'92 240 Charging Issue

Thats why I said to learn how to do voltage drop tests. Look it up. That ground wire on a 240 commonly goes bad from heat and oil leaks.

One day you may get to the point where you skip the dudes at the parts store all together.

I was (am? Car's put up for the winter) having issues with the charging on my 240. The alternator warning light was not on, doesn't come on when the engine is off/key on. I triple checked (Autozone Triple Check!) the wiring between the cluster and alternator, all was fine. I was having similar flaky voltage readings with the wire at the alternator.

12V+ is not always 12V+ - there might be a very low wattage supply of 12V+, not enough to actually do what it's supposed to do.

In my case:
- I tried grounding the exciter wire leading to the alternator - based on my understanding of the wiring diagram, this should light the alternator warning light (it grounds through the alternator to light the bulb), but all that did was light a few random OTHER lights on the cluster.
- I ran a jumper wire from the alternator over to 12V+ (on the battery terminal), touched it, and saw the alternator immediately start charging properly.

This all lead me to this thread: http://forums.turbobricks.com/showthread.php?t=279601
Which discusses possible faults on the instrument cluster that can cause oddness in charging since the alternator doesn't really get excited properly. I just haven't taken my cluster back out again. Before I ran into that thread I had it out to verify the bulb wasn't burned out (which will cause the same issues) - I swapped it for one I knew was good (turn signal flasher) and it still worked afterward, charging light still didn't.

ZVOLV said:

Thats why I said to learn how to do voltage drop tests. Look it up. That ground wire on a 240 commonly goes bad from heat and oil leaks.

One day you may get to the point where you skip the dudes at the parts store all together.

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I took the guy's word at face value the day he tested the alternator in the car... my fault for sure. getting ready to put the new ground wire in we'll see if that makes a difference. If not I'll be back!

On the cluster the contacts that connect to the bulb sockets for the warning lights can get a bit dirty and cause the lack of current to properly excite the alternator. Once you remove the bulbs and sockets then take the circuit board off the cluster frame. You can clean the contacts with either an eraser or a toothbrush with some of the contact cleaner like CRC QD plastic safe contact cleaner. Do this in a vented area cause that stuff stinks and isn't good to breathe. I also like Wurth contact cleaner.

Also good to carefully check where the pins connect to the board traces. that is another potential bad spot.

The 12V diving down to 1.something under the small load of the alternator exciter sure seems to indicate some sort of issue with the cluster and warning light.

With the engine off, key on, is the alternator warning light lit up?

Good point about voltage AND current. That's why I have been ranting about using a test lamp instead of a voltmeter to confirm there is enough juice in a circuit. I have measured 12v before on a dvom, bu it wasn't enough current to operate the device.

I also have been ranting about voltage drop tests to test ground and power circuits. I have had a few cars in the last couple months that were intermittent no cranks and the voltage drop test on the battery cables pointed us to the loose/damaged ground or power circuit. I had a 1990 civic with hacked battery cables and the ground from battery to chassis was completely missing. When I put one lead of meter to battery negative to ground I got a full 12v voltage drop registering on the meter!

A voltage drop test of your between your alt case and the block would have shown the bad ground wire! If it's a poor connection your meter may show something between 500mv and 1v, if it's almost completely open, you would register a voltage drop of something huge like 8-12v on your meter. Look up how to do it.

That type of testing is so helpful. Over the years I have had some pretty sneaky issues and they can be things like too much resistance in the circuit. Which gets revealed by a load test with something like a bulb. Good stuff.

I do this professionally every day. I have professional training and certificates.

Wasting your own money on misdiag is one thing, but imagine if you were my customer and I sold you a $400 alt and it didn't fix it.

I had a 1990 740 over 15 years ago where I was called in to diagnose a no charge situation. Being the rookie I was, I pulled the battery and took it to vatozone and they told me it was bad. New batt didn't fix it. Snap! Took the alternator to the parts house and then they told me that tested bad. We put an alt in it and still no charge. Phrumph! Then I finally tested the exciter wire and it was dead in the water. Fixed that and it fixed the prob.

I do voltage drop tests on charging/starting cables at least a few times a week now. Also parasitic drain tests every time I have a dead batt. The customer may be upset if they buy a battery and it goes dead overnight.

People that can use a test light, meter, a scope, and talk to the consumer without being mean to them can do very well in this growing industry. I've been an electronics tech for 30 years so I know just how much fun this electronic stuff is.

LBM240Wagon said:

...pulled the ground cable out and it looked ok, however when I bent it to straighten it out, the insulation cracked and broke apart.

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Had it happen, once while swapping in new brush kit. My last 240 alternator is an amalgamation of a known 93 altntr, old pulley, new brush kit, spare box bolts, ground wire, & B+/D+ insulator.

New ground cable and the Bosch alternator installed and it is charging again. Thanks for all the help! I was fully prepared to take the cluster out. I'll keep this thread saved in case I ever do need to.

Nice nice nice!

I was having charging issues on my 1990 245 once. All the wires/grounds, alternator, etc were fine. Turns out my alternator bracket bushings were worn out and they were causing the serpentine belt to not hold enough tension to spin the alternator properly.

*golf clap*

SO one way to diagnose that would have been to check for voltage between the engine block and alternator body with it running?

I know that's not my situation because I see it go from 12V to 13.8 when I briefly send 12V+ to the exciter terminal through a test wire.

JohnMc said:

*golf clap*

SO one way to diagnose that would have been to check for voltage between the engine block and alternator body with it running?

I know that's not my situation because I see it go from 12V to 13.8 when I briefly send 12V+ to the exciter terminal through a test wire.

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"Some alternators are mounted in rubber bushings and have a separate ground strap. If so equipped, be sure to check the voltage drop across this strap, too."

http://www.aa1car.com/library/voltage_drop_testing.htm

And its not charging again. Two trips today it was fine, now its not charging again. The hunt continues

don al?n said:

I was having charging issues on my 1990 245 once. All the wires/grounds, alternator, etc were fine. Turns out my alternator bracket bushings were worn out and they were causing the serpentine belt to not hold enough tension to spin the alternator properly.

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Thats interesting. my bushings are certainly worn out. Didn't think about that. I'll add this to the list of things to check. On a side note what is the correct belt tension? The haynes manual says .25 inch deflection if the pulleys are ~7" apart. -that all depends on the individual's strength though.

If you are still having issues with the exciter wire/charging lamp circuit, the alternator can still charge, depending. Sometimes alternators have enough residual magnetism in the field coils to self excite and start charging even without getting that exciter wire charge. I think my PV did that for decades (old alternators are better at self exciting... ahem, no double entendre intended).

Does the charging light come on with the ley on, engine off?

LBM240Wagon said:

Thats interesting. my bushings are certainly worn out. Didn't think about that. I'll add this to the list of things to check. On a side note what is the correct belt tension? The haynes manual says .25 inch deflection if the pulleys are ~7" apart. -that all depends on the individual's strength though.

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Yeah, about a 1/4 inch slack on the belt is what I remember going by. Those little accessory bushings are only a few bucks on amazon, the belt tensioner bracket also has one. I was going nuts before I found out

don al?n said:

Yeah, about a 1/4 inch slack on the belt is what I remember going by. Those little accessory bushings are only a few bucks on amazon, the belt tensioner bracket also has one. I was going nuts before I found out

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Out of curiosity, how much thread is left on your adjustment screw? I had mine almost bottomed out and could still spin the alternator pulley under the belt.