vipernicus42

iTrader: (4)

Hey Guys,

So here's what's happening:

A few weeks ago I was just driving, then everything died. I made a post about it back then because it did some damage. It blew the main fusible, but not before taking out my fuel pump relay, main "engine" fuse in the fuse box and all my gauges except the speedo and tach.

So I replaced the burnt fuses and fusibles, swapped a jumper wire in for the fuel pump relay and replaced the ignitors which I had suspected were blown. I started the car and it ran, which was great. What I didn't realize was that my alternator was blown. I drove the car for a while with the alt only putting out about 11v. Eventually it got to the point where I didn't have enough power for *anything* except to limp the car forward at just-above-idle speeds, mis-firing frequently. I got the car home like that and sent the alternator out to be rebuilt

I put the rebuilt alternator on today and got the car started. I managed to make a run to the bank and the gas station with the car driving normally (minus the gauges) but then I was taking off from a green light and it happened again. This time the main fusible didn't go, but the car lost power in a big way. It was still able to idle, and I could kind of limp it forward at 20kph but it shook violently because of mis-firing and there wasn't enough power for the lights or anything.

I pulled it over, and with it running I had 12.3v across my battery terminals where just 10 minutes ago I was showing 14. I managed to limp the car home, but I suspect that I've blown another alternator. It's not producing enough voltage to run the car properly, and with the battery still mainly dead from the last time, when the alt went the car lost power right away instead of letting me drive 10-15km before "dying".

Any ideas as to what can cause this?

For information, I installed my FD alt two or three years ago. The only problem it ever developed was a problem with the "rectifier" which caused the battery to slowly drain over a period of a few days when the car was not running. This spring, I got the alternator rebuilt to fix that problem and it ran all summer just fine, until two weeks ago when it blew. So I don't suspect it 's a problem with they way I originally wired it up or anything, but it obviously could be a problem that has since developed somewhere in either the wiring I did to install it or somewhere else.


I'd appreciate any help you guys could give that would lead me in the right direction.

Jon

680RWHP12A

check your grounds. if there is alot of resistance where the grounds connect , this will cause many problems.. use an ohm meter and check the resistance first at the batt terminal so you get an idea of what low resistance is, then check the batt terminals, and all other ground terminals and compare resistance levels.
also make sure you have a thick positive cable going from the alt to the battery. at least a 8 guage wire

Re-Speed.com

iTrader: (3)

+1 for checking your grounds.

Kentetsu

I'll also say grounds. But having said that, you've also described the symptoms of a blown apex seal ("was still able to idle, and I could kind of limp it forward at 20kph but it shook violently").

This is a little confusing to me because if you lost the alternator, then you should at least have had sufficient power to run the car for a while. But you state that it was an immediate reaction. But now that I consider it, an intermittent grounding issue could explain it if it were a situation where at some points you completely lost your grounding. If the engine isn't grounded, then its really tough to make sparks. So maybe your alternator is fine, but your ground cable is very loose or very corroded.... I'll be interested in your findings Jon. Good luck.



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vipernicus42

iTrader: (4)

Well when I let off the gas it would idle fine, but ask it to give you enough sparks for more than 700 rpm and it suffered horribly.

My grounds are all good (at least the main ones I know about to the strut tower and the bellhousing), and my battery cables were replaced with thicker-than-stock copper-core cables that I made a few years ago.

My guess is that the reason the reaction was near-instant because the battery was still completely dead from the earlier alternator issues. If the battery had been fully charged I'm sure I could have driven quite a while before feeling the effects, as I did the first time.

Assuming that this latest incident and the first incident were the same (something causing the alternator to die) what could cause that other than bad grounds? And doesn't the alternator ground itself through its casing anyway?

Jon

RXnos1200

iTrader: (24)

Have the battery load tested. May have some internal issues with the battery. You might have 12V with a volt meter at the battery but you need to see how it reacts when you have a load on it. Just something I would check if you haven't done it already.

DivinDriver

iTrader: (15)

A high-current short somewhere can kill an alternator, and would also explain the blown fuses. Make sure your battery isn't loose and touching the body, and look for frayed wiring or pinched wires that can short to ground.

Bad ground is definitely also possible, but it takes a LOT of current to blow the fusibles. Hard to invision a bad ground doing that, unless it was making current leak backwards thru the system.

vipernicus42

iTrader: (4)

After a VERY lengthy discussion with the alternator rebuild guy (who is extremely knowledgeable and a really nice guy. He only did the second rebuild, the first was done in a city 6hrs away) we came up with some ideas. One thing is for sure, while I did wire up the FD alt *correctly* 2yrs ago when I installed it, the wiring I used was much too small.

The stock FB alternator doesn't have a "sense" wire to tell it how much to charge the battery. It senses off its main wire (I believe) and instead it just has a relay inside it that controls whether its voltage regulator is on or not. This R Terminal takes a switched 12v source from the ignition, and the other two terminals take Dash lights and main.

The FD alternator however doesn't behave like that. It has a "sense" wire that needs to see battery voltage at all times and has no use for the "Switched" wire the FB one had. So this S terminal needed a new wire run to the battery side of my main fuse, and the switched wire originally going to the R terminal on the FB alt was just cut and taped off. The other two terminals were still dash and main.

So when I installed my FD one, I ran a wire to the battery side of my engine bay fuse block for the "sense" wire but I used something tiny, like 20-22awg, thinking that it didn't need much since it wasn't carrying current, just sensing.

Turns out I should have used nothing smaller than 16awg, preferably 14. I was right about it not carrying current, but it can't sense all that well over 20awg and you're just asking for trouble if something happens to break that tiny wire.

I didn't upgrade the main charge wire for the alt either. the stock one is puny compared to what I should be using for the FD alt (I should use 8awg or larger, probably a 6awg would be good, the stock is like 12 or something)

Our theory is that my "sense" wire broke inside somewhere causing the alt to go into "full charge" mode constantly, but since my main wire can't take a full charge from that alternator, things went to hell in a handbasket.

Or something similar anyway. So it's getting its voltage reg replaced *again* and I'm going to completely replace the "Sense" wire for the S terminal of the FD alt with a 14awg wire to the positive side of my fusible link box, and replace the B terminal wire with a brand new one that's 6awg.

HOPEFULLY that will stop me from blowing the alt again. If the problem is actually elsewhere in the system, the only way I'll know is if this alt blows again within a day of me installing it with the new wiring. Then I'm back at square one trying to figure out what went wrong. At least I know my battery cables are good. I'm going to clean off the contacts where the negative wire attaches to the strut tower and bellhousing, and make sure it's attached properly at the starter and the fusible link box, so then that just leaves the rest of the car's entire electrical system to deal with.

Jon

vipernicus42

iTrader: (4)

For anyone looking for the information, here's the information that's in the archives on the alt swap. All original FB alts are like the "S4" alt, and the FD alt is like the "S5" one. So the information is identical when swapping from FB to FD alts as it is when second gen guys swap between S4 and S5 alts.

I added some text to the image to help folks out.

DivinDriver

iTrader: (15)

So, B=Battery, L=Load, and S=Sense?

vipernicus42

iTrader: (4)

Well no, L isn't Load, it's "Light"

L is the Dash light that tells you if your alt belt snaps. For all generations, L goes to the dash warning light / oscillator wiring somehow.

and R=Relay for Regulator

So:

B = Battery (usually through main fuse on the engine bay fuse box with a split off to power the ignition)
S = Sense (usually connected to the battery through another fuse in the engine bay fuse box)
L = Light (goes inside the car to somehow hook into the warning light system, possibly with oscillator)

R = Relay/Regulator (comes from the switched ignition positive, ignition on = 12v+, ignition off = 0v, from fuse box inside)


And whichever alt you have it has either an S terminal OR it has an R terminal, and that difference is what's important.

Jon

vipernicus42

iTrader: (4)

I downloaded the FSMs for the 85, 88, 91 and 94 Rx7s and made these diagrams for the Alternator Connectors.

Now everyone has a reference for which wire does what on which wiring harness for which alt.


As you can see, the S2-S3 alts have an "Ignition" power wire while the S5 and S6+ Alts have a "Direct-to-battery" wire instead


For myself, I'll be running my new 6 gauge wire from the "B" terminal on the alt to the main fusible link which I will upgrade to 100amp. I will splice the stock white/red wire going to the ignition into that wire there.

Then I'm going to run a 14 gauge wire from the "S" terminal on my alt to a spare spot I have in my fusible box (which is off a 2nd gen) and use a 40amp fuse so that the sense wire gets directly connected to the battery positive through that fuse.

Dash wire stays the same.

THAT should solve my alt wiring issues.










Jon

vipernicus42

iTrader: (4)

And as usual with Jon, when something goes wrong with his car, he goes completely overboard figuring it out and making SURE it doesn't freaking happen again!

And as unusual with Jon, he's currently typing in the third person. He should really get that checked.

Jon

Kentetsu

Kentetsu thinks that Jon should consider getting this information into the Archives. Maybe even as an "add on" to the original instructions on how to make this swap.