AreExSevenProject

iTrader: (1)

I have a streetported 1987 rx7. It has cone filter, port, exhaust, a/f guages, fog lights...etc. The problem is that it shows about 12-13 volts at idle, and when the rpm's climb it sometimes climbs but other times does not. I took the battery in and they said it had 98 percent life (even though its been thrashed, and had its warrenty). So I believe the alternator is the culprit. So i was wondering the easiest way to diasnose the indivual problem on the alternator because I would like to fix it myself (i.e. bearing stator....)

Thanks, Phil.

jackhild59

iTrader: (7)

It is likely that your alternator is working as designed.

The S4 alternator is pretty low output by modern standards at 70 amps. The S5 was 'upgraded' to 80 amps.

You could upgrade to an FD alternator- or you could buy a custom built alternator.
Before you go to all that trouble, you should verify all connections and grounds are clean, corrosion free and tight.

Good Luck!

HAILERS

You might help yourself by looking at the voltage AT the alternator with a digital meter and not rely on the factory gauge.

w0ppe

I've got the same problem but the alternator isn't really the culprit (I've tried several and they tested OK anyway).
Now, my problem as said before, it's a bad ground and connection within the vehicle somewhere. Mine has several (found things falling off and rusting off etc. etc.). Not fully done yet but I would check the wiring if your alt + batt are good.

AreExSevenProject

iTrader: (1)

I have a professional multi meter and a battery tester. I check both the battery voltage and the alt voltage and they fluxuated and I wrote down the approx. voltage.

AreExSevenProject

iTrader: (1)

okay well I disconnected the negative terminal and hooked a tester light and it shows no shorts which is good. So tommorow I will check all grounds and connections. I can get a free alt. though so I may plug that one in just to see if it fixes the problem.

HAILERS

Someday you might want to install new brushes in the alt. It's pretty straight fwd if you follow the FSM Electrical section. You don't have to remove the front pulley to do it. The new brush assy cost approx 50 bucks from AutoZone.

If you read 14-14.5vdc at the alternator, that's good. If you read quite a bit less at the bolts that hold the Main Fuse in, that's not good, so you could clean those two connections to make better contact.

The way it works is, the output of the alt feeds the Main Fuse , which in turn feeds the battery and the engine bay fuse box. Plus the same line off the alternator feeds the ignition switch itself.

That is fairly important, since the ignition switch feeds two of the busses on the interior fuse box. So corruption in the ignition switch can cause problems or the feed line to the switch can cause problems.

That said, the ECU isn't fed from the interior fuse box but from the EGI fuses in the engine bay, so that's why you make sure the voltage on both sides of the Main Fuse is the same as the output of the alternator.

Or you can start the engine up. Put the pos lead on the output of the alt and the neg lead on the Case of the alternator. Put it on A/C volts and rev to around three grand with the headlights on. The A/C shouldn't be over a half volt when you do that. Actually should be a lot lower. That gives you a clue if the diodes are good/bad.

Or with engine off and the wire off the output terminal, put the meter on diode check. Pos on the output stud and the neg on the case. The reading should be under .9v.......if memory serves. Read that somewhere, forgot where right now.

EDIT: Try this site http://www.aa1car.com/library/charging_checks.htm and do some of it like the Voltage Drop checks etc. There's lots of *stuff* out there on the internet you can try.

HAILERS

EDIT: I got the leads wrong on the Diode check. Follow the attached jpg on that post for the right way.

This article is fairly comprehensive: http://www.forparts.com/techtips/electric_diode.asp it also explains the L terminals role in life fairly well. And do the voltage drop test as described about half way down the page.

The second paragraph in this article: http://www.pelicanparts.com/techarti...oubleshoot.htm explains why, when you leave the small plug off the back of the alternator, the alternator will work if you rev faily high. Like two or three grand. It won't be regulated volgage if you leave the plug off the back and you can expect alt failure in the future if you leave that plug off. Just wanted to point out WHY the alternator CAN output with no volage to its regulator.

As far as grounds go, check the battery neg terminal itself, then where the negative cable grounds below the left strut tower and lastly where that cable attached to the long bolt that holds the starter to the transmision/engine. That's about it for grounds as far as I'm concerned....when it comes to the battery and the alternator. Well, the alternator gets its gnd from its attachment to the engine, so that counts also. But you've two bolts doing that and that's unlikely to be the problem or a problem.

AreExSevenProject

iTrader: (1)

Okay the alternator has been acting wierd. Sometimes it charges very well at around 14-15 and then other days it goes way lower. So tommorow im going to check connections and hopefully work out a couple bugs before getting a S5 alt (<---hopefully...dont want a 70 amp S4)

HAILERS

Get a meter out and a sewing needle. Turn the key to ON, engine OFF. ***** the WHITE/BLACK wire with the sewing needle. Then put the meters neg lead on a known ground and the positive on the needle. The meter should read 1-3vdc.

That's from the ENGINE ELECTRICAL section of the manual and verifys the field excitation.

HAILERS

If a series FOUR alt does not show 1-3vdc on the WHITE/BLACK wire at the back of the alternator, WITH the small plug attached to the alternator, then the field in the alt won't get excited and the thing won't put out.

If it turns out that 1-3volts is missing, go look at your Warning Light assy with the key ON and engine OFF. All the warning lights should be on. When an alternator is not putting out, it sends a ground signal to the alt relay in the CPU, which in turn puts a gnd on the Warning Light Assy and that results in all the warning lights coming on.

Sometimes all the Warning lights won't come on, just a select few light BRAKE or HATCH. It could be that the Warning Light assy has what are called cold solder joints where the elect plug attaches to the assy. ONe way to prove that this is the poblem, is to pull the top plug off the CPU. Then extract the Yellow/Blue wire out of the plug and put the plug back on the CPU.

Now ground that Yellow/Blue wire to a known ground. How you do that is up to you. Then turn the key to ON, engine OFF. All the warning lights should be ON. If they are all ON, then the Warning Light Assy is good and the problem is b/t the small plug on the Alt to the CPU.

Instead of extracting the wire above, you could put a wire in the back of the yellow/blue wire. It'd have to be a thin wire to do that, and grounded at it's other end. Then you'd just turn the key ON, engine OFF and see if the Warning Lights come on.

So say they did all come on when you grounded the yellow/blue. So if that's the case, go to the small plug for the alternator. Pull it off. With a piece of wire, ground the WHITE/BLACK wire. When that happens, and the key is to ON, engine OFF, you should hear a click from the alt relay inside the CPU AND all the WArning lights should come on. That would prove the wiring b/t the alt plug and Warning Light assy is all good. Might do that first before the other things mentioned above.

Another thing about series four alternators. IF the excitation voltage does not show up a the white/black wire, the alternator won't put out. BUT if you rev the engine high, it will start putting out thru the residual magnatism in the rotor assy. Then the field will be fed by the diode inside the alternator that is spliced to the field wiring. So if your isn't putting out sometimes, rev the engine and see if it now starts to put out. IF that happens, do what I mentioned a few post ago, check the white/black wire for 1-3volts.

HAILERS

There's lots of STUFF you can do with a meter and the alternator. Idle the engine and put the positive lead on the large output post of the alternator. Then put the negative lead to the case of the alternator. Write down the voltage. Now leave the positive lead where it is and put the negative lead on the battery neg post.

Compare both readings. It's likely the alt B to alt case reads higer than alt B to batt neg post. IF so, then it's possible the alternator case isn't grounded to the engine very well. Pull the adjustment bracket all the way off. Sand both sides of the bracket where it attaches to the engine and sand both sides of the slot where the adjustment bolt goes. Reassy everything and chek again. Most likely both reading will now be closer to each other.

I had that problem. Read in the low 14's from alt B to the alt case, but read 13.8 from the alt B post to the batt neg post. Cleaned the adjustment bracket on both sides and now the 13.8 is in the low 14's.

I'm listening to CAstors little brother on C-SPAN. You know Cuba, the People's Paradise where this year for the first time, your allowed to buy cell phones at a hundred bucks................but you only make 20 bucks a Month. But hey, free health care........just like and inmate in Levenworth or Huntsville.

AreExSevenProject

iTrader: (1)

Very good information. I will perform these tests before I put in the S5. I got it today finally (and lost my credit card getting the money for it...woohoo). So I will do all of the mentioned test before putting the new alt in to ensure the alternator is working properly. Time for a S5 alt. swap...woohoo. Thanks Hailers. Ill post any troubles after the swap (or before)

AreExSevenProject

iTrader: (1)

Pu in the S5 alt today. It was a pretty easy swap and I branched the constant (new) wire off the EGI fuse. The batt is now at 14.3 started up and the alt (b terminal) is at 14.3...and etc...all are at 14.3.

I still have a slight short in my fogs and dash lights (wired seperately) and im able to disconnected them from the battery so it does not run it down. But When I turn everything on the voltage (inside meter, couldnt test becaus I was drving) now drops to a little above the 12 mark. But when everything is mostly off (except stereo and air fuel guage) it reads about the 14 volt mark. Is their something I can do to fix this, or is it normal? Also What should I do to fix the short for the dash and fog lights...(already soldered everything up)