944 charging issue. Diodes?

[m.w.oldham]

Hi,
My '84 944 has had a problem with the battery holding charge for a few years now. When it starts, it runs fine for as long as I drive with no battery light indicator coming on, but if left parked for short periods of time with just the fog or interior light on, the battery is dead by the time I return. Left alone for a week with nothing on will also drain the battery. Problem seems to be getting worse.
The alternator seems to charge (voltmeter agrees), as the car would otherwise die somewhere between here and the 200 mile trip I take in it. The battery is fairly new, and did not fix the problem a while ago when I replaced it. I am told by a shop (that I have no faith in; they screwed up a few other things while trying to sell me things I didn't need, and tried to blame it on me http://forums.pelicanparts.com/ultimate/mad.gif) that it's the diodes. Does this sound right?, and if so, can I replace the diodes without replacing the whole alternator?
Thanks for any help.

[drew1]

Well, get an ampmeter or VOM . Pull the hot wire from the alternator & measure the current between the wire & alternator terminal. If you are pulling a couple hundred milliamps something may be wrong. But before I went decided on this I would put the wire back on & pull the Pos terminal on battery & measure current between it & post. If you have a lot, start pulling fuses &/or relays till you see a drop.

Note: Some relays are kind of hinden on the hump instead of relay panel.

[MrWrong]

This sounds more like a parasitic load and a bad battery to me.

I'd start by disconnecting ground cable from the negative terminal on the battery and charge it overnight.


Then with the key off I'd place some sort of ammeter between the negative terminal and the ground cable. Off the top of my head you should get a reading below 50 mA or 0.05 A. If you get a larger reading you probably have a parasitic draw which is some device drawing power from the battery when the key is off, this is bad.



I'd then take battery to a local auto parts store and have them load test it, several around here will do it for free. It sounds to me like you unknowingly let the battery go completely dead once or twice from the parasitic load. Most batteries don't recover too well from this.

[bearone2]

does the alternator light come on when the key is turned but car not started?

if left on the interior light will pull the batt down and the alternator won't fully charge the batt, it must be charged.

as in post #3, the batt may be dead.

[m.w.oldham]

The alternator light does come on when the key is turned, but engine not started. The light quickly goes out when engine starts. When I have a lot of electric running (lights, stereo and amps(2), fog lights, etc...) the light does start to glow.
The battery was load tested a while ago and it was ok. My meter bit the dust a couple weeks ago, so I'll have to find another way to get my numbers.
bearone2 says..."if left on the interior light will pull the batt down and the alternator won't fully charge the batt, it must be charged."
Shouldn't the alternator fully charge the battery even if it goes from completely dead and needing to be jump started. The car has been jump started many times in the last year or two, and it normally returns to its semi-reliable state after driving it for fifteen to twenty minutes.

[bearone2]

it's working right, that's how you know if you have a failure/running too much stuff, when the light comes on or is dim.

nope the alternator won't bring it all the way back and the alternator is working overtime at a high charging rate to run everything, which can shorten it's life.

the fuel pump draws about 5a, add lights, fogs, 2 amps, a/c, it all adds up.

overnite, a fully charged batt should show 12.5-12.6v, if it doesn't, it's not fully charged.

years ago my lights got dim driving to work in the 84na and the batt died.
the light wasn't coming on with the key and the light was in series, like xmas trees and the batt wasn't being charged.

in later models the bulb isn't as critical.

i pulled out the cluster, changed the bulb and now the light was on with the key and went out when started.
i'd had the same thing on a volvo years before with a bad alternator light bulb.

[Lapponia]

++1. Jump starting many times in the past should have arlarmed you that something isnīt in order. Your -84 like mine has an transitorized charging "relay" at the back of the alternator. Using a lamp current to energize alternator is history and it is not used here as the electronics in the charging "relay" takes care of it nowdays. Most likely you got a faulty "relay", probably worn brushes not in contact with the two rotor rings. What you get is a near normal voltage but too a low charging current as the rotor is energized by residual magnetism only. Remove the regulator from behind the alternator and check the brushes. A new regulator is not expensive and could be the remedy here.
I second to the opinion that battery could be bad cause the many bottom discharging events that happend to it. Good luck
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Lapponia 1984 944 na

[Lapponia]

bearone2! My volvo 140 -70 and 240 -78 had Bosch alternators that was excited by a bulb in the dashboard. The charging relay (electromechanical) sat separately in the engine bay. Worn brushes gave a flickering light in that bulb and a hint to change them. Iīm sure that these were the first design of a 3-phase winded alternator with rectifier/diodes to make DC current for battery and electrical equipment. Later alternators has become more reliable i think.
______________________________________________-
Lapponia 1984 944 na

[HondaDustR]

The alternator on the early 944's are definitely excited through the charge bulb. There's no charging relay. Just +12v from the ignition switch to the bulb in the dash and out to the D+ terminal on the alternator. The bulb should light brightly if you disconnect the small blue wire from the alternator and ground it out with the key turned on.

[curveto]

The alternator light does come on when the key is turned, but engine not started. The light quickly goes out when engine starts. When I have a lot of electric running (lights, stereo and amps(2), fog lights, etc...) the light does start to glow.

You have the EXACT same symptom (and probably condition) I had in my 944. Took two years and ten minutes to figure it out. You may be having (or will have) other related symptoms. See if any of these seem to fit the bill...

This is going to be long (just because I'm gonna be thorough)

Every so often (seemingly randomly) the car will act like you have a problem with the fuel system. I encountered fuel starvation like symptoms, rich running symptoms (black smoke), a brief but persistent stumble passing through 2800rpm.

I also (like you) went through multiple batteries (slowly they loose it, not because of parasitic loss but rather something else ... read on).

The only "common" theme was that the alternator light would glow (VERY faintly) when under heavy load (all lights on, etc.) ... again, only some times. Usually not when one of the other symptoms was in play, either.

Other common symptoms (that I didn't associated with a common cause) include faint dash lights, faint headlights (neither too bad, just not "brilliant").

Once, on a trip between Phoenix and LA the car faulted badly (would not hold freeway speed) but when I got to the end of the off ramp she idled like a champ. I was like WTF?!? Thought I was completely screwed (3 hours from anything but scorpions in both directions). It fixed itself. Then broke. Then fixed itself, etc.

Then, I was autocrossing and it faulted during a run. EVERYONE that looked at the car at the autocross thought the fuel pump had plugged or similar.

The bouts were random at first, always magically healing itself with a little time or (now I know) temperature change. It finally became persistent enough that my mechanic "knew" that the tests they were doing weren't identifying the problem.

Over the years I did the following (now known irrelevant) things:

0) Numerous tunes;
1) Changed the 02 sensor;
2) Changed the fuel filter;
3) Change the battery (multiple times);
4) Changed the alternator (that broke for unrelated reasons);
5) Belts, of course;
6) Changed the blinker/wiper/cruise control, umm... block;
7) Swapped out the ECU (not permanently .. he let me keep it for about a month ... still happened).

The problem was that the main line that runs between the voltage regulator and battery (embedded inside one of the main harnesses that feeds a bunch of the engine) was old/weak enough that it wasn't passing useful current to the battery. The fuel controller (and a bunch of other stuff) was browning out. Your mechanic can easily test for this *if* the car is misbehaving. If not it can be harder to diagnose.
The fix is:

a) replace a fairly expensive wiring harness;
b) run a bypass line.

I chose option #2. It wasn't expensive. They dressed it in nice. An automotive single heart bypass, if you will.

The car has been PERFECT ever since. Bright lights, no stumble at 2800rpm, no FI problems, no alternator glow (and it's VERY light, that glow ... isn't it?). PERFECT!

You're symptom sounds EXACTLY like some of mine.

PS - I was almost ready to flush my 944 because I never knew when the FI was going to go all wonky.