 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / BMW Cars / April 2004Can an intermittent grounding problem kill a battery
I have an '88 325i (e30) that has been diagnosed to have a electrical problem by an experienced BMW mechanic. The the principal symptoms have been a rising temperature gauge that will go higher proportionately with the number of things that are using electricity. For example, it will move to the beat of my flashers and will jump higher depending on the speed of my AC/Heating fan. The mechanic tighened the bolts on the oil pan and that helped for a while but the symptoms came back after a couple of months. I'm guessing that this helped, for a while, to fully close the circuit between the engine and the battery (negative) ground terminal. I can live with this problem (more or less), but recently a 6 month-old battery died on me and could not hold a charge. It was replaced under warranty and I was told the battery was defective. I'm still concerned that this grounding problem may be killing my battery and I might not be so lucky with a warranty the next time. The Alternator tests fine, by the way. Any ideas to fix perminently? Also, can this problem damage a battery? Fell free to e-mail me your ideas. Thanks, --Matt Yes, it can. Your battery is never properly charged due to current/voltage loss. A. > I have an '88 325i (e30) that has been diagnosed to have a electrical > problem by an experienced BMW mechanic. The the principal symptoms [quoted text clipped - 22 lines] > > --Matt > The mechanic tighened the bolts on the oil pan and that helped for a > while but the symptoms came back after a couple of months. I'm > guessing that this helped, for a while, to fully close the circuit > between the engine and the battery (negative) ground terminal. Novel.  Signature*This message has been ROT-13 encrypted twice for extra security * Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn If the battery was under-charged, you should have noticed the car being hard to start long before the battery failed completely. A more common cause of premature death for batteries is overcharging. If you have a volt meter, measure the voltage at the battery terminals with the engine running. Rev the engine up to a few thousand RPM. Different car makers have different specs for voltage, but 14.0 V +/- 0.5 V and 14.5 V +/- 0.5 V are very common specs. If the voltage exceeds 15 V as you rev the engine, you have a problem with the charging circuit, most likely a broken voltage regulator. This sort of failure will kill a battery quickly. It will also have the symptoms you described by inference, that the system voltage changes with electrical load. It is normal for the system voltage to drop a bit below spec at idle, but as you rev the engine it should quickly stabilize and stay very constant no matter how high you rev the engine. If the voltage ever exceeds 18V, stop the test immediately to avoid damage to the car electronics. If you do have a voltage regulator problem, get it fixed quickly. Excess voltage not only damages the battery, it can take down all sorts of electronic gadgets (ECU etc.) with it. > I have an '88 325i (e30) that has been diagnosed to have a electrical > problem by an experienced BMW mechanic. The the principal symptoms [quoted text clipped - 22 lines] > > --Matt > If the battery was under-charged, you should have noticed the car being > hard to start long before the battery failed completely. That's not my experience though. My BMWs (E30 and E39) were starting just fine until they suddenly completely stopped cranking one morning. The batteries were quite dead (< 12 volts). One way to test for a weak battery may be to idle the car and then turn on every electrical device and watch to see if your headlights dim and then brighten as you rev the engine. A more common > cause of premature death for batteries is overcharging. If you have a > volt meter, measure the voltage at the battery terminals with the engine [quoted text clipped - 5 lines] > quickly. It will also have the symptoms you described by inference, that > the system voltage changes with electrical load. Yes, overcharging can easily kill a battery but shouldn't that level of damage show obvious signs such as acid spillage from gassing? Could the poor re-charging of the battery not also be caused by a loose terminal or a bad cable? > It is normal for the system voltage to drop a bit below spec at idle, > but as you rev the engine it should quickly stabilize and stay very > constant no matter how high you rev the engine. If the voltage ever > exceeds 18V, stop the test immediately to avoid damage to the car > electronics. The E30 charging system should operate between 13.5 to 14.2 volts. > If you do have a voltage regulator problem, get it fixed quickly. Excess > voltage not only damages the battery, it can take down all sorts of > electronic gadgets (ECU etc.) with it. I agree. Michael > > I have an '88 325i (e30) that has been diagnosed to have a electrical > > problem by an experienced BMW mechanic. The the principal symptoms [quoted text clipped - 22 lines] > > > > --Matt > If you have a volt meter, measure the voltage at the battery terminals > with the engine running. Rev the engine up to a few thousand RPM. > Different car makers have different specs for voltage, but 14.0 V +/- > 0.5 V and 14.5 V +/- 0.5 V are very common specs. If the voltage exceeds > 15 V as you rev the engine, you have a problem with the charging > circuit, most likely a broken voltage regulator. Most recent cars tend to have the lower figure to prevent overcharging low maintenance batteries, and as a result, never *quite* fully charge any. In practice, this shouldn't matter. As regards faulty regulators, they usually fail short circuit, so as you say can produce pretty high voltages. A lower than normal reading is commonly a failed diode - but of course don't neglect to check properly all the connections first. Signature*I'm not as think as you drunk I am. Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn Thanks to all for the quick diagnostics. I ran some tests with a multimeter across the battery terminals. Here are my figures for a new (1 week old) battery: Car Idleling: 13.6 - 13.7 V Car Idleling with radio, lights, and AC Fan Running: 12.6 V Car with throttle open(@ 3000 RPM)and with radio, lights, and AC Fan Running: 12.6V Are these readings "lower than normal" for an 1988 e30? --Matt > > If you have a volt meter, measure the voltage at the battery terminals > > with the engine running. Rev the engine up to a few thousand RPM. [quoted text clipped - 11 lines] > commonly a failed diode - but of course don't neglect to check properly > all the connections first. > Car Idleling: 13.6 - 13.7 V > Car Idleling with radio, lights, and AC Fan Running: 12.6 V > Car with throttle open(@ 3000 RPM)and with radio, lights, and AC Fan > Running: 12.6V > Are these readings "lower than normal" for an 1988 e30? Yes. 12.6v with the engine at speed won't charge the battery. But you need to know the sate of charge of the battery first - I suppose it's possible that if the battery is flat it might be this low with load. Best to charge the battery first - then check again. Signature*Therapy is expensive, poppin' bubble wrap is cheap! You choose. Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn > > Car Idleling: 13.6 - 13.7 V > > Car Idleling with radio, lights, and AC Fan Running: 12.6 V [quoted text clipped - 8 lines] > > Best to charge the battery first - then check again. You can test the battery's state of charge with an open-circuit load test. Leave the engine OFF. Turn headlights ON for 1 minute. Disconnect the battery ground cable. Test battery terminals with a DIGITAL voltmeter (don't use analog meter). The following voltages indicate state of charge: 12.6V or more = fully charged 12.4V = 75% charge 12.2V = 50% 12.0V = 25% less than or equal to 11.7V = fully discharged BTW, did they test the voltage regulator when they tested the alternator? Michael > Test battery terminals with a DIGITAL voltmeter (don't use analog meter). Why? Signature*El nino made me do it Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn > > Test battery terminals with a DIGITAL voltmeter (don't use analog meter). > > Why? perhaps he thinks they're more precise than the analog ones... or have higher input impendance, hence present lower "load" on the battery. either way - wrong. > > Test battery terminals with a DIGITAL voltmeter (don't use analog meter). > > Why? That's a fair question. I do it just as a general precaution when working around the car. Although battery testing is pretty innocuous you can easily take that same meter and test circuits with it afterwards if you're not mindful. Analog meters are not suitable for testing sensitive car circuits as some analog meters can draw enough current to cause damage. Michael > > > Test battery terminals with a DIGITAL voltmeter (don't use analog > > > meter). > > Why? > That's a fair question. > I do it just as a general precaution when working around the car. > Although battery testing is pretty innocuous you can easily take that > same meter and test circuits with it afterwards if you're not mindful. > Analog meters are not suitable for testing sensitive car circuits as > some analog meters can draw enough current to cause damage. If you're checking electronic circuits - perhaps sensors in the fuel injection system, then a high impedance meter is a good idea. Its actually not when checking the things most will like lighting circuits etc as the tiny current drawn won't show up a high resistance - a common cause of problems in an older car. Most reasonable analogue meters will have a resistance of 10,000 ohms per volt on DC. I'd be most surprised if using one of these would damage anything on a car, although it might well give an inaccurate reading, compared to a high impedance DVM. Signature*I don't suffer from insanity -- I'm a carrier Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn > > > Test battery terminals with a DIGITAL voltmeter (don't use analog meter). > > [quoted text clipped - 9 lines] > > Michael I'd say no need to worry Michael, current draw is not an issue here. Analog meters (I dare say for the last 15 years) are with electronic circuitry in the front end - it is not the voltage you read that deviates your needle but the OP amp which does some other stuff too. Whenever there's some sort of "tuning" required analog scale is much better. Alex > Analog meters (I dare say for the last 15 years) are with > electronic circuitry in the front end - it is not the voltage > you read that deviates your needle but the OP amp which > does some other stuff too. Whenever there's some sort of > "tuning" required analog scale is much better. If purchasing a good DVM, get one with an 'analogue' or strip readout as well as the digits - it helps to give an indication of a varying voltage. etc. Signature*Some people are alive only because it's illegal to kill them * Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn > > Analog meters (I dare say for the last 15 years) are with > > electronic circuitry in the front end - it is not the voltage [quoted text clipped - 5 lines] > well as the digits - it helps to give an indication of a varying voltage. > etc. I have Fluke and Major. Both analog/digital. Yet, on IFR Communication Monitor apart from digital frequency readout all the rest is analog (power, sensitivity etc). IMHO, it's much easier to tune transmitter output to maximum smoke :) Alex Can't say how well they checked the Alternator but I did some further testing of the electrical systems at night. With the headlights on and running at about 2500 RPM, there is a noticeable dimming when the A/C fan is put to max. I've also noted that there is a 0.25V difference between the engine and the ground (on the front suspension strut) when the car is running. I think that the battery, brand new as it is, is probably fine right now. --Matt > > > Car Idleling: 13.6 - 13.7 V > > > Car Idleling with radio, lights, and AC Fan Running: 12.6 V [quoted text clipped - 25 lines] > > Michael How old is the alternator? Worn brushes in the alternator is a common cause of insufficient output. If you have the original alternator still, it would be quite normal if it needed new brushes. On many cars of that era the brushes were easy to replace without even taking the alternator out from the car. > Can't say how well they checked the Alternator but I did some further > testing of the electrical systems at night. With the headlights on [quoted text clipped - 39 lines] > > > > Michael |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.