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Got the '92 all buttoned up after a water pump and timing belt job, but I noticed on the checkout drive that the battery isn't charging. B+ and ground wires check out fine, but there's no 12v at the D+ terminal when the ignition switch is in the 'run' position.
Looks like I have to replace a wire, but I may a different path then the OEM wiring. Does anyone know where the next "upstream" connection for the D+ wire is?
Alternatively, where's the next best place to grab a switched 12v line under the hood?
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Art & runwld, thanks for your input.
This morning's discovery was that a moderately heavy current load (e.g., headlights) dragged the system voltage down to about 11.5 v. Thus the question became, is the battery bad, or is the charging system incapable of delivering enough current to handle the load? Without additional testing, I couldn't tell. My 2-year old Wal-Mart battery at rest and disconnected showed about 75% charge (12.35 v) and would charge up higher on the charger, but within a day it would drop back down to 12.35. In my mind I envisioned that a failed diode in the rectifier bridge would limit the alternator output but still provide some current... still not sure if that's true. BTW, belts are tight & good.
Stopped by the local AutoZone on the way home tonight and let them test the system. I correctly predicted what would happen, which is that if the battery was below about 12.7 v they wouldn't be able to load test the system... and so I came home with a new battery. The story concludes with a happy ending (other than buying a new battery) - new battery installed, I can turn on every electrical load the car has and still be close to 14 V. I'm happier to replace the battery and not the 100A alternator I put in a couple of years ago.
Just one more odd battery failure to add to the list. The fact that it happened right after the t-belt and water pump replacements had me adding the alternator to the list of suspects.
Thanks again, gents.
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Hope this is the case, but my experience goes against it. The alternator should make enough electricity to run all your lights and accessories, without any assistance from the battery. About the only battery fault that could prevent this is a shorted cell, which should have alerted you by nose if by no other sense, as the remaining 5 cells spewed gas from overcharging.
However, replacing a battery with a fully charged one, will offer the assistance needed to an alternator with a slipping drive. Time will tell, and not enough of that has passed yet.
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Art Benstein near Baltimore
If you keep your feet firmly on the ground, you’ll have trouble putting on your pants.
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Art, the pieces are fitting together... a shorted cell makes sense. Over the Chrstmas break I noticed a few cells in the battery were low on fluid, then just last week when I was sniffing around for a coolant leak I saw the top of the batery cell covers looked like they were sweating.
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Smitty, if you're talking about a 740 or a 940, I hear that can involve some flexible circuit board traces in the instrument cluster.
If it is a 240 perchance, there's a flex fuse on the back of the cluster, but you'd have more symptoms than just the lack of exciter voltage.
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Art Benstein near Baltimore
"If people don't want to come out to the ball park, nobody's gonna stop 'em."
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Art, thanks... I hope you had that on hand and didn't draw it out just for my benefit!
Right now I'm not sure what's going on. After I posted last night, I re-checked my work and I did get power at the D+ line, but the system wouldn't charge over 12.3 V.
I did some experiments this morning and now I find if I leave the headlights off, the system charges as normal. I did some significant rewiring last year when I installed e-code headlights, and some of that may have been disturbed during the weekend festivities. I'll dig into that tonight... for now, I think the charging system is OK.
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I don't think it was your question that triggered the drawing. More like one that broke the camel's back in Feb two years ago. There surely are a lot of misunderstandings regarding this electrical power plant. I tried to cover the whole 19 years, or at least those without Sev/Motorola/Marchal and external reg's.
What I could not tell from your post is where/how you were checking for D+ voltage. Backprobing connected or disconnected, key on, motor running, etc. But then I couldn't tell what model car you were working on either until I spotted your dupe.
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Art Benstein near Baltimore
Why do supermarkets make the sick walk all the way to the back of the store to get their prescriptions while healthy people can buy cigarettes at the front.
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My question would be, are the headlights shorted somehow (unlikely if they work normally), or is the charging system so weak that their current draw is overwhelming the alternator.
I'd see if I could duplicate the low charging voltage by leaving the headlights off, put putting everything else on, window defogger, fan on full and check the charging voltage.
I might even take some old, other, headlights and make a "load" with them to test the charging system.
If the alternator is unable to put out full power (amps), take a look at the brushes, or then it could be a bad diode, (and check the belt tightness)..
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84 242Ti IPD bars&springs, 89 745 16v M46 IPD bars, 89 744 16v M46 IPD bars, 93 945 Turbo AW71, 91 245SE AW70 IPD bars, 93 245 CLassic M47
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...(and check the belt tightness)..
Amen. The pulley can slip under load without speaking in the range of human hearing. Same with the harmonic crank pulley balancing vibration damping thingie.
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Art Benstein near Baltimore
"Never answer an anonymous letter."
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