Weirdness: Does this sound like a voltage regulator or the ETA? - Mercedes-Benz Forum
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post #1 of 28 (permalink) Old 07-05-2015, 07:55 AM Thread Starter
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Weirdness: Does this sound like a voltage regulator or the ETA? (RESOLVED)

Hi all-

So, after many months of trouble-free motoring in our '95 E320, catastrophe hit after fueling up for a long weekend out of town (so I guess I'm glad it happened before we got on the road!).

Car was running absolutely fine for morning errands. I stopped to top off the fuel, and when I restarted the car I was greeted with ABS and SRS lights, along with a low/surging idle and erratic A/C blower speed. The A/C compressor was also MIA. I immediately tried shutting off the car and restarting. My first restart attempt was met with a rapid solenoid click (ala a dead battery), but the car restarted fine on second attempt. The SRS and ABS lights came on and then off as normal, but illuminated again within a few seconds.

Since I was close to home, I elected to drive it back to the garage. On the way home, I noted that car was *not* in limp mode, and was accelerating normally. The cruise control also worked normally during a brief test.

As we were overdue for getting on the road, I shut the car off, and we loaded up in our Silverado crew cab and headed out of town. So at this point I've had three days to stress out about what it *might* be, but no chance to run further diagnostics. As the wagon is my wife's daily, it's in my best interest to get the old girl up and running again ASAP.

So do these symptoms sound more indicative of the voltage regulator, or the ETA? I've thus far taken a "if it's not broke don't fix it" approach with the ETA, and I'm honestly not certain that it hasn't already been addressed (the main harness certainly has). Any additional input would be much appreciated.

Cheers-

jj

Last edited by DeluxeOKC; 07-08-2015 at 08:03 PM.
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post #2 of 28 (permalink) Old 07-05-2015, 08:24 AM
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voltage regulator is trivial to test, just hook a volt meter up to the battery with the car running, it should be around 14V.

the OVP relay randomly and spontaneously conked out on my wife's 94 E320 wagon, causing a total no-start (crank-crank-chuff-crank-crank-putt, but it wouldn't start)


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post #3 of 28 (permalink) Old 07-05-2015, 09:31 AM
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Sounds like my old210 when the alternator was playing up.
The alternator was not charging on tickover,hence it
Would go flat in traffic if you had lots of electrical items turned on.
New brushes cured it.
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post #4 of 28 (permalink) Old 07-05-2015, 08:14 PM Thread Starter
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Update: After I returned home this evening (the car having sat untouched since Friday morning), I tried to start the car and got only a solenoid click. I elected to remove the battery (installed 10/12) and run it over to my FLAPS for a quick charge-and-test. They called a couple hours later and reported that the battery charged fully and tested 100%. So, I retrieved and reinstalled the battery. With the ignition off, I saw 12.8V at the positive terminal. I fired the car up, and with the A/C and headlights on I was getting 11.52 at the positive terminal. So, there's clearly a charging issue, and I figured I'd start with the voltage regulator.

Got the car up on ramps, crawled underneath with a few tools, and had the regulator extracted in less than 10 minutes. Thing is, it's got some wear but it doesn't look *that* bad (image attached). Likewise the alternator poles have some wear but no grooving to speak of (the car currently has 134k miles). But I guess for $40, it's worth swapping the regulator out to see if that fixes the problem?
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post #5 of 28 (permalink) Old 07-05-2015, 09:00 PM
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stop the engine, turn on the car without starting it and check the voltage at terminal 64 (the small screw on the right side of the battery/generator terminal strip thats immediately in front of the battery on the back of the false firewall and the back side of the strut tower)... that should read 9-10 volts or something, thats the D+ "bootstrap" circuit from the ignition switch. the generator light on the dashboard should be on. now start the car, the generator light should go out completely and not be glowing dimly and terminal 64 should be full charging voltage relative to ground.

with the engine running, check the voltage between battery - and body ground (the ground screws on the suspension hump), that should be 0V or close as what don't matter (certainly well less than 0.1V). I forget how accessible the alternator is, but if you can check the voltage from the alternator ground to battery -, that also should be 0V.

if you see like 1V or more difference on any of these grounds, then the alternator is probably working, but the pookah isn't getting to the battery.
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post #6 of 28 (permalink) Old 07-06-2015, 11:31 AM Thread Starter
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Another update... Swapped out the voltage regulator this morning, and (of course) it didn't solve the problem. However, when I went to start and test the car, I noted that none of the idiot lights on the left side of the cluster are illuminating at all. I've been poring over related forum posts all morning, but still have no clear picture of where to go next.

• I've seen some information that points straight to a faulty diode in the alternator itself, and other info that suggest the alts rarely fail at all. I did note that the existing alt is a reman Bosch unit.

• I've also read that the battery/charge bulb may be burned out, preventing a charge

• I've seen that problem might be ground-related, but I've had no previous grounding issues, nor do any of the visible ground connections appear corroded.

I really don't want to have to just keep throwing parts at this thing. Any advice is much appreciated!

jj
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post #7 of 28 (permalink) Old 07-06-2015, 11:36 AM
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did you try those voltage tests I carefully detailed? that will tell you right off if you have a grounding problem.


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post #8 of 28 (permalink) Old 07-06-2015, 11:50 AM Thread Starter
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Quote:
Originally Posted by volvo745 View Post
did you try those voltage tests I carefully detailed? that will tell you right off if you have a grounding problem.
I somehow managed to skip right over those. Thanks very much for detailing the proper voltages; that'll be my next series of tests this afternoon. I'll detail my findings afterward.

Many thanks!
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post #9 of 28 (permalink) Old 07-06-2015, 12:03 PM
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I'm not 100% sure what the right voltage on circuit 64 (D+) is with the engine off, but its likely to be somewhat less than battery voltage. probably anything more than about 6V is fine, the important thing is that there IS some voltage there.


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post #10 of 28 (permalink) Old 07-06-2015, 01:01 PM Thread Starter
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Okay, I ran volvo745’s procedures as outlined in his previous posts.

First off, I *think* I figured out where T64 is, which I’ve circled in red in one of the attached pics. Assuming that’s the case, with the ignition on (but the car not running), I was getting something like 11.74V at T64, which was the same voltage I was getting at battery+. Because I currently have no left-side warning light functionality, I couldn’t reference the battery/gen light at all.

With the engine running, I was getting jumpy voltage readings across several of the grounds, measuring as high as 9.4V with the VOM reading between bat- and ground+ (also pictured below). I assume this is not good.
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