Engine/Transmission (1994 - 1998) Gen Light on

[guldam]

Just got back from Christmas in Florida. Truck was parked for seven days in the parking lot and it started up just fine and dandy. But as it warmed up I noticed the GEN light was on. Looked at the volt meter and it was putting out about 12volts. I kept my lights off and all other stuff and drove the 42 miles back home with my fingers crossed. Truck made it home, where I checked the fuses under the hood and saw nothing burned.



Will clean terminals, though they were cleaned a couple months ago.



Tach and everything else is working fine.



We have had an awful lot of rain, and I wonder if another connection got water logged. I've had zero charging problems, and truck always starts with no pleading.



Short of pulling the Alternator, anything else I should look for?



GulDam

 

[chopperman]

My 97 did a similiar thing. After driving 65 miles to work pulled into to top off with fuel got back out on the road and had the generator light on. It was around twelve volts headed for just over 14 volts. I cheched grid heater relays no loose wires no burnt fuses left me a little confussed. I never have had a problem with the charge system before. I pulled the alternator off and had it rebuilt. I have not had another generator light on since. Check your batteries also and loose battery terminals. Happy New Year, Brian

 

[joet]

I had the same problem with my 96. I was leaving OR ant night and it was raining and I had gone about 50 miles and the gen light came on and the voltage was down. I was about 12 miles to a Love station so I keep on going and then the voltage came back up but the light stayed on. I got the book out at the Love station and didn't get anywhere with that, so I started it back up, the light was out the voltage was up. That was a year ago and no problem since. I rotated the batt every six months, so that was all clean.

 

[WilsonF]

Me too. It keep coming on about once about every couple of months. Finely got to the point it would not charge. I changed brushes and bearings but had to take it to a shop to find that the diode pack had burned out, replaced that and all was good. If you find that it is your alt. don't trade it for a rebuild have a shop rebuild it for you.

Floyd

 

[guldam]

Update:

This morning I go out to the truck and turn the key on, get the Wait to Start light. I wait, and the engine turns over (barely), but starts.



Gen Light is off. But Voltage is at about 11volts.



Have batteries on Charge.



Date on Interstate Batteries is March of 2008. They are 85 month batteries.



My battery charger has a built in Alternator tester, which I'm going to try out for the first time and see what it says.



Thanks for all the helpful feedback and suggestions!



GulDam

 

[guldam]

update number 2

Installed new / rebuilt alternator and truck is once again happy. We have no alternator shops nearby so I just bought one.



GulDam

 

[guldam]

Help! Update #3

This morning I start up the truck and notice that the idle is changing by about 100 rpms about every ten seconds or so, and with each rpm change the volt meter is changing a couple volts, and if my heater fan is on, that is changing in rpms. Scratching my head. Any ideas?

Edit:
Is this the Grid heater cycling on and off while the truck is cold? Normal? Didn't use to do this... .

GulDam

 

[WilsonF]

Yes, that is what happens when the grid heaters cycle on and off.

Floyd

 

[hsmith]

Sounds like normal operation at idle if the outside temp is 45* or less.

 

[guldam]

Thanks fellers... Evidently the alternator has been unhappy for quite a while...



But now it's working as normal. And yep, the ambient temperature yesterday morning was 36 degrees. Brrrr.



GulDam

 

[guldam]

Well, here we go again. Gen light comes on after about five minutes of driving. Checked all my connections, and the batteries are in good shape according to my charger. When Gen light comes on voltage drops to 12 or slightly less volts. But before the Gen light comes on it's up to 13volts charging.



This was a rebuilt Napa. I should have kept my old one, and had a good shop rebuild it.



Looking for a new alternator. Any suggestions?



GulDam

 

[hsmith]

If charging is your only issue, then go with a new Denso unit available from Larry B. I'm thinking Geno's may also have it. Are you having any problem with cruise, ac, etc?

 

[hsmith]

Just checked and the one from Geno's is not Denso, but PA Performance. Still a good unit at a good price, $249. New, not reman.

 

[KRStone]

Belt tight and seated right on pully?

 

[guldam]

If charging is your only issue, then go with a new Denso unit available from Larry B. I'm thinking Geno's may also have it. Are you having any problem with cruise, ac, etc?

Someone told me Denso is no longer available as New. Lot's of rebuilt units with a dismal record of not working, or not working for long.



Geno's has a PA Performance 136 amp alternator made in the US. Don't know squat about this brand.



Not sure what brand Larry's is.



Thanks,



GulDam

 

[guldam]

Belt tight and seated right on pully?

Yep, checked it twice. Checked battery connections, and wires to alternator.

Funny, I turn the truck off and start it up again, the light goes out, and I'm getting full charge. Then in a few minutes of going down the road, it stops charging and the light goes ON.

I loath to go back to Napa. .

GulDam

 

[GAmes]

Before you spend the $$ on an alternator, check to see if the intake heater relays are sticking closed. If they are, the PCM will kick the alternator off line after a few minutes of driving. Pull the small wires off the relays and give it a test drive.

 

[Missouri Mule]

You can check out the battery temp sensor (under driver's side battery tray) also,



Even though it was about time your original alternator to go out. (I just replaced my alternator this year. My mechanic put a NAPA but I still have the old one. Plan on having it rebuilt.



Guldam where were in you Florida?

 

[guldam]

Thanks, I will check that out also.



I was in Maitland to see my Mom, and then up to North of Ocala to see my in laws. Horse Country.



I lived in Orlando for 15 years. Can't hardly go back to the heat and humidity any more. I do however miss the fresh water and salt water fishing. Also miss Skycraft.



I sure wish I'd kept my old original alternator. No more refurb starters or alternators.



I did keep my old starter, and plan on rebuilding it.

You can check out the battery temp sensor (under driver's side battery tray) also,



Even though it was about time your original alternator to go out. (I just replaced my alternator this year. My mechanic put a NAPA but I still have the old one. Plan on having it rebuilt.



Guldam where were in you Florida?

 

[guldam]

Thank you sir, I will try this shortly.

Before you spend the $$ on an alternator, check to see if the intake heater relays are sticking closed. If they are, the PCM will kick the alternator off line after a few minutes of driving. Pull the small wires off the relays and give it a test drive.