Replaced Alt and Battery, now what???

[itzstreetlethal]

I'm getting a little annoyed. The once solid LT1 is starting to worry me and has left me on the side of the road TWICE recently. It's got an electrical "anomoly" and is only running on battery.
Long story short, I noticed driving one night that the idle started to get rough and the car was losing power (literally), the headlights were dimming and I barely made it home. So next day I swap in a fresh battery and things seem better, but not for long. Stumble and studder are back and I pull in to the local car parts place where they troubleshoot the problem and sell me a new Alternator. I swap that in and again all seems, till I shut the car off back at the auto parts place to return my core. The car won't start and I'm starting to get a little pissed. Spent about $180 on the new battery and alternator and I'm wondering what else in the system could be the culprit. Ign module? Got a bad Alternator fresh out of the box? I'm afraid to drive it because I don't want the car to die again on the side of the road (was a good two mile walk in 95 degree heat, home to get ANOTHER battery) and I don't want to damage the fuel pump, ECU, ing module, etc running on low voltage. I did fully charge the battery before running around with the new Alternator and after a brief ride, I disconnected the battery to test it. The car shut down immediately, like I turned off the key. Any ideas? Areas to test or try? Thanks.

[shbox]

You mention nothing about voltage. What is the voltage reading engine off and engine on (on gauge and with a meter at the battery)?

[Blubird]

its not really a good idea to do the "old skool" tricks of testing things these days.there must be something draining the power somewhere.

[itzstreetlethal]

I'll have to check voltage but it's a VERY simple setup. The car was gutted and runs a simple "painless" type harness. The stock gauges are not installed, no interior lights, no radio, fans are manual, no a/c, etc. I did a racetronix fuel pump upgrade with harness but that all looked fine when I swapped in the new alternator. Car is parked (stranded?) at work but I'll do a double check on wiring and see if I can get my meter on it to check voltage at the battery. I do know the cranking amps were low before I bought the new battery, around 325amps but I slow charged it (till green light) and still had the car die a day later after running on nothing but battery. Bought, charged and installed the new battery and that's when I did the "old skool" test. Just refresh my memory, my old LT1 showed like 12.7-13.1 on the scanmaster for battery voltage. Should I look for closer to 14 volts (on the VOM) if all is well? Thanks again.

[itzstreetlethal]

And just so there's no confusion, the fuel pumps' been fine since I installed it months ago. Have many 100's of miles since that was installed. I know it's voltage related because when it first started this problem, I had the headlights on. When I was troubleshooting, the car would "wake right the fxxx up" when I'd shut the headlights off (conserving juice for the ecu, fuel pump and ign). :hmm:

[Blubird]

Well from what I heard the computer reads the stock gauges for a power source so it tells the alternator how much to charge.

[shbox]

Well from what I heard the computer reads the stock gauges for a power source so it tells the alternator how much to charge.

Not exactly. The computer does not interface with the alternator. itzstreetlethal, do you have an exciter wire run to the alternator? The small, wire normally goes to the gauge cluster on a stock car. The alternator will not put out any voltage without it. If you don't have one, run a +12v wire with a 470 ohm resistor inline (must have the resistor).

[itzstreetlethal]

Hmmm, this could be a good starting point. It's a 1993 ECU (speed density) and harness. I did recently unplug the instrument cluster because the tach (and e-brake for some reason) wire was cut by the previous owner to run a monster (ricer) tach. I'm in the process of installing some of the interior and unplugged the cluster to fix the wiring and reattach the OE tach signal before the dash goes in. I'll have to plug it back in this afternoon and see if this clears things up. Thanks!

[itzstreetlethal]

Rob, let me check one of my favorite f-body resource sites and see if I can find this "exciter" wire. I do have the standard OE type wiring (plus fuel pump harness) to the alternator but will confirm the exciter runs to the instrument cluster! Thanks for the advice and direction to start troubleshooting.

[shbox]

Rob, let me check one of my favorite f-body resource sites and see if I can find this \"exciter\" wire. I do have the standard OE type wiring (plus fuel pump harness) to the alternator but will confirm the exciter runs to the instrument cluster! Thanks for the advice and direction to start troubleshooting.


http://shbox.com/ci/ci417.jpg

[itzstreetlethal]

THANKS! I think I also found it on one of your .pdf schematics as well.

http://shbox.com/1/starter_charging_93.jpg (red wire from the generator but I'm a pictures guy, THANKS ROB!)

Love your site by the way. Been a huge help to many with a passion for LT-1's and tons of useful information for others as well.

SO if I'm understanding this correctly, without the "exciter" wire running from the alt to the instrument cluster, the alternator will not charge properly?

[shbox]

THANKS! I think I also found it on one of your .pdf schematics as well.

http://shbox.com/1/starter_charging_93.jpg (red wire from the generator but I'm a pictures guy, THANKS ROB!)

Love your site by the way. Been a huge help to many with a passion for LT-1's and tons of useful information for others as well.

SO if I'm understanding this correctly, without the \"exciter\" wire running from the alt to the instrument cluster, the alternator will not charge properly?

That's right. The alternator will not "turn on" and output any voltage without it.