Ammeter gone crazy

[msbaugh]

My ammeter has started oscillating back and forth like crazy. Only at idle, once I rev it up and get the alternator spinning it steads out at charging. This all happened convienently after I put my new ecu (rev n nator) on. It put so much timing in that I had to put my chrome box back on. Now my gauge is going crazy I'm thinking its my regulator or my alternator

[Katfish]

Similar thing happen to me when I changed voltage regulators.
The bolts had vibrated loose, check your grounding.

I added a strap and it fixed my jumpy gauge.

[MEK-Dangerfield]

This wouldn't have anything to do with your new ECU.

The VR would be my first suspect.

[dodj]

I would go over all the connections. Bulkhead, valve cover etc.. I agree with MEK, it has nothing to do with your ECU. But charge/discharge has A LOT to do with clean connections.

[msbaugh]

Ok could the mounting bolts of the ecu cause this? Does the bolt ground the ecu or something? Maybe it came loose.  It only started doing this after my swap. I was stranded on the road but luckily had tools to put my old chrome box back on. Then I was able to start it back up. How could my VR all of a sudden go bad from the swap?

Weird thing... When I first put the rev-n-nator on I checked and set initial timing at 12 btdc, the car kept dying until I was eventually stranded. I swapped back to my chrome on the side of the road and checked initial timing and it was then at 22 btdc!! What the heck? I think it maybe wasn't grounded good enough, part of my firewall is fiberglass I need to check that

[BS CUDA]

Ok could the mounting bolts of the ecu cause this? Does the bolt ground the ecu or something? Maybe it came loose.  It only started doing this after my swap. I was stranded on the road but luckily had tools to put my old chrome box back on. Then I was able to start it back up. How could my VR all of a sudden go bad from the swap?

Weird thing... When I first put the rev-n-nator on I checked and set initial timing at 12 btdc, the car kept dying until I was eventually stranded. I swapped back to my chrome on the side of the road and checked initial timing and it was then at 22 btdc!! What the heck? I think it maybe wasn't grounded good enough, part of my firewall is fiberglass I need to check that

 I have had new VR's last only a day - I keep one in the glove box. The best luck I have had is with the cheap $8 ones - The $30 Chrysler ones can stay on their shelf 

[msbaugh]

So I put a new electronic voltage regulator on.  It ran great for a little bit, then the charging system started going crazy!!! The ammeter was bouncing all the way from discharge back to charge... it even cut off on me while I was driving on the highway. I sure pissed the guy off behind me... IS THIS MY ALTERNATOR?? I don't undersand!! I was able to get it back going and get home but the ammeter is still bouncing around everywhere

[brads70]

I think it maybe wasn't grounded good enough, part of my firewall is fiberglass I need to check that

Why is part of your firewal fiberglass? Does the VR bolt to metal?
 (grounded on bare metal?)

[msbaugh]

Yeah my initial thought was because of the fiberglass I wasn't getting a good ground. 3/4 of my firewall is fiberglass it's some wierd drag racing cut out someone did in the late 80s. There's still metal left though and the regulator and ecu box both  have good ground. The voltage from + battery to voltmeter ground is fluctuating like crazy.

[dodj]

The voltage from + battery to voltmeter ground is fluctuating like crazy.

Run a test ground from battery -ve to the VR case. See if you get a constant voltage.

[mopar jack]

If your amp gauge is cycling very fast from charge to discharge you could have a bad diode in the alternator. That would cause the charging circuit to put out A-C voltage instead of D-C and that can cause problems with your ECU. Put a volt meter on the output of the alternator and check for AC voltage.

[msbaugh]

If your amp gauge is cycling very fast from charge to discharge you could have a bad diode in the alternator. That would cause the charging circuit to put out A-C voltage instead of D-C and that can cause problems with your ECU. Put a volt meter on the output of the alternator and check for AC voltage.

I feel like that's the only thing it could be! I'm going to check that out

[msbaugh]

So I keep updating this because I haven't had time to solve this issue.  I pulled the alternator, here's a picture.  Its a square back, one wire style alternator from a 70 and later vehicle... Its got the battery connection and the two FLD connections... also some doohicky on the back of it as you can see, maybe y'all can tell me what this is? Is it some sort of external diode? What does it do? I have an external voltage regulator on the firewall so this can't be a VR right because I wouldn't have two. 

Ive been tracing my issues and I went to autozone to get the alt. tested. It came out saying it was bad, but I'm not so sure.. the guy had no idea what the F he was doing.  Also I have no clue what the output rating is I never tried measuring it. Now that the current is fluctuating so much how do I figure out which one it is? It's a tough stuff alternator, I need to figure out what is causing this I want to drive my car before I move offshore for work

[msbaugh]

Turns out that little doohicky is a universal voltage regulator... So I have two voltage regulators on my car, one on the alternator and one on the firewall.... 
I got the alternator to spin on a pros machine who does nothing but starters and alternators and generators and he said everything tested out perfectly fine.... WHAT THE FFFFFFFFFFFF

[msbaugh]

Well I ended up taking a full day to re-wire the whole engine bay. I got a new VR and wired it up on the firewall following some wiring schematics I came across online.  I wired it up and ditched the old VR and re-soldered a ton of new wire replacing some very crappy crimps and splices.  The wire from the alternator + was only a 10 gauge wire taking all of that current. (I measured was around 60+ amps from the alternator). Once I got the wrap all off it I found that it was burnt up in places and for some reason had way too many butt connectors, fixed that real quick.  I then disconnected the ammeter and put a temporary voltmeter in parallel with that wire.  No more fluctuations and it is running good!!! I have no idea what was causing that in the first place but I assume it was the VR