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Old 01-04-2018, 04:52 PM   #26
ZVOLV
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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.
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Old 01-04-2018, 05:02 PM   #27
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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.
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Old 01-04-2018, 05:18 PM   #28
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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.
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Old 01-04-2018, 08:24 PM   #29
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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.
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Old 01-05-2018, 03:50 AM   #30
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...pulled the ground cable out and it looked ok, however when I bent it to straighten it out, the insulation cracked and broke apart.
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.
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Old 01-05-2018, 10:16 AM   #31
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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.
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Old 01-05-2018, 10:36 AM   #32
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Nice nice nice!
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Old 01-05-2018, 11:26 AM   #33
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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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Old 01-05-2018, 11:28 AM   #34
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*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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Old 01-05-2018, 12:24 PM   #35
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*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.
"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

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Old 01-05-2018, 04:28 PM   #36
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And its not charging again. Two trips today it was fine, now its not charging again. The hunt continues
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Old 01-05-2018, 04:30 PM   #37
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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.
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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Old 01-05-2018, 04:34 PM   #38
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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?
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Old 01-05-2018, 04:53 PM   #39
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Originally Posted by LBM240Wagon View Post
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.
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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Old 01-05-2018, 05:05 PM   #40
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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
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.
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Old 01-05-2018, 05:09 PM   #41
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Try manually slapping 12v to the exciter terminal via a jumper wire from battery positive or alt positive. It only needs one slap per drive.

The exciter wire commonly goes bad underneath the engine. I ran a new wire.
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Old 01-05-2018, 06:20 PM   #42
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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.
I don't remember, honestly. When I would adjust the alternator, I would just loosen the adjustment screw, push down on the alternator to the desired tension and re-tighten the screw. Don't know if this is the official way but it worked for me.
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Old 01-05-2018, 06:26 PM   #43
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It depends on how bad your bushings are!
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Old 01-05-2018, 08:23 PM   #44
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It depends on how bad your bushings are!
The alternator rocks and the tensioner screw runs out of threads. I bought a few new bushings from IPD this afternoon. Going to change them regardless. I was smelling something that I thought was belts, but I chalked it up to the new electric fan going thru its first couple heat cycles. With the bushing, I bet it was belt.

I'm down until tomorrow. The 16 year old tensioner screw snapped on me. Looks like an M6x100?
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Old 01-05-2018, 09:55 PM   #45
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I think the adjuster screw is M6 x 70mm. If you have a 100mm bolt and need to shorten it. Screw on a couple M6 nuts past the new length. Then cut the bolt to length. Next use a file and smooth the end of the bolt so it tapers to a rounded flat end. Now unscrew the M6 nuts and it will form a good starter thread on the end of the bolt.
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Old 01-06-2018, 05:35 PM   #46
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Originally Posted by LBM240Wagon View Post
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.
Another possible problem of worn bushings is pulley alignment (additional stress on altenator bearings)
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Old 01-06-2018, 09:02 PM   #47
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After toying with it again today I discovered that that belt I had on there was impossible to tension properly (thus why the old adjuster screw broke). I could not back the alternator away from the block enough, it had hit the max adjustment in the tensioner bracket. I double checked the belt size, and it was a 36.5" belt that showed correct per Advance's and Autozone's website. I went to Autozone this time and got a 36" and 35.5" belt, got home and put the 36" on. it was too short.... Knowing the 35.5" would not work, I went back and swapped it for their flavor of the correct 36.5" belt and put it on. Perfect, and somehow smaller than the 36.5" belt I got from Advance 3 weeks ago. Tightened it all down and it is charging again. I have an old marine volt meter kicking around in the garage, I'm going to wire that up and watch it for the next few days until my new bushings come in.

Not sure what was up with the first belt I replaced 3 weeks ago, but that very well could have been the genesis of all my troubles this week.
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Old 01-06-2018, 09:36 PM   #48
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Glad you got it sorted. Always good to have a volt gauge. Get a 52mm size one and you can buy the single gauge stuff for the dash on ebay to have one in the dash. I like to use the VDO cockpit and vision gauges.
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Old 01-07-2018, 10:01 AM   #49
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Glad you got it sorted. Always good to have a volt gauge. Get a 52mm size one and you can buy the single gauge stuff for the dash on ebay to have one in the dash. I like to use the VDO cockpit and vision gauges.

Yes, been looking for a period correct one as mentioned!
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Old 01-07-2018, 11:28 AM   #50
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