Engine/Transmission (1994 - 1998) Generator overcharging

[ejtaintor]

On my '97, the Gen light came on and the voltmeter was reading a bit high. I grabbed my multi-meter and checked at the battery and it's sitting anywhere from 14. 7-15. 1 volts at idle. When idling with the lights on, they have a slow flicker but it goes away with minimal rpm increase. I have changed the voltage regulator (external mod) and checked another generator all with the same results. Not really sure where else to look. Any thoughts?

 

[B.G. Smith]

The lights flickering is probably caused by the voltage regulator. After the truck has run for a while is the voltage still above 15 volts? could be a faulty ground between the truck body and the alternator/engine. The control voltage should be around 13. 9 to high 14's, even 15 on startup cold. bg

 

[BLNRAY]

ck your battery,bad cell can cause voltage increase. also make sure your grounds are good

 

[Skydiver]

Is your "Gen" light staying on? As I always say "test your testor". Make sure your volt meter is correct.
BLNRAY is correct. Check & clean the simple things first, including both sides of all battery cables.

 

[DieselDoghouse]

What BLNRAY said and remember: bad cell means 1 of 6 PARALLEL 12V cells is not (reliably) connected - makes your battery appear smaller—could make weirdness happen - have you battery(s) reliably load-tested.

 

[B.G. Smith]

What BLNRAY said and remember: bad cell means 1 of 6 PARALLEL 12V cells is not (reliably) connected - makes your battery appear smaller—could make weirdness happen - have you battery(s) reliably load-tested.

Good point, bad cell will cause strange problems, just so we don't get too far afield, the six cells are 2. 11 volts each (hopefully) and are connected in series. bg

 

[ejtaintor]

The light is staying on from the minute the generator fields until I shut it down.



So if there is a bad cell, does that mean there is basically supply but no demand so it comes across as excess voltage? My red tops are 6+ yrs. old so there is definitely a chance they are bad. They still crank great so I hadn't suspected any issues with them. Just trying to narrow it down before dropping $300+ on batteries.

 

[ejtaintor]

I threw a couple of ground jumpers on (1 from body to batt -, and 1 from the gen. mount to the batt -) and still no luck. Need to see if I can get my hands on a load tester and see what the batts. look like.

 

[WilsonF]

Around here Les Swab and Wal-mart will load test free.

Floyd

 

[ejtaintor]

Pulled the battery leads while it was running and no change. I'd guess it's not the batteries. I ran a ground from the external regulator to the battery and it reigned it in just a little bit. At this point because it's keeping it between 14. 7 and 15 volts, I'm thinking it's a bad regulator as it seems to be regulating (it's not spiking to 18 volts), just not enough.

 

[ejtaintor]

Bringing this one back up. Still haven't found the fix on it. I added a ground from the voltage regulator straight to the battery and didn't see a change. Batteries got swapped out as my old Optimas were about 7 yrs. old. Threw a new voltage regulator on over the weekend just to see if the past 2 have been duds. I got the more expensive one from NAPA as the last 2 have been the cheap version and still no luck.



Didn't mention this previously but as the truck is idling after the Gen. has phased and without the AC pump running, about every 30-45 seconds the motor will pull down a hundred RPM or so and the voltage will drop with it. It is like when the AC pump cycles but again the pump is not on (AC or Defrost).



Any other thoughts would be greatly appreciated.

 

[fest3er]

Run the truck up to 20MPH once, then see if the periodic dip is still there. The intake heaters are the only thing on the truck that will normally drag down the RPM and voltage.

Find someone with an oscilloscope to look at the output of the alternator. You should see only 'humps' (top of sine wave); if you see any 'flats', you have a dead diode.

FWIW, 14. 7VDC is not an atypical charging voltage.

That all said, more than likely you have a poor connection somewhere (ground or power), one that handles low current fine, but heats up and conducts less at higher current.

 

[ewcmr2]

Warm up the battery temp sensor on see if the voltage goes down. Maybe it's just cold where you are and the PCM is asking for more juice.

 

[ejtaintor]

The surging happens both at start-up and after it's been driven at speed. Pretty much always at idle. I don't believe it's the batt. temp. sensor. The coldest I see here is high 20s and 110+ in the summer. ambient temp doesn't change anything.



I don't really have an issue with the voltage hitting mid 14s, I just don't like it scratching at low 15s.

 

[Missouri Mule]

If your using a external voltage regulator I doubt that the battery temp sensor is hooked up to it. The battery temp sensor is hooked up to the Internal voltage regulator/EVR (Electronic Voltage regulator).



I pull your alternator/generator and have it tested.

 

[muchsnow]

Was this ever fixed???? Same prob here...

 

[Missouri Mule]

muchsnow, what are your temps there? Did you put external regulator on (by-pass the internal regulator(EVR) in PCM)?

If not and it is rather cold there your battery temp sensor is telling the EVR that the battery is cold so the EVR will raise the voltage. When the batteries are warm the EVR will lower the voltage (will have to look up voltage output in FSM).



Light flickering could be ground,broken wire, loose connection, or bad light switch. If your having that problem.

Second thought, grid heaters can be going on when lght flicker but volts would go down to 12 volts (if volts are at normal reading of 14 volts).



Looked at FSM no mention of volts per tempature readings.