87iroctheo

I was out in the iroc last night and slowly watched the voltmeter on my dash drop to the point that I was just about driving home by moonlight to get into the garage. Preswap the alternator charged great. I am wondering if it could be a poor ground causing the issue or if I missing something in the wiring? Any thoughts? My data log from the trip shows charge started the trip at 11.1 and coasted into garage at 9.1v (with nothing running but the motor...barely).

R13_Braz

If it started that low and ended even lower, then either the alternator is not working properly, or the PCM isn't sending a proper signal. More than likely, it's something with the alt itself.

87iroctheo

If I charge the battery up I get back to the 11v and can drive around for awhile again but it will eventually need recharging depending on how often I drive it. I know its possible but the alternator worked 100% before I pulled the motor. You got me curious about this communication thing, I wonder if someone could elaborate on this for me so,I could test my wiring.

Black18Ice

What year? The 98 needs a resistor in the exciter wire if you aren't using the fourth gen cluster.

R13_Braz

The chances of the PCM being the problem are very low, honestly. If you're draining the battery while driving, then the alt is not charging it. Take it off, find your nearest auto parts store that tests those things, and get it checked. Easiest first step.

Queball

if you got a volt meter...

car off your battery should read about 12 (if its dishing out lower then 12..replace battery.

turn car on, and slap the meter on the battery
your alternator should be dishing out around 13.5+ while running.
if its under 13...alt is bad...


a bad ground can cause some issues too, check ground on alt to battery n battery to chassis.

so recap..
check battery terminals for good connections
check grounds (ground strap, ground from battery to chassis, battery to engine block)
check positive ( make sure no corrosion is going on )
check alt wires, make sure there are no breaks in the wire(s)

check battery with meter for 12+ with car off
Check battery with meter for 13.5+ while car is running

if alt is throwing 13.5+ with car on, but battery isnt giving you a reading of 12 with car off
replace your battery.

you dont have a meter?
go to your part store.. they can test it without removing anything.

the dash gauge isnt accurate, per-say but .....yea...

87iroctheo

So I get 12.1v with car off and 11.9 with it on. I did not have a dedicated ground from alternator, just had motor ground in 2 locations. So I added a ground from the alternator casing to the battery (I was hopeful but it didn't change anything, but I think I will leave it regardless). The only other thing I can test here is the broken wires on the harness. Otherwise am alternator test would mean 3 mins of removal, 3 hours of driving to the city and me hoping the alternator doesn't test ok so that the trip is worthwhile. Looks like if the harness doesn't show anything I will just wait until we have a reason to go to the city.

87iroctheo

Its a 95 swap, and I am using my 87 stockcluster. My data log from scan9495 reads accurate I would think, so I mostly have been relying on that for measurement.

Queball

replace your Alt...the alt isnt charging the battery

the wires that connect to the alt make sure those look good.

other the that you should be seeing 13.5+ with car on..been there done that with my 92 RS..

*edit*..yea check what ya need in the harness..if nothing is wrong there....you should see a red wire
from Alt running to your Postive battery term (or maybe dist block)..check that too

87iroctheo

Well decided to take kids into city to watch street legal drags and figured I would detour and get alternator checked out. Of course it checked out fine. Back to the drawing board. I think I am going to really work on that ground and I will ohm out the harness and see that it intact. After that I am at a loss.

87iroctheo

Ok I've been learning about how all this works. Sounds like I need 12v+ at the harness during key on. I do not have that. Instead it seems my dash gauge wire is connected to the exciter wire (well it shows continuity with it anyways). I believe this is correct however I also believe their should be another wire somewhere on this same line that gives 12v+. Where should I be stealing that 12v from?

Queball

electrical sucks..i hate it myself..give me something mechanical to repair any day..lol

i would say back track to what you changed or might have missed.

heres some wiring diagrams
http://www.austinthirdgen.org/index.php?pid=19


if she was working b4 the swap, then something was over looked..from sounds of it..

87iroctheo

Ok, so no luck and frustration sets in as I have run out of ideas. It's pretty basic wiring from my understanding, maybe someone can correct me on this but here is what I figure...the alternator really has 2 wires going to it. 1 wire is a 12v cable from the battery positive. The other wire is the exciter wire from harness plug. Now, the lt1 harness c220 pin A wire (red) should connect up with my c100 bulkhead pin F8 (brown). This has been done but does not give me key on 12V at the exciter wire at the harness (so be it I can figure that one out later). So, I jumped power from a different circuit to the exciter wire so it has 12v+ at the key on position (run). I thought for sure this would do it, but no such luck, still same old 11.8v charge while running. Just a reminder my alternator had been tested and checked out "good". Also I added another ground strap from alternator bolt to body frame. Can anyone give any insight on what I am missing here?

87iroctheo

Well I have a conclusion so I figured I would update everyone so that the next guy doesn't fry a $200 alternator. Turns out the single wire lead to the alternator requires a resistor to trick the alternator I to thinking there is a warning light in the circuit which my stock 87 cluster does not have. I unfortunately tried to just give the single wire (exciter wire) 12v without the resistor in place and it effed up something inside and when I took back for testing the shop said it failed the light cicuit test, but out of 3 shops no one could tell me what that meant, except canadian tire where the kid told me it was an odd ball alternator and they didn't have the harness plug for it, I laughed that a chev 350 was odd ball, watching him trying to hook it up told me he wasn't the guy for job as is, turns out I was right....man I hate the peeps in the auto dept at can tire (usually). So I checked I to an alternator shop and they would charge $75/hr, plus I would have to get it to the city and pick it up, so I cut my losses and bought a rebuilt one for $170. Lesson learned, that's fine because I am so pumped that I got it working now (with a 470ohm x1 watt resistor inline) because if it didnt work and I fried another alternator I would be choked. So there you have it like Black18ice said in the beginning his 98'needed a resistor, well so does the lt1 in 95 (if your swapping into so etching without warning lights). Thanks for the help everyone...onwards to the fun stuff again....sub frame install.