earlier this year i installed a newly re-built alternator with a potentiometer set at 14 volts. At the alternator it was showing 14 volts plus, but at the batteries could barely muster 12 volts !
needless to say, operating my car on a daily basis drains the batteries and usually need a charge on a weekly basis...
any ideas where the power loss could be or rationale?
i think this has been a chronic problem with my 8 and its just come to light this year... i used to think i had a parasitic drain but i now think this was the problem all along...
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
Possible dead batteries. Batteries can be fully charged, but when you load them up, they won't hold that charge.
Start by getting them both load tested (best if they are removed from the vehicle and tested individually).
'93 850Ci - Mineralweiß Metallic
2001 740iL - Titansilber
ALPINA B7 -Alpinweiß III
...the price of cool ain't cheap!
....also 14V is a little low, 14.6V is the correct no-load voltage.
Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i
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i had both batteries tested and they CAN and WILL hold a charge... clearly thats not my problem...
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thanks but thats not the point... only getting 12 volts to the batteries...
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looking to change up my GM... sometimes those modules control too much!! Wuffer told me he had a club guy with similar problems and after changing up the GM it went away...
However im not as convinced...
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
you sure it is charging the batteries ? (blue cable to alternator not connected, tells it to charge) Measure voltage at batteries while running (should be around 14v).
BMW 850 CSI march 1994 (EU spec), SOLD. https://www.classiccars-forsale.com/...94-bmw-850csi/
BMW 850 CSI november 1994 (EU spec)
I honestly do't think batteries are getting charged, like clubE31 suggested double check alternator install, I bet that is your problem.
i had the alternator installed professionally by a BMW shop, trust them implicitly, so does Wuffer... besides this is my 2nd Alternator in 3 years... i will try the cleaning scenario...
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no its not charging the batteries... this is my problem... not enough voltage to the Batteries! Alternator is push north of 14v... barely 12v at the batteries...
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
Thank you for the valuable information! I will endeavor to clean all connection points...
see private message...
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
battery connections can be tricky I had an issue with my truck where it seemed as tho the battery was going. It has side mount terminals and it turned out that the negative bolt was loose. It would start, but sounded like it was struggling.
On another note. My 850 had a draining battery problem. I hooked up the charger over night and the next morning pulled the batteries. the one on the passenger side was warm and only held 10 volts. the other one was holding 12v. So bad battery. replaced the bad one with an 800cca from NAPA. no more power issues.
thank you ALL for your most helpful comments, its really appreciated...
today i replaced my grounding strap (it was one of those braided straps) with a brand new 1/4" cable with metal loop ends... i wire brushed all the terminals too.
then i removed and clean the 2 hot terminals beside the fuse box in the same fashion.
Then i went into the trunk and disconnected both batteries and ALL associated cables (including ground) and cleaned them all in the same fashion.
Then reconnected the works and started the car... but first with my meter i took a reading on the battery off and read 12.60 volts. after starting my car, the voltage stayed the same... it did not jump up with juice from the alternator as it should have....
so now what?? something is preventing the 14.5 volts my Alternator discharges from getting to my batteries !!
Any ideas?
thank you in advance and Happy Thanksgiving to my Canadian brethren...
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
Fusible links?
'91 Dinan 860 Stage III (new 6L engine)
'91 Dinan 850 TT stage III (brand new engine) 21st Century Tech meets 18th Century Dinan...
'91 850i 6sp (mint) (sold)
'90 Dinan 750iL TT stage III (Guido - The Beast)
'94 850 CSi The Detroit Auto Show car (restored to factory perfect) (sold)
'96 850Ci, The George Carlin car
''73 3.0 csi, '08 535i, '03 X5 4.6is
...and a few other non BMW cars
nope checked that too... maybe GM??
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
Makes sense... is the cable under the carpet?? does it go directly to the battery or veer off or split off too?
the guy that rebuilt my Alternator installed a potentiometer on it to crank out 14 plus volts and my mechanic confirm the voltage after he installed it... thats how this issue came to light... other possibility is the main General Module... ordered a rebuilt from Wuffer, he says a similar issue in our club was resolved by the new GM...
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
Hello Starship, would you please comment in the leaking diff thread. I have the same leaking diff problem.
Before you worry about removing carpets - the first place the alternator connects to is the B+ post under the bonnet. I would suspect that this post will be at the same voltage as the batteries when the engine is running.
Giving a mechanic a potentiometer to twiddle is a recipe for disaster - and I will give you odds of 10:1 that your problem is simply the alternator - either dead or you mechanic has adjusted it to a point where it doesn't give any current out!
Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i
My BMW Repair YouTube Channel
My Current 840ci Sport Individual
My Current 650ci Sport Individual
My E31 Repair and Information Website
My E38 Repair and Information Website
My E63/E64 Repair and Information Website
Chase - Heroes to a generation
thanks for your input Timm... when i checked the voltage at the B+ post, yes its the same as the batteries with motor running however, my mechanic confirmed the 14.5 volts right at the alternator after he installed it...
thats where this witch hunt started from...
ergo the thought of the GM......
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
AFAIK, it is a single fat RED cable from the alternator to the B+ post - so should be easy to measure across. On the E32 I have seen the B+ post come a cropper, it has a bunch of cables bolted to it below the post - and corrosion can make loosen all of them - it wasn't a pretty sight.
But, I have only seen this once (Shogun will remember I'm sure), and never on the E31 - my money is still on a dead alternator.
Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i
My BMW Repair YouTube Channel
My Current 840ci Sport Individual
My Current 650ci Sport Individual
My E31 Repair and Information Website
My E38 Repair and Information Website
My E63/E64 Repair and Information Website
Chase - Heroes to a generation
UPDATE ON ALTERNATOR...
had my 8 in the shop to change a few hoses and fix heater console... same Mech as installed my Alternator few months ago... at my request i asked him to search out for broken or missing wiring, and he was successful. Had a plastic sheath at front of block with wiring inside that had broken wires inside and was determined these were a contributing factor to voltage loss at batteries. Wires repaired and voltage issue resolved.
Now 14+ volts at the Alternator, same at the B+ post under the hood and 13.8 at the batteries at IDLE...
thank you all for your valuable input !
"...i haven't taken leave of my senses Bob, I've come to them..." -- Ebenezer Scrooge
How did those wires get broken?
Wow! Congrats on your discovery.
1993 850Ci.....18 years & 165,000 miles and counting!
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