Electrical problem - radio, gauge, battery light

[Jsheds]

Hi all, New guy here.

I have a 2003 Superduty with the 6.0. I started it the other day on a damp morning and could hear the belt squeak, it's never done that before. Headed for work and about 10 minutes down the road the radio quit playing, all the gages pegged at the high end, then dropped to zero and a few seconds later the gages were back to normal and the radio came back on. When I pulled into the parking lot I noticed the battery light flickering while it was idleing before I shut it down. It ran fine for the rest of the day. The next time I drove it the same thing happened. I also noticed that it seems like the heater fan slows down at stop signs and the lights dim a little, then go back to normal at speed.

I checked the battery ground cables on the block and frame and they are tight, but I didn't take them off to clean them. I pulled the battery cables off both batteries and measured 12.5 volts on each. I cleaned all the terminals and put the cables back on. When I turned on the ignition after re-connecting the bateries, the gagees pegged and the radio ejected a cassette tape that has been in there since the truck was new. With the truck running I get 15.5 volts on each battery. I checked all the ground wires I could find easily under the dash and everything looks good.

After searching the forums I saw a post from earlier this year where someone had the same problem, but no solution. Any suggestions what to look for? This seems to happen each time I drive the truck after about 10 minutes into the trip and then all is well except the battery light is now flickering more often. If the voltage on the battery is good, it seems that even if the alternator is going bad or the belt is slipping, the battery should give the electronics a steady enough voltage.

Thanks for any halp you can give.
Jim

 

[DaveBen]

If you are getting 15.5 volts, that is almost too high. 14.7 or 14.8 is the usual high end on the voltage. You may have an alternator problem. It could cause the funny electrical things that are happening to you. You should take off the alternator and have it bench tested by a good parts house or an alternator rebuilder.

Dave

 

[bigrigr]

X2 Daveben, 15.5 is to high

 

[Jsheds]

Thanks guys, I figured a bench test was in my future. Can anyone explain why an alternator would cause this erratic problem? I know it's all computer driven, is it the voltage fluctuations that flip out the computer?
Jim

 

[BIG JOE]

...... When you bench test yer Alternator (?) would also be a good time to load test yer batteries. If one (or both) went bad.. coulda been the root of the Alt. going south.. Maybe ??

Remember to test'm COMPLETLY disconnected from everything.

 

[DaveBen]

It is all tied to the computer. If it doesn't see everything just how it wants to see it, it will throw a code OR cause problems. The computer does not like voltage swings out of the normal range, which is something like 14.8 volts max. 15.5 volts is too high!!! You could damage the computer and that will cost you $$$ and time.

Dave

 

[BIG JOE]

It is all tied to the computer. If it doesn't see everything just how it wants to see it, it will throw a code OR cause problems. The computer does not like voltage swings out of the normal range, which is something like 14.8 volts max. 15.5 volts is too high!!! You could damage the computer and that will cost you $$$ and time.

Dave

X2 fer sure.

 

[JLDickmon]

Thanks guys, I figured a bench test was in my future. Can anyone explain why an alternator would cause this erratic problem? I know it's all computer driven, is it the voltage fluctuations that flip out the computer?
Jim

yes

 

[Jsheds]

I haven't gottena round to working on this yet, but I plugged a voltmeter into the lighter socket and ran the truck. At about 1200 RPM the voltage reaches 17+ volts and the entire dashboard shuts down, back to idle and everything comes back on. I'm going to pull the alternator this week and get it taken care of. Thanks for your help.
Jim

 

[dachshund]

Voltage regulator in the alternator is going south. And as stated above, have the batteries tested separately also. A bad cell can make the alternator work too hard or exceed it's duty cycle, so to speak.

Replace both batteries if one only one is bad.