I posted this on LT1 nation on facebook. I am almost at the point where I am going to just throw money at it and buy a bunch of new parts which my gut tells me is a waste.

I've searched the net and have not found anyone have this problem.

My alternator died. Car runs fine with the dead alternator on and running off battery. Idle is fine, all checks out fine and can drive down (not far as on battery only) the road and back.

I buy a new high output alternator and put it on. The car will barley idle, runs super rough, will not respond to throttle inputs. It seems to be loading up on fuel as the IAC maxes out. Volts jump a bit.
I borrow a known to be good alternator from my buddies 97 bird and runs the same shitty way.
I'm getting 11.5V key on engine off at the exciter wire and the connector. I've beefed up both pos. and neg. cables to the battery and even used jumper cables to test. Checked grounds or bad wires to starter. All seems good but it's not. The battery seems fresh and is always on the battery tender and has full charge.

Anyone out there sees this before or have any ideas??
Thanks

 

What voltage reading are you getting off the alternator wire when the car is running?

 

TTS has it jumping from 12.9 to 14.1 with it mostly in the 13.3 to 13.6 range.

Are you talking the positive red cable or the exciter wire?

 

Cable that connects to the battery. If those are the readings on the new alternator it is bad. It should be holding a very steady voltage of around 14.3 to 14.5 IIRC. Voltage should not be jumping at all. What brand is this new alternator and where'd you buy it?

 

erratic and low voltage like this will make a computer car run like ***

 

It is a Mr. Alternator (South Carolina) 200 amp that a few guys here have used without any issues.

I would agree with you (and would drop the bucks to get another alternator if it solved the problem) but I had this new 200amp one test at an alternator rebuild shop and it came back OK AND I took the stock alternator off my buddies 97 bird that he drives with no problems and tried it on my car. Even my buddies stocker ran like crap in the exact same way when I tried it out. He then put his alternator back on his car...no problems. So I could buy another then possibly have 2 new alternators. I would like to try this 200amper on my buddies car but I don't think he wants the bad mojo on his car.

Looking at logs.. fuel, MAP and IAC (maxed) are all way higher when comparing bad vs good alternator...just trying to idle. I do have an ignition box, LJ-Acceleronics injector box and dual fuel pumps but it all ran great for years. The car was running at around 13V before the alternator crapped out. I do know it was the voltage regulator that let go.

The new one also came with a smaller pulley and had to get a shorter belt...man I'm grasping at straws now. lol

 

If the voltage is fluctuating on the charge side to the battery as you say then it is not good.

 

If I remember correctly you've been fighting this for a while?

I don't know what a LJ-Acceleronics injector box is,(impedance converter?) but injector timing changes with voltage in the PCM. A tune done with a weak alternator could be a cause.

I would pull the ignition box out of the equation, check PCM grounds.

I have seen aftermarket HID kits cause similar issues, though only when on.

 

Yeah, I worked on the car all last summer hoping to drive it in Oct. only to have this pop up which I though a new alternator would be the easy fix.

I did try to change the tune a little last fall in the injector offset tables. That didn't help. Next would be to trick the PCM by raising the injector constant but I'm not a fan of tricking the computer but I will to see if something will work.

I am think there is two ways of looking at this:
1- It is a simple charging problem. It must be alternator, cables, ground, battery, exciter wire or fuse problem. I've looked over all these but will look at the battery and cables again today and bypass the ignition box.
2- The car is adding a bunch of fuel not allowing the RPMs to get high enough for the alternator to do its job. It struggles for 500rpm and likes 850rpm. Yes the higher voltage will make make pumps, impedance box, tune add fuel.

My buddy said it runs so nice on battery alone that I should fill up the trunk with batteries and have a hybrid.

 

For those keeping score:
-After 6 hours of not charging the battery is 12.79V and is 13.1 fully charged.
-Bypassing the ignition box didn't help or change anything.
-SS RRR: Measuring at the battery terminal while the car is running, the volts were jumping mid 13s to low 14s and so was the exciter wire but not sure it they were in tandem. Something I thought odd.
-I put in fresh plugs in a week ago. After 3 minutes of garbage run time the plugs are black and sooty. The ones I pulled were dark black. You can smell the gas in the engine bay as it runs.
-Checked for continuity on every ground I could find.

Next up is to jack up the injector constant in the tune and see what happens. I'm not confident on this.

One thing I am looking into is the big *** silver fuse for "Batt" in the door panel. I didn't check any of the silver fuses. I pulled the Batt fuse and you can't tell if it is dead like a plastic fuse. I have never monkeyed with these fuses in the past. The dash still lit up with the fuse pulled.

 

The silver "fuses" are circuit breakers.

 

How do I know if it is bad?

 

You can check for continuity with an ohm meter across the terminals. It should measure less than 1 ohm but that is only checking that it is not currently open. It is possible to ohm good and not be able to carry a load.

"The big *** silver fuse in the door panel" I am assuming you are looking in the fuse panel on the drivers end of the dash? The typical circuit breakers in that panel are for power windows and I think power seats.

 

Couple other thoughts; If you can run your injector box from a separate 12 volt source not connected to the cars electrical system.

Monitor fuel pressure with the alternator connected/disconnected, should not be more than a pound or so difference.

Edit:
Also found this vid, may give some insight.

 

There are 3. Batt(ery), PCM Ign(ition), and acc(essory). The one I pulled is 30 amp 12 volt.

 

What all has been done to the car(any and all mods)?

Have you checked the fuel pressure when the idling issues are occurring?

If the engine is having trouble running(ie, the engine speed is all over the place), then I would expect the voltage to move around some if the engine is almost dying.

Strange that is okay on just the battery. Makes me think that some component is having trouble when the alternator bumps the voltage for charging. If so, trying to isolate it will be the trick. Depending on what went bad with the other alternator, sometimes it can take other components out with it.

 

Kevin had a good suggestion in your last thread. Is the alternator painted in any way that could cause ground issues? Any signs of bad wiring(green or rusted terminals)?

 

In my 1997 Camaro the fuse chart list two breaker locations #12-30A breaker for Defog/Seats and #15-30A breaker for Power Windows.

The area labeled Batt and Accy are not fuse locations but up-fitter taps, a single blade intended for easy access of power depending on Ignition switch position. There is one more labeled Ign.

PCM Ign, position #13 is listed as a 10A fuse not a breaker. Its possible something is going on there.

Fuse chart: http://i19.photobucket.com/albums/b1...pse76f118e.jpg

Not sure what year your ride is, it may be a different lay out.

 

A very differnet average voltage than what the tune was set to will mess with your injector constants, so that will def not play well with things.

As someone pointed out, make sure have a solid grounding path for alternator case. I used an empty bolt thread on the case to run a 1/0 to chassis ground.

 

Supercharged 355. It is a early 2000's build. Lonnie's dual fuel system, Acceleronics Versafueler (impedance converter before big injectors became available), ignition box.....

Engine speed is not all over. It just struggles to stay alive. It will not even respond to throttle inputs at all. Runs awesome on battery.