Charging system woes

[theoldwizard1]

With the engine running, measure the voltage at the alternator output stud and the alternator case. If you have 13.5 - 14.5vdc that alternator is fine.

If the PCM is controlling the voltage of the alternator (I do not recall what year that started) then, if you have a nearly fully charged battery, shortly after starting the voltage at the battery (which should be identical to the voltage at the alternator output stud) will drop to about 13.2V within a minute or 2 of starting.

 

[theoldwizard1]

Replacement connectors with pigtail (so that you can splice into an existing harness) are available. Check the Motorcraft Wiring Pigtail Kit Identification Guide.

 

[Big Brian]

nice link Wiz!!

 

[Red88LX]

That's great. Thanks Wizard.

 

[sjwelds]

nice link Wiz!!

Concur!

 

[theoldwizard1]

From post 16 of http://www.expeditionforum.com/threads/2004-expedition-2-4l-check-charging-system-message.33535/page-2

Apparently the previous 2 alternators were rebuilt alternators but the 3rd was a completely new one. The mechanic said that he's seen a lot of the rebuilt alternators do this. Not just Ford but all brands.

This is the mechanics opinion but he's been a mechanic for over 30 years so he should know a thing or two.

He said that "all the newer cars with computers are very particular with the fluxuating voltages and amperage and more-so than the older non-computer controlled cars. The alternator has got to produce exactly what the pcm wants to see or it doesn't like it. "

More specifically, both the voltage regulator (inside the alternator) and the PCM measure the battery voltage INDEPENDENTLY ! Even though the alternator/voltage regulator and the PCM "talk" it is a very "low level" communication (kind of like "baby talk"). The short story is, the alternator/voltage regulator tells the PCM if the battery is low and then the PCM (after checking a buch of other thing) will tell the alternator to charge.

If you want the GORY details, watch this video Ford "Smart Charge System" Alternator Not Charging

 

[blue oval guy]

send back and install a Motorcraft alt.

 

[riverside]

Hello folks, I finally got a chance to get out and mess with the Expedition again.
What I really need to know, which connector is the C175b? So I can test that portion of the wiring (I have good continuity from the alternator plug to the C192 connector).
What I did do was backprobe the C192 connector and took a reading of both the 1930 and 1931 leads with my ancient Matco Diagnostic analyzer. With the engine running the 1931 lead, the one sending a signal to the PCM was fluctuating between 0.1 and 0.3 pulse width, I couldn't find the manual so that is either seconds or milliseconds, either way some kind of signal is being sent. the 1930 lead was completely dead.​

 

[theoldwizard1]

I think C175B is the PCM connector. I think on your vehicle the PCM has 3 different "pockets". I don't know how the pins are numbers.

Attached is a wiring diagram from BBB Industries TSB's & Wiring Diagrams web site for a 2003 Expedition 5.4L, Engine System, Charging Subsystem.

Watch the video I linked before. The PCM will not start "requesting" output from the alternator until a few seconds on 1930 (also called the "Generator Communication/GenComm" link) after the engine starts. If that wire could appear to be dead it could be because the microprocessor INSIDE the alternator is not providing a positive pull up voltage on that wire (it is pulled down by the PCM; see attached diagram).

1931 is the called the "Generator Monitor/GenMon" link. Positive pull up voltage is supplied by the PCM and the alternator does a pull down.

If you don't understand what I am talking about the forget trying to diagnose it further. I don't know what a Matco Diagnostic Analyzer is, but you really need a 2 channel scope or at least a good DMM that read pulse frequency and width (%) to get to the root of this problem.


I am hesitant to suggest this, so AT YOUR OWN RISK, cut the 1930 wire. Use a standard 12V test light with the tail connected to ground and check to for voltage on 1930 AT THE ALTERNATOR ! Use an incandescent (not LED) test light, not a DMM. (If you don't understand why, you have enough experience doing on vehicle diagnosing.) My "gut tells me this is your root problem (no voltage on 1930 from the alternator). Cutting the wire proves that the PCM is not "loading down" the circuit.