**UPDATED on Sunday, May 3rd, 2009**- see more info below in my last posted reply....**

This is my first post on here in a long time...!

I've got kind of an odd problem that I'm not sure how to resolve. I think it's related to the alternator, and how it's excited, but I'm not sure of some specs when I measure...

If the car is 100% fully and completely charged (12 to 12.4v), it will start OK. If it's just a little down (11.5 to 12v), the started kicks like you would expect it to if a battery was low, but it kicks HARD like it's being stopped by something. If the battery gets a little lower, it won't even click the starter. The volt gage & lights don't even really vary. Now, when this happed a couple of years ago, a mechanic friend jumped 12v from the ignition circuit (ignition, not constant) to the single wire going into the alternator, and it would start perfect, even when voltage was a little low. However, it seemed like this caused the battery to drain pretty quickly. If I remove the jumper and measure voltage to that wire when the car is running, it measure less than the battery voltage itself. I know this is pin 15 on the red connector of the PCM- does this lead intentionally put out less voltage than whatever the nominal battery voltage is? Also, the voltage does not go up at all when the car is running, So something is either wrong with the exiter circuit, or with the alternator itself.

I know it could also be a bad alternator or regulator, but it's pretty new, and it's had this probelm from the start. I'm a little concerned that it might be a PCM issue; could the mechanic have damaged the pin 15 circuit by backfeeding it with 12v direct??

I'm at a loss; I don't what else to look for. I tried to search for info about this problem, and couldn't find any descriptions that matched my symptoms.

Thanks in advance for any help! I typed up a brief histroy below of what I've been working on.

Sincerely,
Jeff Breeze

I have a '96 Buick Roadmaster that I've swapped a '99 WS6 LS1 driveline in to. This has not been an easy swap, thats for sure! But, for the most part, I've gotten most things working. I started this over two years ago, but shut it down about a year and a half ago because we had a baby & house renovation. Now I'm really trying to get it running again, as this is my daily driver.

 

The more I think about this, the more I suspect the alternator is bad. Does anyone know or have the spec of what the Pin 15 on the Red ECM connector should read (voltage) when the car is running at idle? I would assume it to be a percentage below what the battery reads, so as the voltage on the charge side drops, (say to 12 volts), the lead would fall to something like 10 volts, thereby kicking on the alternator charge field, and raising the charge side voltage back to ~13.5, and consequently raising the trigger lead to 12v, effectively shutting down the charge field until the voltage drops again...?

Thoughts? I guess I could go ahead and buy an alternator, and go from there... I could always return it.

Thanks,
Jeff Breeze

 

http://www.youtube.com/watch?v=Q3vCW8AdqMU

OK- so now I'm getting a bit desperate. I have a new alternator, new battery, and all cables have been loosened and re-seated. I'm at a total loss. I went ahead and shot a video of what was happening and uploaded it to youtube. I had my wife try to start the car. The voltage doesn't appear to vary much at all, so I'm not at all sure what the issue is. As soon as I put my charger on 200a boost charge, the car will start.

HELP!!! ANY help would be greatly appreciated!!!

Sincerely,
Jeff B

 

this sound like a starter problem not an alternator. When the solenoids go bad on the starters they tend to click. Ohhh please dont bang the starter with the hammer that would damage the starter.

 

So maybe that little extra bit of voltage gets the solenoid going? This may be a stupid question, but I'm kind of old school on stuff like starters; I'm not even sure I've ever replaced a starter on any of my newer cars (I've rebuilt several old small block chevys). Are the solenoids a separately replaceable item, or do you just swap the whole starter assembly?
Thanks!!!

 

You should be able to get just the solenoid but if it was me i would just go ahead and get the whole starter.

 

Sounds like a bad connection somewhere... if you've checked all your ground and pwr connections than maybe try what Chico suggested!

 

But its so fun lol....

 

FINALLY- a resolution...

I found a very unexpected culprit for my starting problem. First of all, in answer to my question about the lead to the alternator, a LS1 PCM sends a reduced voltage signal to the "L" terminal on the alternator. This was wired correct until the bozo mechanic added the 12v accessory tap. I have removed that. Alternator is now correct. As far as the starting issue, I found out I had a bad VATS relay. The VATS system was allowing the ground to pass to the relay on crank (as my factory key is correct), but the relay contact must have been arc'ed over time, which is why at 12 volts, it would stutter, but at 15 volts, it would crank. I wired in a new relay, and just grounded the coil wire on the relay rather than let the VATS do it, and WHAM- starts perfect every time. Too bad I replaced the starter before figuring this one out!!!!

Thanks to all who read!!