GoodfellaFD3S

iTrader: (213)

Very odd problem---my car seems to fluctuate between two different "modes" with no rhyme or reason to it.

(1) Car idles fairly smoothly, at the proper 950 rpm, and battery voltage is 13.5-14.0 volts.

(2) Idle constantly fluctuates between 1500 and 1000 rpm, battery voltage is 11.5-12.0 volts.

Also, under (2), whenever I give any throttle to accelerate, the Valentine One goes nuts and immmediately starts giving me a 'Laser' warning. I think this is related to the lower battery voltage.

I checked my battery connections, as well as the tension on my alternator belt and poked around under the hood and all seems fine.

I am thinking that my alternator may be having problems with it's voltage regulator.

Any comments, insight, suggestions are welcome .

DaleClark

iTrader: (55)

I would suspect the alternator is not feeling well, or the main power wire to the alternator is making a flaky connection. When the voltage drops like that, it's indicitive of the alternator not putting out the juice or some sort of sudden load on the charging system.

Might be worth pulling the alternator and taking it to a local alternator shop - they can do a full once-over on it pretty cheap or free.

Haven't studied the FD wiring diagrams too much, but I redid the whole starting/charging harness on my FC. The alternator main wire on the FC went from the battery terminal to the "big" fuse in the fuseblock, then on to the alternator itself. I replaced it with 4 gauge wire - nothing like overkill . Anyhow, the power wire bolts to the fuse itself and that connection can in theory come loose and cause similar problems. I think, on the FD, that the main fuse block that hangs off the positive battery post would contain the power wire to the alternator and the fuse for the connection.

Hope this helps!
Dale

GoodfellaFD3S

iTrader: (213)

Used a mil-spec Oscilloscope and it turns out that the voltage regulator is toast as I had thought. I was seeing spike as high as 8.5 volts, which is insane on a 12 volt system.

suganuma

Awesome. I've been having electrical problems also. I'm hoping to get time tomorrow to pop start the car, drive to the hobby shop, and pay money to work on my car and diagnose. :/

My paint is starting to look like Alan's in this ridiculous place.....

GoodfellaFD3S

iTrader: (213)

that sucks man . Well, Martin's paint shop is painting my vert as we speak and my FD looks like a million bucks. At least you know where you can take it......

J.S.J

The ECU will default a to a higher idle speed if the system voltage falls below normal ranges. I would also think the ABS light would come on as well. I am assuming the ABS voltage threshold is tighter as it is with most systems.
I would concentrate on the alternator and its support wiring.

GoodfellaFD3S

iTrader: (213)

Used a mil-spec Oscilloscope and it turns out that the voltage regulator is toast as I had thought. I was seeing spike as high as 8.5 volts, which is insane on a 12 volt system.

RotaryResurrection

iTrader: (8)

I've seen fucked up batteries cause problems like this as well. I had put a brand new one in my FD in January when I put her on the road, but the bodyshop guy apparently killed it when he did the paint work in april. IT held charge, but cranked really slow afterwards, and kept getting weaker and weaker. Finally the car would just start bucking like a mother at 70mph, and hitting the brakes would cause the car to die due to the voltage drain, and the aforementioned valentine one spasmic fit to occur as well. A new battery solved all of it. Just an idea.

trancemaster

I found out that I have this problem too. How much do FD alternators go for?

RotaryResurrection

iTrader: (8)

PM silverrotor on this forum. He sells us FC guys the FD alt's as an upgrade for ~$200 us or a hair under. They are new units btw.

DamonB

First thing to check is the voltage regulator, they can get noisy when failing.

*oops, you already did that

GoodfellaFD3S

iTrader: (213)

Installed the new alternator, and all the problems are gone .

idles smooth, voltage is good, car drive much more smoothly, esp at part throttle and when initially getting on and off the throttle.

All those on their original alternator might want to think about replacing it. Mine had already been rebuilt once and I still had these problems. I decided to get a remanufactured one from Mazda, and hopefully this will last longer.....

Rich

trancemaster

nice rich, i hope when ii replace mine i will get the same results.

- Art

GoodfellaFD3S

iTrader: (213)

Thought I'd update this thread in case anyone else ever has the same thing happen.

After killing one alternator and one ignition amp (jacobs), I found the source of the problem----my damn positive battery connection was loose! Talk about an expensive kick in the nuts.

This was all three years ago, but I was searching and dug this up

jsplit

Funny, my Escort radar does that now.
7 out of 10 times when I accelerate hard it throws laser.
Unfortunately it does the same thing in my M3 :\

FD3S2005

iTrader: (11)

wow... how do you find that out now that it was the battery and how can you say for sure?

GoodfellaFD3S

iTrader: (213)

I found out a few years ago, just never updated the thread. I have my battery in the back hatch, with some car audio style connectors that have the cables mount from underneath. Because of the mounting method, it wasnt easily visible that there was a problem until I starting probing around the battery and wiring.

I can say that for sure because I had voltage problems with two different alternators, and upon tightening all connections the problem was solved