ET RAM

Yesterday my Gen light came on. I checked the battery voltage with engine running and it is a 12.96V so alternator is not providing a charge. A search here has given me a few tests that I will try to do this morning.

I would like to know if there is a good alternator shop in Kissimmee-S. Orlando that can check this for me. I had planned to leave for Texas this Sunday so I do not have much time.

One last important question. My batteries are new. So, if I do a good charge on them, can I drive to Texas as is? My truck is not all electrical. Once started, I believe the batteries will run some sensors, PCM, the gauges and clock. If someone knows of any major battery drain please let me know. I purchased a battery charger to charge before leaving and to use enroute if needed. I will check battery voltage along the way to monitor.

This is kind of desperate but I need to be in Texas Monday. It will be about a 15 hour (daylight) drive. Another idea is to do a 2 day drive and stop and recharge at a motel. That may be best. Any thoughts on this will be appreciated. Thanks

ET RAM

Well, I did some troubleshooting today using the following info:

dozer12216
Registered User Join Date: Dec 2007
Location: North Carolina or Kentucky. Take your pick
Posts: 2,314

Humor me!
The two small wires connected to alternator.
One is battery voltage when running.
The other is field control through the PCM.
Take a 5 amp fused wire and ground the field control wire for a few seconds.
Alt out put should hit max. You should hit 15 volts at battery.
If you don't. The alt is bad. The bat wire is bad. The voltage supply to field is not functional. The belt is slipping. You figure.
If it does charge. The wire from alt to PCM is bad. The PCM is bad. You missed something in wiring check.
charge-y Charge-y
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I checked all the fuses with a meter. I had good continuity on the alt to battery feed wire. I had battery voltage at the alt feed terminal. With engine running I had battery voltage at the small + stud back of alt. I tried grounding the field wire but did not get any charging. The belt is good and not slipping. So this seems to indicate a bad alternator or a bad field wire or PCM. This is the original alternator so it just may be worn out.

I am taking the alternator to have it bench checked. Anything else I can check. How would one check the field wire and PCM if that is the problem? Thanks

patdaly

Here is a good way to check your Alt, posted by someone on here, sorry I do not have the original posters name for credit.

"I had to troubleshoot my charging system recently and came up with a fairly simple way to isolate the problem. Here is a step-by-step way.

First you will need a DVM to measure voltage. Also the batteries need enough charge to start the engine, so use a battery charger to get them charged enough.

The charging system is made up of the PCM mounted on the firewall, alternator, and don’t forget the 120 amp fuse in the PDC on the driver’s side fender well.

1) Start the engine and measure the battery voltage at one of the batteries. It should be more than 13 volts but probably less with a charging problem and that is why you are here.

Measure the voltage at the alternator output terminal (B+) leaving the DVM negative connected to the battery negative post. It the measurement is greater than 13 volts then the fuse in the PDC should be checked or the nut holding the heavy gage wire on the alternator is loose.

If you get this far then the next step is to measure the voltage coming from the PCM. The two small nuts on the back of the alternator are the ones to measure with the lower one positive and the upper one negative. These are the field terminals on the picture. If the voltage reading is greater than 8 volts the PCM is calling for full charge and your alternator is bad and not putting out. If the voltage is less than 3 volts your PCM is toast or the wiring between the PCM and alternator is broken. The normal voltage reading at the field terminals will vary from 3 to 6 volts when working correctly.

It’s always a good idea to clean battery terminals and check for bad grounds before spending money on replacement parts.

My alternator turned out to be bad and I had 9 volts at the field terminals. It was the diodes inside that were bad."


BTW, whenever I run into a really good post explaining something, I save it to a Word file and keep it on my jump drive in the truck. That way, if I am in the middle of BFE I still have most of the info I need...... Just a thought.

ET RAM

patdaly,


Thanks for the reply and that info post. All my testing was pointing to the alternator. I took it to Auto Zone and they bench checked it and it did not pass. So, I purchased one there. It is now installed and charging the batteries. I just hated to give up my original core. Rebuilding it would have been my preference. If I were at home that would have been the route I would have taken.

Just info for those who may purchase a replacement alternator. Check the pulley to make sure it is the right one. After I had installed the new alternator I found that the pulley was not the right one. So, I had to take it off again go back to Auto Zone where we exchanged pulleys.

Any way, thanks again