Date registered: Jan 2015
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Help Please for charging problem
I have a 1984 300CD with a Bosch AL117X alternator on it and a good battery barely a year old, and the system is having intermittent charging problems which might have been the cause of the earlier battery's failure. I've installed a voltmeter to track operating voltage and sometimes the battery is just barely getting a charge of 13.6 or 13.7 V but most of the time the system gets into a discharging state as low as 11.7 V. This is with minimal use of accessories and lights, although the a/c fan is jumpered permanently on it only accounts for about 0.2 or 0.3 V voltage drop. I took the alternator to two parts stores for dynamic testing and both passed it as functional. Cleaning the electrical contacts on both sides of the plug seemed to help a little bit for a while but it could have been coincidence and it didn't last. Even though it passed both dynamic tests I thought it could still be the voltage regulator sometimes making better brush contacts or something, so I replaced the voltage regulator and it brought the system voltage up to about 13.7 V for about ten minutes at idle but later I took it on the road and it dropped down like before. It does seem that the system most often works better when the engine's cold rather than warm, but that is not always the case. If at idle it's for example at 11.8 V then gunning the engine to 2500 rpm or so might bring it up to 12.1 V or so, not the 14.5 or so volts it should be.
Next I'm going to establish a temporary new ground connection between the engine and body in case that's the problem. If that doesn't change anything I plan to pull all the fuses to see if there's some kind of huge parasitic voltage drain I don't know about, though I haven't noticed any smoke or unusual heat anywhere. If that doesn't help then the only thing left I can think of is that it's got to be a wiring harness problem and a real pain to track down. Do any of you have any other ideas about what could be wrong or what I should check?