Looking for some help on my FD, I’ve got some issue with the electrical system.

When driving the system functions fine but then after a while I start to get a slow voltage drop until the car doesn’t have enough voltage to stay alive. Today it died in my driveway started below where it should be at 10v and then slowly dropped all the way down to below 6v where it died. The battery when it died has 12v so right where it should be. It’s on a trickle charger now but once it’s full I’m going to start it and pull voltage readings off the alternator. Hoping for any ideas on what this could be.


I’ve already replaced the alternator with a brand new one a few months ago and now the symptoms are back so it’s unlikely to be a bad alternator and I’ve also replaced my negative and positive battery leads

 

Twice this year my voltage was dropping like that. Both times it was fixed by cleaning the corrosion off the connector to the alternator.

I don't know why suddenly the corrosion was building up there, whereas I had no issue like that over 50,000 km of driving prior to this year.

 

What did you use to clean it? Just electrical contact cleaner?

 

Fine grit sandpaper.

 

I had this same problem a few years ago; turned out to be corrosion on the heavy power conductor, at the crimp on the ecu connector pin. I forget the pin #, but it was close to one of the ends. There was visible copper sulfate on the wire at the crimp and it was severely corroded. It appeared as though a chemical had leached out of the wire and caused the problem.

I cleaned it up, fixed the connection and was good to go.

 

a lead acid battery reading 12 volts is actually at 40-50% charge, lithium and AGM even less. was it 12.6? or 12.0? tenths of a volt are important when talking about batteries.

if you're reading voltage dropping, it's obvious your charging system isn't keeping up.

if you're reading over 13.2 volts engine running at the battery but still only getting less than 12 inside the car, then i would consider checking your fuse block battery connections.

you need to start checking voltages at various places. at the alternator, at the battery posts, at the battery terminals(not at the posts) and then at the fuse block in your engine bay.

 

I think it was around 11.8 on a lead acid battery. I cleaned the terminals and the car is displaying proper voltage after I trickle charged it for a while. I’ll keep monitoring it but voltage for the car is reading around 12 right now (don’t remember the exact value as I write this)

 

Loose fan belt?

 

sounds like your alternator is dying to me, losing it's output when it gets hot. or not putting out anything at all.

 

I don’t think it’s a loose fan belt. The tensioner makes it pretty easy to ensure it’s taught. I’ll double check it regardless

 

it’s the 3rd alternator since 4th of July, the one the car came with had a bad bearing, the replacement had issues within a month (could be the same issue I’m currently having) and I’m now onto my third. I think it’s unlikely I’ve got two bad alternators in a row from rock auto, I think I need to do some multimeter probing on the engine harness to see if I’ve got too much resistance or remove it to inspect the whole run for corrosion

 

Rats don't seem to particularlly like chewing FD starter harnesses, unlike my Hondas. But you might still check for that.

 

yeah I think I found the issue, I think the wire was failing and then it finally gave up yesterday or this morning because the car just wouldn’t start. I’m going to repair it but I’ve ordered a used engine harness I can clean up and install to replace this one

 

Post harness repair I get 13.8 v immediately on start. So yeah harness issue. Thanks for all the help!