Alternator charging issue

[davydude]

Would like to know if replacing the PCM/ECU would allow the alternator to charge when all else has failed? Voltage drop on Pos and Neg side were good. Or would wire sending info be more suspect? Between Alt and PCU. Do they sell such a wire? An otherwise great running 4.0 v-6 since 1999 has started a bad habit of killing batteries mostly when running. Never an overnight kill, only when running. A battery which is over rated will allow it to run much longer, but will still kill it.

 

[96eb96]

PCM has nothing to do with the Charging system. What is the voltage when the car is running and accessories such as lights and blower motors are on? If it is below 13.XV, suspect the alternator.

 

[Tech By Trade]

The charging system is not controlled by the ECU. there is a hot wire, gnd and a remote line that control the alternator. Have a real close look at the remote line and fusable links on the batter/alternator harness. I believe the remote feed is taken off before the first fusable link, and it has a fusable link in it as well. The complete harness will run you around 100 bucks on rock auto. It feeds the starter, alternator and battery. That is only if you have tested the alternator and know its functional, and you have a good known battery. If its discharging the battery when running, odds are its a bad diode pack in the alternator. If its just not charging, check that remote wire.

 

[koda2000]

Does your BATT/CHG light on the dash work? If the bulb is burnt out the alternator will not get turned ON.

Check for voltage on the "B" (large terminal) on the back side of the alternator with engine running/accessories off. If no more than battery voltage the alt is not charging. Remove it and take it to the auto parts store for testing.

 

[Mbrooks420]

Probably a bad connection or partially failed alternator. No matter how big your battery is if the alternator isn’t putting juice to it your truck would only run a few minutes.

 

[BrooklynBay]

What is the voltage of the system while it's running?

 

[davydude]

A few things I forgot to mention. Did start this anomaly on old alternator which was stock and probably good, new alternator did same thing immediately and has been removed and bench tested as good. Battery light comes on key on but not while running. Because battery is disconnected frequently Engine code light isn't always on. When it does, no battery light and codes are only showing o2 sensors p0171,174 but nothing about charging system.

 

[davydude]

Voltage when running 11.9 gotta go to work. Best (correct) answer by end of day wins!

 

[Mbrooks420]

You have a cable issue, or a bad alternator. Ohm out your cables.

 

[BrooklynBay]

Those codes show that there might be an issue with the intake manifold gaskets. Check a schematic diagram of the charging circuit, then follow the color codes of each wire, and check with a continuity tester.

 

[koda2000]

A broken wire or bad connection? Did you test voltage at the "B" terminal? If same as at battery alternator is not getting switched ON. If 14+ volts at the alternator it's not making it to the battery. Have you replaced the electrical connector at the alternator? Fusible link, broken wire or blown fuse.

 

[Tech By Trade]

https://www.rockauto.com/en/moreinfo.php?pk=610504&cc=1354542&jsn=463

 

[Mazior R.]

If its the alternator going bad, you could always move the brushes up or buy new ones for around 5 bucks if thats the case.

 

[BrooklynBay]

https://www.rockauto.com/en/moreinfo.php?pk=610504&cc=1354542&jsn=463

It said that it's the last one on their website.

 

[koda2000]

https://www.rockauto.com/en/moreinfo.php?pk=610504&cc=1354542&jsn=463

That looks pricey. I'd spend quite a bit of time checking the wiring before giving up and purchasing that. Nice to know the whole thing is available though.