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View Full Version : Here's a road story on low voltage and 750



shogun
11-15-2006, 07:59 PM
Subject: Re: Any suggestions on these alternator issues?
Author: Mark750il
Posted on: 2006-10-05 20:01:58

Drove my 90 750iL with 132k miles on it on a 120 mile trip on Wednesday. About 112 miles into the trip, the Brake Ckt warning came up. Then the AntiLock, then the ASC, then the Check engine light. Test 09 was showing less than 9.00 v.

After about 6 more miles, the tach, speedo quit, then it died. Was able to get it to a vacant parking lot. Had a battery company come with a new battery. Got it jumped, drove it to their shop, about a mile.

(remember now, I'm 120 miles from home!)Researched the archives, and found the mention about the B1 to alternator cable, running above the exhaust manifolds. With a 2 y.o. battery, and a 2 y.o. alternator, this seems like a likely culprit. I email the garage, and ask them to check it. They say they will. I go there at 9:30 am, they say they'll check it soon. I call at 1:00pm, not checked yet.....20 minutes it'll be checked. Call 3:00 still not checked. I go there, and check the thing myself. It checks out OK. So....it points to the alternator. (still 120 miles from home, and its out in the country!!)

A tow home would be prohibitive, can't get an alternator till next week. What to do, what to do?

Buy ANOTHER battery!! Take chances that TWO batteries will get me 120 miles, w/o AC, brakes, turnsignals, radio, etc.etc.

Monitored Test09 all the way....started out about 11.7x. After 60 miles, (more than half way, and I'm still on battery #1!!) Got to mile 116, about 4 miles from home. Stuck in single lane traffic with construction on interstate interchange, Test09 goes to 8.xx, all the indicator lights come on, tach quits, speedo quits! Its about 4 seconds away from dying!!! I DON'T want to stop in the middle of all this traffic (I know I would be iritated it some idiot did that to me!!).....so I whip it around, get back on the interstate. Go 2 more miles towards the office. Test09 goes back up to 10.85. Get off, praying that the light changes REAL SOON! My MOTHER calls from AZ, and wants to chit-chat! Sorry Mom, gotta' emergency here, gotta' go! Light turns green, I crank the corner pretty hard to get outta' the intersection. Look at test09, and the OBC is really bright. Test09: 13.41 volts!!!! Drive to office, Tes09 is 12.94 ot 13.41 all the way! Leave it idling, 12.94 to 13.xx. There for 8 minutes....go home.....12.xx to 13.41 all the way home.

So....any suggestions? I think that the alt is still a bit weak, I think it should be 13.8 minimum. Did the hard turn 'un-short' a short? I think I'll pull the B+ to alt cable to see what condition it is in. Probably order another alt just to be safe. Will charge it tonight, just to get to office and back tomorrow.

Anybody else have similar effects? What was the solution??

Mark

genphreak
11-15-2006, 08:04 PM
Hahhaha... can't contribute anything here but somehting like that is what every old e31/2/4 driver has to be prepared to do sooner or later... good work Mark- a new alt/reg and I'd bet all will be good.

Barry
11-15-2006, 11:01 PM
I posted something similar at the beginning of the year with my ABS light continually coming on on my trip back from holiday.
Eventually traced it to the black Bosch 3 pin connector from the alternator to the body harness..This plug is on the intake side of the m30 motor,down at sump level.
Unplugging it I found it had got moisture in it and all the connectors were corroded-blue copper deposit in the plug.
Cleaned this out and have not had a low voltage problem since.Now I actually have a volt meter(Lighter plug -in type)In the car at all times..
Voltage is 13.6 to 14.2 volts ,depending on ancilliary usage..

shogun
11-15-2006, 11:15 PM
Barry,
thanks for the input. But don't you have a OBC installed, where you can see the actual voltage when unlocking it under test # 9?

13.6 to 14.2 Volts at the cigarette lighter plug is quite good, usually there is some loss to there or the OBC, compared to direct measurement.

euaniebabs
11-16-2006, 07:44 AM
My Old man had a similar problem in his 750. Turned out to be dodgy alternator diodes.

Symptoms as you describe and ancillary systems gradually shut down - including the power steering which was unamusing on those massive tyres.

I would check those out before heading into a wiring nightmare!

Euan

Barry
11-17-2006, 01:17 PM
Huh?????
I can do that??Sorry,did not know about this S..
Now..to find how to test with OBC...