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Author
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Topic: Battery Voltage drops...
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outlawd94cobra
SR.CITIZEN
Member # 265
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posted
 
 
A few days ago i left my headlights on for about 2 hours and it completely drained my old battery. I had to get it jumped just so it would start, i thought everything would be fine once i got the car running and the alternator pumping, but when i would turn the heater/AC on at a stop the voltage would drop and the car would sound like it was going to die. Took the Cobra to Sears had them check it twice and both times the results were bad battery, good alternator. Picked up a new DieHard GOLD and everything went away for 2 days until last night, my brothers car needed a jump and soon after the voltage problem came back slightly. Not as bad as before though. This is seriously urking me. All i can think of is the following....
a) dirty or clogged air filter
b) using 89 octane (for the past week and a half instead of 91$$$)going back to 91 today
c)ignition coil?
d)idle on the TB needs to be adjusted a tad bit higher
never had any problems before the battery died, so its really annoying. Everything (plugs, wires, cap, rotor, belt,) is brand new and within a range of 4k. What else could it be?
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CRYSTAL WHITE 1994 COBRA; TOTALED
RIO RED 1994 COBRA INDY PACE CAR; SOLD(now in VACAVILLE)
(#18 of 1000)
BLACK 2002 GT Vert' AUTO; GONE!
Posts: 635 | From: Stockton, CA | Registered: May 2001
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Stimson
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Member # 51
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posted
If both ends of the battery AND alternator wires have solid connections, I'd suspect the alternator before any of the other things you listed.... even though 3G's are known to be much more trouble free compared to the 2G's.
Posts: 2373 | Registered: Jun 2000
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outlawd94cobra
SR.CITIZEN
Member # 265
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posted
I too first suspected the alternator, but both tests came out good. Also, with the heater/AC on and the car was moving,the voltage was fine,and the alternator was charging. Its just if im coming to a stop and i have the accessories on, it will go from a 800RPM idle to like 600 and then come right back up. I dont know, i might have an alternator thats about to go out. But yeah, if the heater/AC is off, the car is just fine.
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CRYSTAL WHITE 1994 COBRA; TOTALED
RIO RED 1994 COBRA INDY PACE CAR; SOLD(now in VACAVILLE)
(#18 of 1000)
BLACK 2002 GT Vert' AUTO; GONE!
Posts: 635 | From: Stockton, CA | Registered: May 2001
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Stimson
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Member # 51
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posted
Any codes from the EEC?
Posts: 2373 | Registered: Jun 2000
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FasterDamnit
Bad Attitude
Member # 442
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posted
Very simple system for electrical power- battery runs the starter motor, alternator generates 14VDC w/ engine running. If voltage is dropping at idle under load, then the alt is not supplying enough power. To test it at home, use a voltmeter (borrow if necessary, or spend $12 at Radio Shack) and put the leads on the battery posts. With the car idliong and no accesories on, should be 14.5 volts (give or take a couple of tenths.) With ALL accessories on and the headlights on high beams, should not drop below 13 (might go as low as 12.5 w/ 75 amp alt.) If it drops to 12.0 or lower, the alt is bad. A 3G alt will hold better than 13V w/ all acc. running.
JL
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'92 LX T5
Looked stock, went 11's 11.90 at 115mph.
'65 Mustang 347
www.fordmuscle.com
Livin' in the Carolina Pines
Posts: 2971 | From: NorCal | Registered: Sep 2001
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outlawd94cobra
SR.CITIZEN
Member # 265
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posted
Thats one of the same tests they ran for me when i picked up the DieHard. On the printout, the alternator was fine , and at idle with the car under load (ie:highbeams, AC/Heater, stereo, rear defrost on) it printed out as a good alternator. The only negative response i got back was when they did the two tests with the bad battery and that reading dropped to about 9.9
Put in the new battery, tested it twice, once at idle w/ everything off, and the second time under load and everything was fine, alternator and battery. So i still dont know what it could be.
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CRYSTAL WHITE 1994 COBRA; TOTALED
RIO RED 1994 COBRA INDY PACE CAR; SOLD(now in VACAVILLE)
(#18 of 1000)
BLACK 2002 GT Vert' AUTO; GONE!
Posts: 635 | From: Stockton, CA | Registered: May 2001
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Tyrant89
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Member # 1033
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posted
I have a similar prob w/ my 89. With all accesories (mainly fan & headlights) the car won't charge. I have yet to use voltometer, but my stocker seems pretty accurate.
My next step is to check wiring. I have been told that a bad ground can cause this, and to remove individual fuses till the volts jump back up.
I have a powermaster 140 AMP alternator. But it does have a U/D pulley on it. That's coming off next.
Posts: 260 | From: Salinas, holmes! | Registered: Mar 2002
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outlawd94cobra
SR.CITIZEN
Member # 265
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posted
So far as of this past Sunday morning, had the battery and alternator tested again twice. Under load, car stayed at 14v+. Alternator turned out to be fine. That was after disconnecting the battery and wiping down some AC/Heater/Refrigerant fluid from the engine bay and battery posts, fixing the AC line hose that had sprung a leak from getting bent when the plugs were changed, re-securing all the battery cables extremely tight, adjusting the idle, and filling up with some 91 octane. Hell, i thought that was'nt even gonna work, but it did. Going on 48 hours almost w/ NO problems under load.
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CRYSTAL WHITE 1994 COBRA; TOTALED
RIO RED 1994 COBRA INDY PACE CAR; SOLD(now in VACAVILLE)
(#18 of 1000)
BLACK 2002 GT Vert' AUTO; GONE!
Posts: 635 | From: Stockton, CA | Registered: May 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
Having your car jumped & jumping cars can damage the alternator. Jumping a car with your alternator turning uses the alternator to turn the other cars starter....VERY hard on the alternator first off, but second as soon as the other motor fires up, that alternator starts charging the bat & the excess amperage in the cables (even if just for a split second) can send a power surge back to the alt & pop a diod. Same with the alt on the car being jumped.
Safest way to jump a car is to hook the batteries together without the other motor running. Just let the one battery charge the other for a few minutes, then try to start the motor. Or just swap batteries, keep the motor reved a little & swap the dead bat back in.
Sounds to me like you blew one of the diods on the Alt. I've done it.....a few times.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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outlawd94cobra
SR.CITIZEN
Member # 265
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posted
No pullies.....but yeah, since Sunday morning, the cars been running fine, been using the heater on high and everything with no worries and no problems.
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CRYSTAL WHITE 1994 COBRA; TOTALED
RIO RED 1994 COBRA INDY PACE CAR; SOLD(now in VACAVILLE)
(#18 of 1000)
BLACK 2002 GT Vert' AUTO; GONE!
Posts: 635 | From: Stockton, CA | Registered: May 2001
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