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As Art suspected it could, and it has, my charging problem is back! Makes sense since I never found the cause, it had just started working normally.
Currently, with key on and engine not started, The cluster idiot lamps all glow normal brightness. When engine starts, the battery, parking, brake failure, and bulb failure all glow dimly and voltage from the alternator is below normal battery voltage.
If I connect from D+ wire through 12v test bulb to D+ terminal on alternator, the bulb doesn't glow. When I test current through this same test circuit, it's pulling only 120mA.
If I connect the 12v bulb from B+ to D+, the bulb glows until I start the engine, then the alternator charges normally. If I disconnect the D+ wire after a few seconds, the alternator continues to charge normally.
I have removed every ground connection in the engine bay, cleaned and tightened. They actually all looked shiny and clean already. (This car has never seen snow).
I assume my problem is still in the cluster. I traced everything and checked all points for resistance last time. Ideas as how to proceed?
Thanks so much!
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Hi Build,
Your problem looks like a funky D+ to me.
Measure D+ at the alternator with the meter ground at the battery anode,
(not to be confused with the battery cable clamp) with the ignition switch in the run position. Since you can have a ratty ground anywhere, it's best to get the meter grounded to the negative battery anode.
Measure again with the car running.
If D+ goes west when running, one possibility is a loose series connector A
pin 19 red wire to your instrument cluster. Look at it carefully and compare to the other pins.
What's your email? I'll send you the 240 Volvo charging service manual.
It has a nice fault tracing section.
Bill
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Hi Bill,
At engine stop, it has 12.6vdc to D+ to battery anode. When the engine is running and cold, d+ has 14.3vdc and it charges. After 5-10 minutes, or sometimes 1-2 minutes, it stops charging, at that point there's varying voltages at d+, anywhere from 1-9vdc. When I disconnect the d+ wire, there's full battery voltage 12.6vdc from it to battery negative anode.
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Why did you disconnect the D+ ? It has to behave in the circuit.
A loose connector or connection may not misbehave with no load.
Did you look at Pin 19 and see if it's loose?
Are you able to make the D+ measurements on either side of Connector A Pin 19?
(without unplugging it)
Put a shiny new charging lamp in the socket for good luck.
Look around the instrument cluster traces for the D+ circuit for cold solder joints to and from the connectors and charging lamp socket.
Don't you want the Volvo service manual for charging?
It will tell you how to fault trace your problem.
Bill
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Hey Bill,
Yes, I'd love to have the manual. Thanks!
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Hi ___,
What's your e-mail address?
Bill
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I put this picture in your Turbobricks thread because I never really got the warm fuzzy feeling you replaced it.
Hope that's it. Lot's cheaper and easier than a new alt and it lines up with the symptoms and work you did under the hood.
--
Art Benstein near Baltimore
"The third derivative is completely useless and its a felony to make jokes about them at the airport. Just stay away from them. Even the chocolate ones." -Kenn Amdahl
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Hey Art, thanks for that. When I checked the ground wire it looks good and does test for continuity. I even connected a heavy jumper cable from the frame and battery negative directly to the alternator case. I also checked for current and voltage from alt case to ground. This one has me stumped.
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But I will say that from the alternator case to battery negative terminal, there's 18 ohms of resistance. Does this seem a little high?
I've checked and cleaned all engine bay ground connections, unless there are some that are very hidden. I followed an online 240 article about the ground locations.
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Do you get the same 18ohms if you meter from the battery neg to any other parts of the engine, the head or block for example?
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Hi Derek UK,
I get 17-18 ohms from engine to battery negative. 16-17 ohms from firewall to battery negative.
When I connect the alternator case directly to the battery negative with heavy jumper cable, there's no charging.
When I jumper B+ to D+ it starts charging with a reading of 14.21vdc on B+ and 14.3 on D+, and 14.09vdc at battery. After running 5-10 minutes it stops charging, and D+ voltage reading varies afterwards. If I then jumper B+ to D+ again, it doesn't start charging again until the engine has cooled. It seems it could be a bad solder joint on the internal diodes or other connection? I've tried to take the alternator apart, but the Phillips head screws are impossible to move, even after soaking in pb blaster and impact driver. This is the original alternator, 31 years old with 400k+ miles on it. No complaints here.
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"I get 17-18 ohms from engine to battery negative. 16-17 ohms from firewall to battery negative."
You should get zero on at least one of those. Short the two leads together. Zero? If not, try another meter. Sometimes a very low battery in the meter will cause funky readings.
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My meter is a Klein and pretty good quality for basic electronics. When I touch the leads together it shows zero ohms. I have a 10 ohm 1% resistor and it shows exactly 10 ohms on it. The resistance is very constant, and I've checked it several times over days. Higher resistance in the steel body I suppose.
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I believe every meter sold should come with a couple reference resistors for each resistance range, and clear instructions to disconnect power (battery) when making resistance readings. Good to know you checked your meter, which means you probably are aware of the difficulty probing oxidized steel and aluminum surfaces as well.
--
Art Benstein near Baltimore
"Smedley had become the Clint Eastwood of chicken crises." -Kenn Amdahl
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It's REALLY Solved this time!
So after a lot of testing, cleaning, etc and getting nowhere, I talked with a local old-school alternator shop. They said the diode block probably had bad solder joints after 31 years of heat and lots of miles. I installed a known good alternator and instantly everything is instantly fine again. I learned about about the idiot light circuit, the speedo console, where all the ground connections are located, etc, so all good here! Now onto another 400k+
Thanks to everyone who advised where to go, what to do. You all are the best! The gurus of the 240 world! Thanks so much!
Jimmy
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Hi Jimmy,
I'm happy to know those automotive electrical shops still exist in spite of Autozone, Advance, O'Reillys etal. Or maybe because of them. Kinda makes me want to find one and apply to be an intern.
Also it is great to see someone like you go for the root cause instead of the "parts cannon" on first try. The learning is more real and satisfying.
--
Art Benstein near Baltimore
A place for everything. Everything in its place. Granularity may vary. -AB
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Hi,
That 16-17-18 ohm reading is way too high for anything on the grounding side of a circuit.
It’s a ground so it’s should be a direct shot back as there are no components providing interference.
A ground is one side of a “ladder diagram” circuit with out the rungs that have the components.
I have been reading around on the thread and it hit me that this is an original alternator of 31 years!
I’m going to completely disregard the 411K mileage statement.
You say you cannot get the screws out?
Well hello?
This alternator owes you nothing as someone got the value out of it, way way too long ago.
The stators slip rings have to be bad and that explains the intermittent operation.
I know you can take the regulator out and put in new brushes.
But the slip rings cannot have a canyon walls down the middle of each ring.
If the alternator windings have never been cleaned of dirt with an air hose they may have overheated and there’s a bad spot within that open wider when warmed up.
After thinking about wires and the age factor of the whole car I’ll bet the main battery cable to the car’s body is toasted.
If you want a miracle, so the car to work again, you might have to do more work in a church parking lot with a really high spires.
Good luck with that.
Phil
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Hi Phil,
Yes we agree, the alternator has done it's job so no complaints. Surprisingly the slip rings looked good. They show some wear of course, but I do think the problem was elsewhere in the alternator. Probably windings or diode connections/board.
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