I think the first time I posted this it was too long, so I'll be brief. My alternator won't charge my battery. Replacing both the alternator and the battery did nothing. Voltage on alternator reads the same as the battery, 12V. Same if car is on or off. Problem goes away then comes back after a couple days.

EDIT: apparently this intermittent problem still hasn't gone away this time, making it easier to diagnose. I found the cause of the problem to be a 2.5 ohm (5 amp) short. So I'm going to go to town with my voltmeter. Any tips would be appreciated. Car still ran great, btw, as long as the battery lasted.

 

Probably a re-man alternator?

I'd question the voltage regulator's shape if its like many AZ/NAPA cheap-o re-man's I've seen.

 

isolated cause to the 60A BTN fuse. So I started pulling the smaller fuses and found the cause to be the 7.5A "ROOM" fuse. What the heck is that? I also noticed tht the ohm meter reading keeps changing. It's at 15 ohms now. EDIT: now 30 ohms. Weird. Maybe the problem is starting to "go away" again. Car is cold: has been sitting all night and the ohm reading just changed now as I was fiddling with stuff by the battery.

Oh well, my fault for not checking for shorts. And I even blamed the Haynes manual when that was the one thing in the Haynes manual I had to skip b/c I had no test light. Should have just used my ohm meter in the first place.

After my battery recharges I'm going to pull that fuse and see what doesn't work.

 

okay, I found this:
So I'm going to pull the fuse and go without my clock and dome lights for a while. Anyone know which one might be causing the short and how to fix?

And for those searching... always disconnect your battery and measure the resistance to check for a short before replacing/blaming your alternator and/or battery.

 

Pull the small plug off the alternator. Put a meter on the BLACK/WHITE wire with the key to ON. You should have 12vdc. Yes or No?

With the small two socket connector CONNECTED to the alternator, backprobe the WHITE/BLACK wire and turn the key ON. You should have 1-3 vdc. Do you?

Pay close attention to whether your on the black/white or the white/black when doing the above. Don't mix 'em up when checking.

Also, when the key is to ON and the small plug on the alternator is connected, do the idiot lights come on the dash? All of them? Should.

There is a free, online download of the FSM available. Download the ENGINE ELECTRICAL section. If I were you I'd look at the section called ALTERNATOR

The 15amp ENGINE fuse powers the black/white wire on the small alt plug.
The white/black wire goes to the CPU and supplies a gnd to a alt relay there to turn the idiot lights on when the alt is NOT putting out.

 

Okay, switched key to ON.
Unplugged voltage regulator plug.
Voltage on the plug is ~0.01V. One wire measured 12.46V to ground, the other measured 11.95V to ground. The battery voltage is about 12.5V
Plugged the plug back in.

Traced it back, unplugged another plug less than a foot away.
Voltage on that plug measured about 0.25V. One prong measured 0.08V relative to ground. The other jumped around between 1.5V and 3V.

All the idiot lights do not come on. Just the relevant ones (brake, door, hatch, etc.).

 

When you pulled the two socket plug off, did the black/white wire have batt voltage on it?

With the alt plug installed, and the key to ON, when you backprobed the WHITE/BLACK wire, did it have 1-3vdc?

 

Is "black/white" a white stripe on a black wire or a black stripe on a white wire? Or you could tell me R/L from the FSM, or top of the "T" / bottom of the "T".

One of the wires did have battery voltage on it when I unplugged it from the alternator. When I plugged it back in and backprobed it, one of the wires did have 1-3VDC.

 

With everything connected up, put your meter on the large output terminal on the alternator. Key off and in your pocket. Do you read battery voltage on it? You should.

With everything connected up, idle the engine. Back probe the white/black wire. Do you have 12-14vdc on that wire now? How much do you have on that wire when the car is idling?

With everything connected up and the car idling, how much voltage is on the large output wire on the alternator? Rev the engine to two grand or so and while at that rpm see what the voltage is on that large output terminal on the alternator

 

Voltage on the alternator positive is slightly lower than battery voltage, regardless of rpm (always ~12V - 12.5V). Same if the car is off or on.

How do I backprobe the black/white wire with the car running? Do I strip some of it bare? Or do I disconnect the connect it leads to (not in the alternator, but another connector nearby). Last time, with the car off, I disconnected another connector that it went to.

Now that I've disconnected the "ROOM" fuse the battery is no longer discharging. It's at 12.5V now, same as yesterday. I used an external charger yesterday to recharge it after it died.

I'll be taking it into a mechanic tomorrow morning. I'll post the cause when I find out, in case others run into the same problem.

 

idk if this would help. but when putting in an s5/fd alternator in an s4 car. you have to wire the battery directly to a wire that comes off the s5 clip. if you do not do so then your battery will always drain when car is off and i dont think it'll charge eather. idk if this helps any. but maybe just check your wires and make sure you have the right alt... silly. i know. but i thought i'd throw it out there

 

The old alternator worked for 2,000 miles before the charging system failed, then worked again. Then when I put in a new alternator it worked again for a little while.

 

Where did I go wrong? You have a series five alternator on the car??????

Room fuse has zippity to do with a series four alternator itself.

****How do I backprobe the black/white wire with the car running?*********8

I said WHITE/BLACK. You can use a paper clip if you don't touch it to gnd. Touch it to gnd and the main fuse will blow or the ENGINE fuse will blow.

Series five?????????????????????????????????????????????? ?????????????????????????????????????????????????? ????????????????????????????

?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ????????????????

And I'm still not sure if you have batt voltage on the black/white wire with the plug off the alt and the key to ON

 

funny this thread started, because i was just in the wisconsin dells and this happend to my car while on vacation. just replaced the alt cuz my old one wasn't putting out what it should have, but did all the rest. i wish i woulda look at this thread b4 all the headaches i went through doing this by myself.

 

You're gonna have to be about 8 times more clear when you write. Hint: add a few more question marks. Did that convey the meaning of the sentances any better? No? Try speaking louder. Oh, you can't do that online? Well, shoot, then I don't know how you're going to explain yourself any better without actually writing everything you want to say... instead of hiding some parts that you assume I know b/c I've fixed charging problems 100 times before. And when I did it 100 times before, it just so happens I used your own personal terminology (not the FSM's, for example). Oh wait, since I did this 100 times before why am I even asking? Nevermind, I know what to do already.

Anyway I'll be taking it into the mechanic tomorrow morning. Would have been today but they were busy. Fortunately I know better than to wait around and waste time guessing. That's why I save money by doing my own maintenance whereas I usually pay for repairs. No sense spending all my free time learning how to do a one time repair. And thanks for suggesting the FSM. I printed a copy to bring along just in case.

 

Really. LIke this question I asked in my first post:

"Pull the small plug off the alternator. Put a meter on the BLACK/WHITE wire with the key to ON. You should have 12vdc. Yes or No?

You NEVER answered that simple question. What was the terminology that you misunderstood? Black? White? Small plug? The "Yes" or the "No"?

From there on it went downhill.

 

I'm not sure if this is the case with RX7 alternators, I haven't yet looked at my FSM to verify it, but lots of manufacturers design the alternator's field circuit to be "excited" by a small current that floats on the charging warning lamp circuit. If the bulb is missing or burns out, the circuit is open to the alt. I have fixed numerous cars that dealers couldn't fix because they tend to forget about this circuit. I always check the indicator lamp first to make sure it comes on with key on/ engine off, then do my voltmeter checks. You might check the FSM to see if this applies.

 

He did say be had the 1-3vdc for the field voltage on the white/black wire. IF he had 12vdc on the Black/White wire, the alternator should have worked when spinning. Once spinning, that same wire would NOW have anything from 12-14 vdc. Closer to 14vdc.

IF this is a series five alternator in a series four,the black/white wire is not used and you have to string a wire to the regulator on the alternator and it has to be a constant 12vdc day and night or the battery will be drained.

He said all the idiot lights DID NOT come on when the key was just to ON and engine not running. They should have come on because on a series four, the white/black wire puts a ground on a relay in the CPU, which in turn powers ALL the idiot light.

BUT, the idiot light cluster is a known failed part as far as cold solder joints on it's jack is concerned so it's not proof positive of a good alternator if all the idiot lights don't come on when the key is turned to ON and engine not running.


To prove the circuit is good b/t the idiot lights and the white/black wire at the alternator , all one has to do is pull the plug off the alternator (only plug on the alternator,hard to miss) and then put a gnd to the white/black wire, and key to ON, then all the idiot lights should come on. IF they don't, then it's probably a cold solder joint at the idiot light clusters jack. Or the same on the CPU's jack. Your choice.

Even if the field is missing, you can rev the engine up over two grand and the alternator WILL put out. Not very well regulated and doomed to failure if so.

The FSM's ENGINE ELECTRICAL has a detailed method of checking out the alternator.

 

Okay mechanic said it was another bad alternator. He applied the proper signal to the regulator plug and it still wouldn't charge. Also said that it wasn't too uncommon for remanufactured alternators to blow after a week. So I'll be getting a refund on the remanufactured alternator after I buy a brand new one. Live and learn. Don't buy remanufactured alternators.

I'll check out the idiot lights after I get the new alt. They used to all go on when I turned the key to "ON". Or I think sometimes they do, sometimes they don't. If they don't I'll reread this thread and/or the FSM as I fiddled with it. I noticed that before the old alt failed it would only charge the battery at 1500rpm or higher. Not at idle.

 

Update: the source for the new alternator kept flaking on me (and btw, while still good, "new" only means more new parts on the reman). My dad had to leave a car at a mechanic, so I drove a 2nd car there so he could get back. I asked the mechanic about an alternator for an RX-7, and he referred me to a local shop. The shop rebuilds the alternators themselves. The building was filled with hundreds of alternators. That seems to be all they do. He gave me a good deal since that mechanic sent me. The replacement seems to be doing well so far, though I just got it. Unlike my last reman, it holds the voltage even when idling with all the electricals turned on (the last one, when it was working, would drop to ~12V at idle under heavy load). He claimed he uses brand new voltage regulators and diodes while a lot of remans don't. He said that's probably what blew.

I'll post again if this alternator blows. Otherwise, if I remember, I'll post again after a few thousand miles. In case I forget to post later, the alternator shop is located on Griffin off of Slater, very close to Gothard and Slater. Huntington Beach, CA.

 

Ok, the new alternator blew from a bad voltage regulator. Took about 7 months and maybe 6000 miles. Shop made me come back on the weekend so they could rebuild it (b/c I work during the week) but then they gave me a replacement instead. No charge. New alternator seems to put out strong power but it's making some noise when cold. I think that might indicate a failing bearing. I may drop by again if I have spare time, or just bring it back if it blows later.

Btw, any store will replace a bad alt they sell if you save the warranty stuff. So while this one lasted longer than my last 2, I'm still kinda disappointed that it blew.

 

double check belt tension too. Too tight of a belt will cause bearing noise, but too loose of a belt will cause slippage.

 

Nah, it's kinda loose actually. About 1/2" of give in the middle. I normally shoot for between 1/4" and 1/2". Checked the tension recently to make sure it didn't loosen any more, and it seemed about the same.

 

There is one common mistake made by mechanics as well as owners when installing an alt, whether new or reman....they forget to make sure the battery is fully charged before startup. When you start an engine with a fresh alt and a partially charged battery, the alt gets hella hot real damn fast. In my 32-year career I've seen dozens of techs install them and forget this very important step. Sure, the alt will work just fine, but with guaranteed shorter life expectancy. Trust me on this. Also, a common misconception is that the alt will fully charge a partially charged battery. The fact is, it will not. It is not designed to. It is intended to run the car's electrical system and to maintain whatever charge is there. Trust me on this too.

 

The most recent alt was making noise as soon as I put it in. I noticed it after I was a little ways away from the shop. It's not that loud, but definitely still noticeable when there's nothing to drown it out. I charged the batteries with an external charger when intalling the last alts, but not this one. Even so the battery was pretty full. I mean if anything the busted regulator would make the voltage too high if I let it.