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LinkBack | Thread Tools | Display Modes |
#16
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A better test might be a resistance check between the negative battery terminal and the alternator frame. It should be zero ohms. If not clean the connections on the ground straps and check it again. Reading the voltage between the negative terminal of the battery and the engine when cranking the starter is yet another way. Voltage drop should be minimal but I might suspect a very small amount indicated like 1/4 volt perhaps. This is because of the very heavy current flowing through the ground connections and the thickness of the ground strap. The chance of a problem is increased by the age of these cars. Not that there is a problem present in the ground circuit on your car. It is just something to check just in case. |
#17
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When you are a good samaritan and boost a car it may also cost you dearly. I am not sure of the actual why of it but it is a fact. Theoretically it should not happen but it does. Not caused by reverse polarity boosting either. If I agreed to boost your car I would just tell you to keep the key off and let my alternator and battery bring your battery charge level up. Takes a little more time but we will both drive away. Usually both of you will as well if you crank the engine while boosting. There will just be a time that one or the other of you may not. |
#18
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Just an update - I replaced the voltage reg and at last check, it was reading about 12.9V with car off, and 13.6 ish with it running. I am still getting a slight drop in voltage with revving the engine (like .2v), but maybe this is normal?
I'll keep watching it and keep my battery charger in my trunk just in case... Also, it was no one's idea but mine to drive with the battery disconnected. Stupid, yes, but a lot of things you only realize were stupid in hindsight.
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1979 240D w/4 Speed Manual, Light Blue Estimated 225-275K Miles - "Lil' Chugs"
Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles |
#19
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That's good news. It sounds like the new regulator is working.
[Old-timer Rant Mode On] The old-timer way to monitor the charging system was by a zero-center ammeter. - Amps out of the battery, needle deflected to the negative side, it's discharging. - Amps into the battery, needle deflected to the positive side, it's charging. - Zero amps in or out, needle centered, battery is charged and just floating along. Ammeter installation costs more, and was all too often misinterpreted, so we got voltmeters. We might as well have an 'idiot light' or "Check Engine Now" warning. [Old-timer Rant Mode Off] |
#20
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#21
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You may want to remove and clean all grounds and battery terminal clamps in the primary battery alternator circuit. Clean them and apply a little dielectric grease of just grease and reconnect. Refreshing old grounds is not a bad ideal anyways as I have seen it improve other things. Cheap preventative maintenance as well. |
#22
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Update to this.
Last night I drove home in the dark, lights on radio blasting. Then after I parked it I went to start it again to test out this weird clutch problem I am having and battery was too low to turn starter fast enough. MORE: I charged the battery overnight. As I was driving on the freeway today, I noticed the battery light pulsing on and off at roughly 2 pulses per second fading in and out. The faster the RPM, the brighter it pulses. At idle speed, I don't see it. I checked voltage at idle and it is normal - about 13.5V ish - so can I assume the alternator is working weakly at high RPMs? Does the battery light actually warn you that the alternator (not the battery) is weak? So my problem persists. It has been a little over a week since replacing the voltage regulator, which doesn't appear to be the problem. The battery has worked for numerous starts since then, but had apparently gotten weak from the long drive with the headlights on and weak charging.
__________________
1979 240D w/4 Speed Manual, Light Blue Estimated 225-275K Miles - "Lil' Chugs"
Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles |
#23
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What's the age and tension on your belt? Something is causing the alt to not keep up with it's duty under hard load.
It could be failing contacts or pulley in the alternator. Could be that one of your other pulleys is seizing up and causing drag/slap in the belt. Do you have A/C or power steering that you notice dropping functionality at speed? If it was me (read I'm not familiar with that chasis and have another car I can drive) I'd take the belt off. See if it's worn, how the tension is. Are any of the pulleys sticking or binding? There's a place near me that can bench test alternators. Southern electronics, they do radios and speedometers and soldering, but they can bench test an alt under different loads. Good Luck! -Dave |
#24
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FIRST... which car are we dealing with?
it sounds like your alternator is worn out. as mentioned though, the belts could be slipping. (TD would have dual belts, 240D would have single belt on alt.) if you have dual belts, they need to be a MATCHED set from the same box!
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#25
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240D.
The alternator was rebuilt in July. I would need to double check, but pretty sure I remember seeing that the belt was replaced with it. A mechanic did it, as I was on a trip out town with the car when it failed.
__________________
1979 240D w/4 Speed Manual, Light Blue Estimated 225-275K Miles - "Lil' Chugs"
Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles |
#26
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Charge the battery overnight, then load test it. Voltage doesn't tell the whole story. If you don't have a load tester, you can measure voltage at the battery while cranking: shouldn't drop below 10 or 11.
Cables need to be clean and tight at the battery, body ground, and starter. A weak point in the wiring is the connector which plugs into the vr at the alt. Check that the three connectors in the plug aren't loose. Like has been said, the vr has to have a clean ground at the alt. If all of these things are ok, and the belt is tight and not worn out, the issue might be a diode or wire in the alt itself. I bet the battery is weak. |
#27
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I brought the battery in to be tested at the place I bought it.
They said it would be 45 min to test it, but after about 10 they said it was fine.
__________________
1979 240D w/4 Speed Manual, Light Blue Estimated 225-275K Miles - "Lil' Chugs"
Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles |
#28
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Checking for adaquate belt tension is easy. Just reach in with the engine off and see if you can turn the fins of the cooling fan on most alternators. If you can at all the belt or belts are too loose or worn out.
Usually when a belt wears heavily it may contact the bottom of a pulley groove. When this happens it cannot gain side traction. This said usually loose belts like to squeel under heavy electrical load just after you start up and pull away. Unfortunatly a lot of rebuilt alternators are also suspect. Do you still have any warranty left on yours? I would give it one more chance before calling it probably intermittent. Cleaning and treating all the relavent connections first. |
#29
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i've recently had charging problems with both my 240Ds and after having alternators pulled, tested OK, batteries pulled, charged, tested OK, i found each to be a wiring problem. on both cars, it would sometimes charge fine, sometimes battery light would flicker, sometimes be off but then not enough juice to start,etc..
so once you have your alternator and battery tested and they are OK- maybe look into the wiring-- on one car it was the positive cable going from the battery to the starter. it looked fine from the outside, i repeatedly cleaned the battery terminal,etc. but once i just took it completely out it was obvious that the wires INSIDE the battery terminal were way nasty. the were corroded and probably making partial intermittent contact.. replace that cable and everything works great ever since. on the 240D, it was a longer process of testing every wire,and i thought at first changing the regulator had solved the issue, but finally found it to be the wireharness on the back of the alternator- same thing, it LOOKED ok on first look, and made a tight connection, and even tested OK when probing in there with a volt meter. i finally just cut it out and seeing out of the vehicle - the inside of the connectors were very corroded and worn- and again making intermittent contact, sometimes partial contact where i'd get some charge, but not full, etc.. i replace the harness with new standard wire quick connectors and it works great now, everything charges as it should. my thread on it has pics of the connectors i used. if you already have connectors as i did, it was a quick, easy, inexpensive piece of the puzzle to rule out, and for me it happened to be the culprit.
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1981 240D ... 265k 1977 240D ... 265k 1977 240D ... 250k |
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