Alternator not charging, what did I forget ?
 

Well the engine swap is done, car runs but now the alternator is not charging the battery

I checked the output of the alternator. Had nothing at the battery

Checked all the grounds, checked the charge back wire and connector on the alternator. All seemed to be secured

I did not have a good enough DVOM to check anything else but the voltage at the battery

First thought was maybe the alternator was damaged upon removal, stud for charge back wire spun. So I replaced the alternator and still isn't charging

What is it exactly that one wire does in the connector and should I have a certain voltage there ? or is it specifically for my gauge?

What could have happened ? what should I look for ?
Where exactly does that one wire go to so I can check to see if it is broken or shorted as well

Any suggestion or help is appreciated

Check if there's a blown fuse somewhere the same thing happened to me on my third gen it was a blown fuse

had no idea there was a fuse for the alternator. ....

I'll add that on my list

thanks

Your welcome man

Check and see if ur alternator is putting any juice out. Then trace it back to the battery. Dont think theres a fuse but i could be wrong

anything that runs electricity has a fuse on it, unless you want to melt stuff

The small wire goes to the pcm. Its usually referred to as the exciter wire online. The pcm controls charging output from the alternator. Alldata refers to a fusible link in the charge wire but I don't think there is one. There is no fuse in the circuit. If there is an issue with that small wire, the alternator won't charge. The large wire should have battery voltage constant and mid 13's to low 14's when charging. The alternator housing should show ground.

Thanks !

Is there a certain voltage that i should see from that signal wire. Like a 5v reference?

I'll check it all tonight

I think its supposed to be 5-8 volts but that's from googling around, no source worth noting.

alright.

I have a feeling its going to be that line. Probably open somewhere.

I'll ohm it out from the pcm to the alternator and check for a short.

thanks again

Yeah I think they have issues with it. Make sure the pin in the connector is ok as well. Your p/s pump isn't leaking, right? I believe its pin 15 on the pcm.

It was but i replaced both the pressure and return line

Yeah I get that here at BMW sometimes the pins will be pushed back into the connector and won't actually contact the pin on the component. But it did not look like it pushed back. I will triple check

But yes it was leaking. Already cleaned the harness with contact cleaner and used a little silicone around the weather packing to help it seal

IIRC, isn't the exciter wire activated by a signal from the cluster on the ls1 cars and not the pcm directly?

actually i dont know, nevermind me, ill keep thinking to myself lol

Ok, I just know its an issue with the pump leaking and killing the alternator. So the new one wasn't leaked on?

I think that is 98 only or 98-99.

No the new alternator was not leaked on. Vehicle has not left the lift since I first got this engine swap started

If everything is plugged in, chances of the new alt being DOA?

I could later on see what the exciter voltage is supoosed to be and let you know

Im gonna drop by the dealer and see if I can get a new pig tail.

I am curious what I should see there.

assuming the PCM controls the output it should be a range.

Or it could be PWM, but I don't remember off the top of my head.

Well after some checking of everything

what i found

-no power from the alternator at B+ on battery or at alternator
-ground from alternator to chassis is good
-ground from battery to chassis is good
-no voltage at excitor wire while vehicle was running
-pulled connector at pcm and connector at alternator found open circuit from pin#15 on red connector PCM to alternator pigtail
-made a jumper wire from pcm to alternator connector and alternator is now charging

New pig tail is already on order for tomorrow morning, going to create my own line with the new pig tail since i dont know where it is broken.

Appreciate all the help guys ! Hope to have it out and about soon

Good stuff. Maybe along the way it got pinched or snagged and separated within the insulation.

yeah I don't doubt it lol

Was this fixed?

yes. he did. he posted how he fixed it in his build thread.

sorry man. Yeah I found an open circuit on the exciter wire between the connector to the PCM pin #15 so I bought a new pig tail and connector from GM since the weather packing was screwed up and ran my own line from the alternator and spliced it into the pcm 6" away.

So far so good.

Ah glad to see you got it worked out. I just replaced my exciter wire connector too because it was screwed up even thought it was still working. I haven't checked in on your build thread for a while. Gotta check in to see how its doing.