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Alternator problem, please help

8K views 21 replies 6 participants last post by  Capt. Obvious! 
#1 ·
Why would an alternator only work when the voltage regulator is unplugged[scratch]


When the car is running and the voltage regulator is plugged in with the three wire connector on the back of the alternator it does not put out any voltage and the battery voltage drops to 11.92v. There is no indicator light on in the dash, but both my DVOM and a Snap-on battery/alternator tester confirmed the alternator was not working with the voltage regulator plugged in. I checked continuity from the alternator all the way back to the pcm on the gray and blue wires and they both had a good connection and the red wire had good continuity and voltage.
If I unplug the voltage regulator the Snap-on tester showed the alternator as good, but the indicator light on the dash lights up.

All I can think of is maybe the PCM needs reflashed or replaced??? It does have a custom tune by FSWerks for the supercharger. Is this a likely culprit???

I'm at a total loss, please help!!!
 
#4 ·
Called FSWerks, they assured me that it is not possible for the tune to fail and cause this. They explained that it would not work at all if it failed. They suggested faulty wiring, but I've already tested everything that I know how. If you guys have any tips on ways to test it, please let me know.
 
#5 ·
Electrical gremlins are terrible, you may have to check each individual wire from battery to alternator . And do a process of elimination. If this has just started since you put the supercharger on. Start checking wires around any of the connections with it. And check close to anything that maybe around the hot exhaust.
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#6 ·
It's had the S/C for years and it has no electrical connections, this problem just came up recently. I'm beginning to think corrosion in the wiring harness I'm going to try load testing all the wires from the alternator harness to the PCM and fuze box tomorrow. Just to see if maybe they have continuity but are too weak to handle a load. I really don't have any idea what else to do. I think when I move back to the US in May, I'm going to buy an old 60's-70's pickup so I don't have to deal with this stuff anymore.
 
#7 ·
When I changed my alternator out I went ahead and upgraded my ground wires and also upgraded my wire from the alt to battery. As a safety measure and for piece of mind since I have a lot stereo equipment.
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#9 ·
ECU W/ custom tune replacement questions

Why I think I need to replace it
After much diagnosis and trouble shooting, I've come to believe that my ECU is shot. It appears I no longer am getting signal to my voltage regulator telling my alternator to charge. I've checked continuity and voltage drop on every wire related to the charging system. I've replaced the alternator twice and the battery once. Checked every ground under the hood and cleaned and tightened every connection on them. I've done every bit of diagnosis I can do that I know of without an oscilloscope or access to the Ford PID's. Nothing has changed the results. The only thing that has worked to allow the alternator to charge the battery is to disconnect the wire harness from the voltage regulator. This allows the voltage to go to 13.8v (with the engine running) opposed to 11.9v with the regulator plugged in.

What I think I want to try
I want to try replacing the ECU if I can find one to see if that fixes it, But I need to know what I will need to do to flash the ECU. I have the SCT flasher unit with the current good tune on it (yes I even tried reflashing it). Will I be able to use this to flash the new ECU or will I have to buy an additional program or something to make it work? I'm afraid it may not mate to the new ECU since it's already been use on the one that's in the car. I'm not sure if the SCT units work like that or not.

The ECU connector has "LUY4" written on it. Is this the number of the ECU I would need to buy?

Other options
My last resort is to rig up an older style system somehow. Either using this alternator with the regulator disconnected and using an external regulator, or even an older style alternator with external regulator. this will however turn on the indicator light on the dash, which I would like to avoid.
 
#10 ·
You need to find a pin-out chart for the signal wire from the PCM. You should also try to find the values for the correct voltage you should see under normal operations to further confirm it's the PCM before you spend all that money!
 
#12 ·
I have the pin-out, (pin 72 and 59) I don't know for sure what the voltage should be. I read somewhere it should be battery voltage on the red wire, 9v on one of the others (blue iirc) and zero on the last one (which I have). But I cant find where I read it again.

Besides that, I believe it needs more than just voltage, it requires a specific signal from what I've read. I could be wrong though.
 
#13 ·
I think the alternator control works on PWM pulse width modulation. When there is a demand for current then the pulses are wide. When the demand is low, then the pulses are narrow
Having said that, to replaced the ECM, you also need to program the PATS, so you need to go to Ford. Unless of course you find a ECM in a junker with a key
 
#18 ·
I'd be looking at continuity of the grey wire, in particular. The problem would seem to be somewhere in your wiring harness. Have you tried using a temporary duplicate wire i.e. wired up something outside the factory harness?

P1246 - Generator Load Input Failed
The PCM monitors generator load from the generator/regulator in the form of frequency. The frequency range is determined by the temperature of the voltage regulator where 97% represents full load, below 6% means no load.
Causes:
Generator circuit short to GND
Generator circuit short to PWR
Generator circuit open
Generator drive mechanism
Damaged generator/regulator assembly
Damaged PCM
Verify battery voltage is 14.5V.
Verify generator/regulator has the correct part number.
 
#19 ·
I checked the continuity of all the wires between the plug at the alternator and the plug at the PCM and the battery junction box. All were very good (0.1 k ohm). I'm going to tear apart the extra alternator I have to see if I can find a fault internally. Might have to make some sort of rig to test it. Also going to try to get into a dealer and see if I can at least get a diagnosis.
 
#20 ·
Well, I found the problem. The PCM is not giving the voltage regulator the right signal. On top of that the alternator is also no good. Fortunately I found a solution that does not require the PCM being replaced.

First, I will be returning the bad alternator for a replacement. Then I will be replacing the stock F601 voltage regulator in the new alternator with a F600 type regulator. this regulator does not need the PCM to control it. It uses a 14.8v constant set point and only requires a wire that is hot with the ignition on and a sensing wire going to the output terminal of the alternator. I also bought a pigtail for the wiring harness to plug into the regulator so I don't have to cut up my factory harness.
 
#22 ·
I'm getting the F600 style. The F601 style is what they have stock, these require the signal from the PCM where the F600 does not. You can just google "F600 voltage regulator" to find more info

This is the one I ordered
http://store.alternatorparts.com/t9...tage-regulator-for-6g-series-alternators.aspx

It is basically a really heavy duty version of the F600, You can find them cheaper if you shop around, but this company helped me find the info I was looking for so I bought from them.

Be aware that this is a rare problem, and the solution I provided requires custom wiring so it's probably a good idea to make sure that this is really what you need. The dealer I took my car to in order to get the PCM diagnosed said this is only the second Focus PCM they have ever seen fail and they've been around since well before the Focus was ever thought of.

99.9% of the time if you are having a similar problem, it is the result of the PCM connector going to the alternator/regulator. Wires in these are notorious for breaking. Some alternators even came with a new pigtail at one time.

I would suggest looking into this first.
http://store.alternatorparts.com/partnowaa600.aspx
 
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