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Capt. Obvious! 01-31-2013 12:43 AM

Pulling my hair out! Battery? alternator? Grounds?
When I turn my headlights on at idle, it bogs the engine down and kills it. I has been doing this for a couple weeks now.

First it did it a couple times till, it killed the battery enough that the car wouldn't start. Charged the battery up, drove it around a little bit, started it a couple times let it idle for a while, had the battery tested and they said it was fine, readings were all within spec for that battery. Drove it for about an hour and a half. Drove just fine, although the radio kept going off. I noticed that when I get to a stop light, sometimes it would idle really low and rough. Got home drove it a couple times on short trips and then the lights started killing it again. At this point I decided it must be the alternator. Charged the battery, changed the alternator, tested the voltage with the car running (14.?v) drives fine (still rough at idle occasionally), for about two days. Dies with headlights again last night. Battery is too weak to start the car, so I checked the voltage, it was low (11.9v) So I checked the voltage at various points to see if I had a bad ground, nothing really stood out.

I tested the following points with the engine off (11.9v wont start it) and all the accesories off.

Accross the + and - terminal of the Batt (11.9v)
+ terminal to cylinder head (11.9v)
+ terminal to various chassis points (11.9v)
+ terminal to alternator housing (11.9v)

I'm considering getting a new battery today, maybe the battery tester was wrong. Any other advice before I go blow $100 on a battery I may not need, two days before I leave for vacation???

sleepyboy 01-31-2013 02:23 AM

Moved to Technical Chat

sleepyboy 01-31-2013 02:25 AM

I'd try changing the battery cables that go from the alternator to the starter and then to the battery. I'd also check the lights and any wiring associated with them for shorts.

Capt. Obvious! 01-31-2013 04:07 AM

I've already tested the headlight harness, it seemed ok. I redid them just to be safe, they are now relayed directly from the battery. This didn't help though, it still acts just the same. I will continue by testing the cables at the starter and alternator when I get home.

whynotthinkwhynot 01-31-2013 05:02 AM

Check ground connection from the battery to the engine block, from battery to chassis, and from chassis to cylinder head.

I think there is a ground that goes from the battery to the fuse box- but maybe not. That one might be the problem if it is. It seems to me that somehow one of the other relays- ignition or fuel is losing voltage and dropping out when you turn on your headlights. That doesn't jive with the battery loss of voltage though.

Have you used test mode to verify that your alternator voltage is remaining steady while driving? You might have one of those loose alternator plug-in connectors, or lost a wire in that harness. That would cause a good alternator to not put out.

Capt. Obvious! 01-31-2013 06:27 AM

How do I use test mode to do this check? What is test mode? I'll recheck the connections of those grounds and the alternator when I get home, I was kind of suspecting the grounds to be the culprit.

gonefhsn 01-31-2013 07:05 AM

Push and hold the trip odometer reset button IIRC for 30 seconds and while holding turn the ignition switch on.

Capt. Obvious! 01-31-2013 11:04 AM

Ok, I checked all the grounds and cleaned them up. That is not the problem. I found that I am getting no voltage from the alternator. I checked the voltage and it was only 11.7v at the alternator(same as the battery). I'm starting to think that maybe the voltage regulator is not getting the signal to come on. Any idea how I could check this???

FocusedSlayer 01-31-2013 11:12 AM

When I changed out my alternator , 1 of the plugs wasn't snapped on all the way like it was suppose to be causing mine not to fully charge like its suppose too. I've always been told to never put and alternator on without a fully charged battery as it could cause damage to the new alternator and battery.
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Capt. Obvious! 01-31-2013 11:46 AM

When I put the alternator in the battery was charged, that was Saturday though. It has died down since then. I checked the connections they all seem to be tight. I think it is the signal to the voltage regulator not being present. I would test it, but I don't know how.

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