98 Durango 5.2, Altenator quit working and so I took it and had it checked, it shows 15+ volts on machine. Put it back on truck it works for a few days and same thing all over again. I keep having it checked but it always shows that its charging good and when I put it back on truck it works for a few days. I replaced the PCM and still had no alt so I started tracing wires and checking grounds. Everything looked ok and I saw no problems so I took a chance and tapped on the alt with small hammer, it kicked on. I replaced the altenator today and when driving to work it spiked, charging almost 18volts, blew headlights, driving lights, and dash lights. What should I check next?

Thanks
Mark.

 

15+ volts on a alternator is too much output. It should be around 14.3-14.6 maximum. There is an internal regulator built into the alternator that is supposed to keep your final output in the 14.3-14.6 range. Anything over that is a bad regulator so you replace the alternator.

The PCM only regulates the voltage to 12 volts to go into the system. Simply put your PCM is fine and doing it's intended job.

The head lights are on the battery side so there is more than 12 volts (14.3 volts) so when your alternator went to 18 volts, well that is the reason they blew (to many amps).

Countless times I have seen bad alternators right out of the box. Try to only buy NEW alternators and not remanufactured (rebuilds). Course that is hard to obtain so at least get a rebuild with a life time warranty.

The next thing that I am going to bring up is the battery. Concerting the battery is in a direct line with the alternator I always replace the battery whenever I replace the alternator. Many times the alternator is taken out buy a bad cell or other reason because of a bad battery, or the alternator will overdose the battery causing the voltage to back up into the alternator and burning your cells in the battery.

I like Auto Zone as my favorite (but each to their own). Auto Zone Duralast Gold series batteries have a 8 year warranty! And their alternators are good and I haven't had an issue with them. My recommendations would be pull that alternator out and take it back and describe that it has a bad regulator in it as it went to 18 volts and get your money back. Go to Auto Zone and get a Duralast Gold series battery and a Duralast alternator and get a $2 dollar battery post and terminal brush combo, clean the connections and buy the acid rings $2, and a spray coating $2 then get home and first clean the terminals.
Reset the PCM.
Then install the alternator.
Then install the acid rings on the battery.
Then install the terminals and tighten.
Then spray the terminals with the ant-acid coating.

Follow the rest of the PCM reset instructions.


Also, if you just want my opinion then just send me a PM (like you did) or post it as general and if I see it and know an answer then I will post. Otherwise just send me a PM.......

 

Took the altenator back to autozone and had it checked... They couldn't get it to produce more than 10 volts so they ordered me another one. Supposed to be here today around one.

 

That's what I thought, bad alternator! Replace the battery as well.

 

New altenator, new battery, same problem... Taking to stealership in the morning. Don't know what else to do.

 

You have to look at the output at the battery.

Now the PCM controls the main voltage to the inside electronics including engine, however the battery is NOT regulated other than the < 14.6 voltage at output from the alternator. This is why the battery charges. The battery must have about 14.3 volts to fully charge whereas the rest of the system only needs 12 volts and is mainly regulated by the PCM.

99.9% of charging issues is the alternator or battery but there is always that .1%. There is only 3 parts to the system:

1. Battery
2. Alternator
3. PCM

The only way you could get the same consistency (ensuring everything is tight and clean and working as intended) as you describe is if the 12 volts from the PCM to the diode bridge (which converts AC to DC current) is bad and/or inconsistent.


Please keep us updated on your findings!

 

Well I replaced the ECM again, under warranty, and now the new one doesn't recognize the overdrive. Everything else works, just O/D OFF light on and button will not turn it on. Another ECM?

 

ecm is the ford unit, dodge has a PCM and it does sound like it if all was well before you changed it.

 

Get a new one if the OD was fine before. You should be able to plug in your other PCM and ensure it works then you know it's the PCM.


I have seen people go through 3 PCM's before. Sometimes the companies don't actually send one that matches your year and that will screw it up as it will plug in and all, but will have strange issues like you describe. Give em a call again and sorry but it happens more times than ya think so your not the only one.

 

Got the new ECM today and so far everything works like its supposed to. Gonna drive it to work tonight and we'll see what happens.