Hiya everyone, been reading good forum info here for years (thanks for that!) but now I got one that I wanted to ask about.

Got a '99 F150 5.4L with about 230k miles on it. Was driving it when radio went out, then couple miles down the road the gauges started acting funny. Was coming into rain storm so tried wipers (they were very slow as I suspected) so pulled off to parking lot. I figured battery or alternator issue. Next thing I knew, all power came back to truck and appeared normal. Not trusting this, I sat in lot at idle. Couple minutes later gauges died again and lights went out. Sat in idle for 15 minutes mentally troubleshooting when truck died.

So...took battery to get tested. I read 35% charge with bad cells, replaced battery with new off shelf. Checked voltage of battery new - was 14.6. Put in truck and started it, voltage at battery was now 17.4. Limped truck home, stopping at auto parts store to test alternator. Their handheld tester read alternator fine, battery good but at 69% charge. Vehicle is also running about 2-300 RMP higher than normal.

My natural instinct is bad alternator (its my 2nd one and its a reman) but the really high voltage has thrown me curve. I expected under-volt not over.

Any ideas greatly appreciated!

 

Alternator is bad..

 

That's what I would say. Alternator can cause some strange symptoms. Also check your belt.

 

Likely the voltage regulator in the alternator is acting up. Assuming it has a lifetime warranty, I would just replace it again.

 

No way your battery read 14.6 off the shelf.

 

Maybe his Truck is powered by 24V

 

Under charging that should be about the max the battery sees from the alt. Your battery should read from 12.2-12.6 if it is good and charged.

Replace the alt and you will be fine.

 

Thanks for all the feedback guys! To idb2328 - I know!! 14.6 v is insane - but I assure you its a good quality digital voltmeter and I tested it siting in back of our mountaineer before install, then again at install before cranking to make sure to note the voltage for troubleshooting. 14.6 both time. Its an autozone duramax gold (was only thing in stock when last went dead, and got this replacement free under warranty). May be indicator of duramax quality, dunno.

Tore into it today and ran some dio tests - found straight voltage going thru the regulator. Tested point "F" on regulator to negative chassis ground on vehicle and got 14.2 volts.

Unfortunately now, its a Motorcraft alt and no warranty so Im stuck with taking chance and just replacing regulator or shelling out the bucks for all new alt (with lifetime warranty of course).

 

LMAO - LOVE the meter w0lvez - but i swear I tested the battery before install and after and got 14.6 volts......but...

got really curious about the voltage thing so dug out my better meter in the garage and behold 12.62 volts.

BTW ALL - I now got a handheld digital meter will sell for cheap.

 

AutoZone like to keep old batteries and just charge them. You probably got one right off the charger. zthat would explain the 14+ volts.