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Alternator doesn't start charging until battery is

alternator doesn't start charging...

alternator doesn't start charging until battery is completely dead

Mechanic's Assistant: Did you test the battery with a voltmeter? And have you ever changed one before?

Battery was just tested and passed at the dealership

Mechanic's Assistant: What is the model/year of your Ford?

2006

Mechanic's Assistant: Are you fixing your vehicle yourself? What have you tried so far?

New alternator, tested the battery

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Answered in 5 minutes by:
3/17/2018
Michael
Michael, Ford Senior Master Technician
Category: Ford
Satisfied Customers: 670
Experience: Ford Senior Master Tech w/22 yrs exp.
Verified

Hello, my name is Michael. I will be assisting you today.

What model is your 2006 Ford?

What symptoms are you having?

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Customer reply replied 5 months ago
F150 The electrical system analog gage in the instrument cluster continues to fall while the engine is running, once it gets to it's lowest point or near there, the needle suddenly shoots up to about 13-14 volts (I'm assuming that's the value, the needle actually goes up to a bit past the middle of the gage) and the battery starts to charge.

Have you noticed the red battery light coming on, or any starting problems?

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Customer reply replied 5 months ago
The engine will not start unless I have run it for a good long time while the needle is in the high position. I've never seen a red battery light in the dash, I'm not sure there's even one there.
I have hooked a multimeter up to the battery and across the alternator. The DMM confirms the reading on the needle. I think that the PCM is controlling the charging system and it (the PCM) is faulty. I replaced the alternator and it worked fine for 3 weeks before going back to it's evil ways. Brand New DuraLast alt. The Ford dealership near me tested the battery as it is a motorcraft battery and is still under warranty. It tested good

I suspect you have a bad alternator. You are correct that the PCM controls the charging system. It watches the load and then adjusts charging based on need. There is a big problem with aftermarket alternators in Fords with the PCM controlled charging. I have a 2004 and a 2008 Ford. One Expedition and one F-150. I've had to replace the alternators in both. In both instances it took two or three alternators until I found one that worked. The aftermarket voltage regulators do not work properly with PCM controlled charging. Although it's not setting a warning light I don't think your alternator is responding to the commands from the PCM properly.

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Customer reply replied 5 months ago
Is it possible to temporarily disconnect the pcm from the alternator thus tricking the alternator into constant charging? I noticed from the schematic that the three wire plug into the voltage regulator are marked gencom, genmon and I think the third is ground.
Customer reply replied 5 months ago
I just need it to run until I can get the new alternator and find the time to install it.

The alternator needs the voltage from the third wire to charge normally. However, if you disconnect the connector and hold the engine at wide open throttle (about 4,500 rpm) for three seconds it will cause the generator to self-excite. At that point it will maintain 13.5V until the engine is shut off as long as the generator itself is working.

If I can be of any further assistance do not hesitate to ask. If not, please rate my service. If for any reason you feel you cannot rate my service five stars please let me know.

Michael
Michael, Ford Senior Master Technician
Category: Ford
Satisfied Customers: 670
Experience: Ford Senior Master Tech w/22 yrs exp.
Verified
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