Question about 2004 Ford F150

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After i changed my alternator, my check charging system light and battery light comes on, also, my idle is very low now. when I pull up to a stop, truck stalls, I checked my alternator output and its at 14.5 volts and the battery is checking out at 12.2 volts.

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Was the light on before you changed the alternator? Check a couple of things: Check the connections if one is loose you may be running mainly off the battery but still show it's charging. Have you checked the battery under a load? Try checking the battery voltage with the car off and turning on the headlights. What does it read? 12.2 sounds like you may have a dead cell or if you have a bad connection you may be draining it. Sometimes a battery may show correct voltage but when load is applied it drops like a rock. if this happens replace the battery. Did the idle change when you changed the alternator or has it always been low?

Posted on Dec 29, 2010


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Hi all...I was stuck in a horrible traffic jam 4 2 which 1 1/2 hrs were less than 5 mph. My truck is a 2003 Ford Escape. My radio went out then the lights started 2 dim and a brake light came...

I suppose its possible the alternator stopped charging the battery enough at the low engine speed but then worked on the way home.
The alternator will charge 12 - 13 volts at idle, but you could have enough accessories and the cooling fan running to use more voltage or amps than it is producing. Stopping at a traffic light for a couple of minutes does not hurt anything since the battery is usually fully charged. But idling for an hour or more with everything on could run the battery down.
You might want to have the computer checked for codes even tho the check engine light may not have been on. Also have the alternator and battery tested again to see if something happened while in heavy traffic.

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Check that the idle speed is not too low in drive . Should be around 900 rpm in neutral and the idle speed is adjuste in drive to no less than 750 rpm. IT takes rpm for the alternator to charge the battery so if you have 11 volts then the car is runnung off the battery and not the alternator. It needs 13.5 volts to charge a battery and most regultors are set at 14 vvolt to 15.5 volts. If the vehicle is runnung from the battery as I stated then items like blinkers and stop light operation will show as fluctuations on the gauge. Have the system check . Make sure the drive belt to the aklternator is correctly adjusted as a slipping belt will also cause a problem.

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After i changed my alternator on my 2004 ford f150, my check charging system light and battery light comes on. also, my idle is really low now when i come to a stop, sometimes truck dies do to low idle. I...

sounds like a dirty plug connection somewhere, unplug what plug ends you pulled off and try cleaning the contacts inside plugs, good luck this should help

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Upon startup engine idles rough then speeds up and returns to normal idle .After a couple of minutes the volt light comes on then no power then a complete shut down.Starts back up for a while then shuts...

OK, the volt light means that the alternator is not charging the battery. It could mean the battery is shorted out, or the battery is bad or low on charge due to an alternator not charging.

Replace the Alternator and battery as indicated by standard voltage output tests under load.

The computer in the car will not operate the engine properly on low voltage.

Fixing the charging system, may resolve the rough idle (meaning that it may be trying to relearn after data was erased by low voltage of the battery), and the speed up.

Try the charging system first, and once that is repaired, reevaluate the engine driveability and speed and idle smoothness, after it relearns.

Good luck on this repair.

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Sounds like you have a typical case of loose fan/alternator belt or bad alternator.
If the belt is not tight enough with the engine idling the engine cant turn the belt fast enough on the alternators pulley, thus causing a low volts output from the charging terminal of the alternator, and this can cause all the funk you are describing. Put a test on the charging system, at least a 12volt DC digital hand held voltmeter across the battery terminals set it to 20 volts DC and let the car idle...if the voltage drops to 12.5 volts or less the belt may be loose or the alternator may be defective.
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Never attempt changing any electrical part like an alternator, starter motor, etc without first disconnecting the battery the alternator should come off with the removal of two mounting bolts, one thru bolt may be 5/8" hex or its metric counterpart 15mm hex at the alternators base(sometimes refered to as the "pivot" bolt) approx. 6" long, one belt adjuster bolt, either 1/2" or 9/16" or its metric counterpart 13 or 14 mm, one electrical plug easy clip pull type, and the out put wire has one nut either 3/3" or 7/16 " hex or its metric counterpart of #10 mm.
Be sure to clean the battery terminals using a baking soda mix and be wearing your eye protective googles.
Reinstall using the reverse proceedures and walla, you are back in business.
You may have to charge the battery before putting the vehicle back into service, and me as a ruke, i generally don't keep a battery longer then 5 years old, but that is just my theory, I don't want to get stuck during a road trip or bad weather or both having a battery problem because they erupt without notice at times.

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