truckguy

Tpi 5.7l 1990 firebird

truck died, got a jump, died again, got a jump, had alt tested, parts store rep said it wasn't charging.

Brought it to my house pulled the alt, brought it to autozone, had it bench tested and the batt charged , both were fine. Batt is new.

the question is still why did the first alt test show not charging?
I guessed it could be because the batt wasn't charged enough to power the alt but not sure, not experienced enough...



Anywyas what should I do now ? I want to rewire the alt to assure it is working fine. this motor was swapped into my truck which is a Chevy 75 , and wiring looks like crap.

henryd3

iTrader: (128)

Was the red wire from the battery solidly connected to the B+ terminal on the back of the alternator? It may connect from the starter, I forget, but needs a good connect on the alternator.
Did you first test it on the engine while running and it wasn't charging?

truckguy

Thanks for your response


There was a parasitic draw before any of this. I unplugged the circuit, replaced the battery, used a multi meter to test the voltage on the alt and the battery and they were both good. Then two to three months later this situation happened (drove it auto parts store died in parking lot) During the months in between ...I would make sure to take it out once to twice a week to charge the batt (this is my project truck not a daily). But when I finally took it out this last time it died.


So the red wire (the one that bolts on to the alt) goes to the fire wall, then I think there's another from the firewall to the batt. The terminal On the alt is some what wiggly but didn't seem to be an issue for the autozone guy I noticed it was wiggly when I was pulling off the plug (it was hard to do and required some force and I broke some of the plastic) I don't think this is an issue since it passed the test afterwards.

There's a ton of things that also go to the fire wall . Would it be smart to run it straight to the batt ? Or is it possible that some of the wires on the firewall need the alternators red wire ?


I don't care about ac or heater let me know if there's any more info you need, I need all the help I can get I'm working alone on this project.

henryd3

iTrader: (128)

Don't know what's going on with the wiring since it's in your truck, but unless the B+ terminal is connected to the battery it's not going to charge it. Does the wire show battery voltage when removed from the alternator?

bigal55

iTrader: (1)

Maybe this diagram will help. The Gen lamp must be good, it provides the excitation voltage to the alternator for it to start charging. It is not full battery voltage but around 4 or 5 volts (I believe). Without this initial excitation voltage, the alternator will not charge. Just something to check, key on engine off, check for voltage at the L(f) terminal. Another point, if the stud for the battery cable is loose, you could have a faulty regulator and if you have a parasitic current draw back into the alternator through the batt. terminal, you could have a bad diode trio (rectifier). Here's the diagram. HTH!

truckguy

not sure how to test this.. do I just set the multimeter to voltage and stick the positive to the red wire?

truckguy

UPDATE: did some voltage testing.

batt:12.6
fat red wire: 12.6
brown wire on the connector: 0
red wire on the connector: 12.6


after reading this thread , I decided to do some testing on the connectors ...and it seems like the brown wire is not working.

so happy that I have seemed to have found the issue. NOW how do I fix it?! lol

Tuned Performance

iTrader: (92)

The fan has a 20amp fuse, power goes to the fan relay (brown wire)
Then splices off and goes to the alternator.

bigal55

iTrader: (1)

If you look at the diagram I posted, you see the brown wire gets power through the Gen lamp from the ignition switch. As I stated above, is the Gen bulb good? With the key in the run position and the engine not running, you should see about 4 or 5 volts at the brown wire. Also, your GEN light should be "on". If you have 0 volts, the initial excitation to start the alternator charging is not there and the alternator will not produce any power. As shown in the diagram, the bulb (or the 10 ohm resistor for rally gauge package) drops the battery voltage to about 4 or 5 volts which energizes the field coil in the alternator. Once the alternator starts producing power, it becomes self exciting and no longer needs the 4 or 5 volt "initial excitation". You could get a 12 volt bulb and connect it from battery positive to the brown wire at the alternator while the engine is running. This should start the alternator charging. You need to check that brown wire and trace backwards toward the Gen light and then back to the ignition switch to see where you are losing the power. HTH!

Tuned Performance

iTrader: (92)

The brown wire is hot in run ign position

truckguy

Thanks, that's useful.

truckguy

Damn I thought I found the issue. I didn't understand what you meant the first post, now I get it. Correct me if I'm wrong this is my understanding...

-Brown wire is 0 when the car is off
-then with the key half way turned, the brown is 4-5v and gen lamp is on
If 0 voltage at key half way, then this will indicate an issue within the circuit (ignition switch wiring) then there's a problem.
-if all is good then 12vin the brown when engine is running

Without a gen lamp the brown won't be able to do 4-5 at half way
and if there is gen lamp and the voltage is 0 at half way then issue is within the ignition switch/brown wire circuit


Like i said the motor is in my 75 Chevy truck, so there might not even be the same stuff as a firebird, i.e. Gen lamp (swapped into by the previous owner, guy prob did kno what he was doing).....So I'll prob need to put a bulb in like you said, just not sure how...

None of the dash lights work, is that where he gen lamp is?
I tried googling it but cant find it, I'm not sure what it's suppose to look like, could you describe it ?

truckguy

UPDATE: alternator charging....?

installed the alternator and plugged the batt back in just to get some voltage numbers and some how...

12.4v engine is off
14.7v while engine is running ...so it was charging.
12.7 after engine is off.


while key was halfway
11.6 voltage in the brown wire pin ? (thought it was suppose to be 4-5 volts)??



!!VERY CONFUSED!! I didn't do anything to the wiring...
I will run it once a day for the next week to see if anything bad happens and keep testing it.

Tuned Performance

iTrader: (92)

I think if your using a idiot light and a 10 ohm resister you will drop maybe 3-4v.
Sounds like (brown wire) is wired to accessory 12v power.
With the vom inserted into the brown wire you might want to flex your harness to see if voltage drops or goes away. The splice may have a issue.
Looks like there are a few recommendations on resistance for a light. Painless says 5watt 82 ohm.

http://www.painlessperformance.com/Manuals/30705.pdf

bigal55

iTrader: (1)

OK, your truck came stock with a SI type alternator which is the diagram I posted above. The 90 Firebird came stock with a CS type alternator which is what Tuned Performance posted the diagram for. Either way, you need voltage at the brown wire going to the alternator. Being this is swap, we don't know exactly what was done as far as the wiring goes, truck dash with 90 TPI engine harness? From the diagrams provided, you should be able to figure the wiring, or at least what it should be. If you don't have voltage at the brown wire with the key on and engine off, you will have to trace back from the alternator along the circuit to find where the circuit fault is.
To answer your question about the Gen light, it is an indicator light in the dash. Usually to the left of the steering column and in the lower portion of the dash. This is old school before gauges became the norm in cars and trucks. As I stated above, I thought the voltage should be about 4 or 5 volts but wasn't sure. The voltage will be determined by the bulb's resistance and the field coil's resistance, but the level is really not important it's just that you need that voltage to excite the alternator to start the charging. Determine which setup you have and use the appropriate info given. Unfortunately, you will have to trace the wire back to see where it is getting its power from. Hopefully this isn't confusing you more and provides some help. GL!

truckguy

I will check for issues in the splice.

Okay wiring looks setup the way the diagram you have posted describes.
The wiring harnes should be for 1990 because it has connectors for and
ECU and plugs into an ECU. I do have a built in indicator bulb in the cab that could be the bulb.

I'm not completely lost, One last thing I'm confused about is why I need to find where the brown wire gets power from.

truckguy

okay 2days after I put the alternator in ... check it this morning (truck has been sitting for two days with the alt in) and it overcharged to about 16.6volts...

Im wondering if this makes sense because there is no gen lamp? why would auto zone say that the alt is good?

Tuned Performance

iTrader: (92)

I'm wondering if your battery has a bad cell or you have a parasitic draw.
The ecm draws 1/2 amp so it would take a week or more to cause a issue.

truckguy

the batt is about 4 months old.


bought the car,
bought the batt put it in,
parasitic draw killed it,
replaced it with warranty and also unplugged the circuit,
started the truck up every time till this "alt issue" (don't even know if its the alt anymore) ...
brought it to auto zone (4 days ago) they tested it it was fine.


its not draining the battery, it seems to be overcharging it now. I will see if the truck starts up, it should since theres about 12.5volts.

bigal55

iTrader: (1)

As described above, the brown wire is field excitation and needs ignition power to initially start the charge. If you are losing power at the brown wire, your alternator will not charge the battery. Depending on the setup, either the brown wire comes from the Gen lamp as would be normal for the 75 wiring or from the splice for the cooling fan relay as would be for the 90 wiring. If this wire is intermittent, you need to find out why. As for the battery over charge, that would be the internal voltage regulator. You said the Bat terminal on the alternator was loose in your previous post. I stated that that could be a problem with the regulator (or cause a problem with the regulator) and may be the cause of the over-charge. If you are using the CS type alternator (90 Firebird stock type), the S terminal doesn't need to be connected to any voltage source but it can be connected directly back to the Bat terminal on the alternator. The S terminal is a voltage sensing connection back to the regulator and tells the regulator the voltage level it needs to produce in order to maintain about 13.7 volts or so. Most swaps just connect the S terminal to the Bat terminal as this is simple and effective. The alternator then monitors the battery directly as the battery is connected directly to the Bat terminal. You can try making this connection but if the regulator is bad, I don't think it will help. FYI, if the S terminal is left un-connected, the regulator monitors the Bat terminal internally. Because this terminal is loose, the internal connection may be faulty and connecting the S terminal externally may help. GL! Keep us posted.

truckguy

thanks I really appreciate your feed back

yeah so I am really just going to disregard the auto parts store tests and also buy a new alt under warranty (I really don't know how old the alt is and it doesn't hurt to get a new one)

... and ill test the new one to see what it does. if there ends up being no problem ...well at least I know how the wiring is setup.

thanks again.

Tuned Performance

iTrader: (92)

Like bigal55 said sounds like the regulator is bad in the alternator.
Not sure how much a new alternator is but the si and this can are easy to rebuild.

truckguy

I need this question answered.
my question is ...
"is 'over charging' that happens ONLY when the engine is NOT running a sign of a faulty voltage regulator?"
this is the exact case I am having right now..

I just need to be clear of that before I buy a new alternator. I am confused a little as I assume the voltage regulator's job is to regulate the voltage WHILE the engine is charging (which is when the engine is running)
...and since I'm getting 14.6 volts when the engine is running id say its doing its job, no?

Tuned Performance

iTrader: (92)

I don't see how the battery voltage can increase without being charged, alternator or with a battery charger.

truckguy

I will wait an hour or two with everything plugged in and see what the voltage goes to ...but theres no doubt I'm definitely seeing an increase in voltage.

possibly will bring it to a mechanic as well..
also considering getting a new engine more appropriate for the truck and just doing a fresh new wiring setup.



update: just found a blown fuse for the accessories circuit. going to replace and see if that has anything to do with it.

truckguy

UPDATE:

finally found the source!

last I posted the alt had fixed it self and everything was operating fine
(consistent ~12v when off and ~14.5v when on) and I had found a blown fuse (lol that I think I blew in the process of finding the alt issue)

luckily I did blow an ACC fuse and luckily I saw it. It lead me to believe that the theres an issue in the circuit.

So I put the fuse back in, bought a cassette tape from the store, and ...
- tested the batt with the music on engine off nothing
- headed to the gas station tested the batt with the engine running and music on and ..12v at the batt!
- unplugged the fuse while engine was running (so I didn't die on the road) and instant 14v
charged, filled up went home.


plan is to live without music will I get the truck painted... then eventually swap for a carbed engine instead of the this TPI in my 75 chevy step side, not sure why the previous owner even went through the trouble of putting this motor in in the first place lol.