on the exciter wire. Wherever you connected that up, just add 470 ohms of resistance inline.

BadVRod

Thanks Rob...I think you actually answered my question in another post. I've been searching and reading about this all night. When I tested the exciter wire, KOEO, I did indeed have 12.3v, however I was ignorant to the resistance issue. You've enlightened me.

All I should need to do is check ohms between the exciter and the battery + to see if I'm getting the resistance or not, then add resistor if need be. So I'll check that in the morning and see what comes up. I REALLY hope that's the issue. Seems like an easy fix.

Thanks to everyone for your help thus far and your patience. I'm not electrically inclined, but I'm trying to get better.

BadVRod

Got the charging problem figured out. Ran a hot with a resistor to the alternator in place of the exciter wire, got full charge on the battery ,showed charging on the gauge. Problem solved.

Now I am back to the no-start situation. Drove the car to get the operating temp up, brought it back to the shop, turned it off, tried to restart, wouldn't start. Cranks over, just won't kick-off. Scratching my head again...any ideas?