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Discussion Starter · #1 ·
My focus left me stranded for the first time a few weeks ago. The alternator stopped charging. I had it towed home and removed the alternator. Went to autozone who put it on their tester and it tested with no voltage output. It was under their warranty so they gave me a replacement. I put that in and I am still having problems. I have a obd2 gauge in the car so I monitor voltage on it. Here are the symptoms:


9 times out of 10 it starts up and runs fine. Charges at 14-14.1 volts. Holds voltage good with all the accessories on including the lights and rear defog.

Occasionally on startup it fails and is not putting out voltage.

If it works on startup then randomly while driving it will all of a sudden lose charging.

Sometimes after a while the charging comes back. Sometimes it stays in fault condition. Sometimes when in fault condition if you shut the car off and then start it back up it starts charging again.

Here maybe a key to this puzzle:
When it goes into this failure the #10 fuse under the hood blows. This is normally a 1 amp fuse. Supposedly for the voltage sensing circuit. I have put a 10amp fuse in and it still popped it. The car does not appear to need this fuse for charging. If the error conditional does not exist the car will charge whether this fuse is installed or removed.

When it is in error condition I have aggressively wiggled all the wires in the wiring harness including the pigtail and it doesn't bring it back. I am 99% sure I replaced the pigtail a few years back as I see blue electrical taping up the harness.

So what could blow fuse #10? Any ideas on this situation? I appreciate any help in advance!
 

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F10 is a 1-amp fuse on PZEV cars & is a 10-amp fuse on non-PZEV cars. So I will assume you have a PZEV. No need to use a 10-amp fuse anymore... as you work on finding the problem.

F10 is uniquely isolated. Unlike many other fuses, this one only provides power to the Alt; because of this, it makes it easier to hunt down where your (intermittent?) "short" is coming from. The power path of F10 takes it directly thru the pigtail splices. I would un-tape the splices, inspect, then REPLACE the splices or replace the splices -and- the pigtail.

Pigtail;
http://www.summitracing.com/parts/pco-5716pt/overview/

A defect inside your new Alt can cause F10 to blow. I'm not sure, but there is a very good chance that the PZEV Alt is different than non-PZEV cars. Please consult your local Ford dealer or similar type persons to confirm. You might have the wrong type of Alt in your car.

Your VIN does not have a digit-code to tell you if your car is PZEV or not.
 

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'A defect inside your new Alt can cause F10 to blow.'

Very possibly.............new alt, new problems there. Rebuilt alts have the same quality as your McDonald's burger now, i.e., don't be surprised if the burger doesn't even have any meat on it, the quality is abysmal. The alt can pass testing and still be bad.

If pigtail changed a way back entirely possible weathering has flawed the integrity of the connections if only crimped but not soldered. Meaning do-over time.
 

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Discussion Starter · #4 ·
It is a pzev car. The alternator I just put in matched the alternator that came out. And the alternator I replaced years ago was a oem one. So I am confident I have the right part. However, it wouldn't be the first time I got junk from AZone. Ha! However, when it died and I had to have it towed the fuse was shot then too. While that alt tested bad I wonder if because of the shorting situation it caused the problem with that alternator. From looking at a wiring diagram I see two control wires going to the pcm and the third is the red wire that is suppose to run to that #10 fuse right? That being the case the question is the two wires the run to the pcm, are they strictly low voltage data or do they carry the full current of the redwire back to the pcm? I am thinking the easy fix (assuming my connector still passes inspection) would be to snip the redwire connection at the pigtail and put in a fuse holder with a 1 amp and then a ring terminal and just bolt it under the charging cable that runs to the starter. Then it pulls power from that. If the fuse still blows then the short is in the cables going to the pcm and thats probably a can of worms that I may not have time to tackle myself. The other question is why does the system still charge if the #10 fuse is removed?
 

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From looking at a wiring diagram I see two control wires going to the pcm and the third is the red wire that is suppose to run to that #10 fuse right?
Right.

the question is the two wires the run to the pcm, are they strictly low voltage data or do they carry the full current of the redwire back to the pcm?
My wire diagram offers very little or No info on design & operation; and is not a "function diagram". My guess is; power from F10 is completely independent of what the 2 PCM control wires are doing... Independent and yet dependent... So, also guessing that without power from F10, the PCM would be unable to regulate Alt output power/voltage.


I am thinking the easy fix (assuming my connector still passes inspection) would be to snip the redwire connection at the pigtail and put in a fuse holder with a 1 amp and then a ring terminal and just bolt it under the charging cable that runs to the starter. Then it pulls power from that. If the fuse still blows then the short is in the cables going to the pcm and thats probably a can of worms that I may not have time to tackle myself.
I wouldn't call that the easy fix, but it is creative. I do not agree that "if the fuse still blows" that the fault is within the wiring that goes to the PCM. My guess is the fault lies within the Alt or the wire/pigtail splice that goes to F10.

The other question is why does the system still charge if the #10 fuse is removed?
Good question. I would have guessed that the system would fail if F10 was blown. But going back to what I said earlier-> ... "So, also guessing that without power from F10, the PCM would be unable to regulate Alt output power/voltage." Maybe the Alt still works, is still providing power, but with F10 blown, the PCM is now unable to adjust the Alt output. Seems like that would set a DTC or maybe turn-on the BAT caution light on the dash. Have you had your car scanned for codes while F10 is blown?
 
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