Judging from previous threads, it seems pretty certain that I need a new alternator, but I want to be more sure. My battery light is coming on whenever my foot is not on the gas. The battery is brand new, so it is still at the proper level, for now I imagine. New alternator? Any suggestions on a fair price for one? 1997 4x4 4.6, 160k miles

 

I would recommend removing the alternator, and going to your local FLAPS (Friendly Local Auto Parts Store) and they can test the alternator for free.

Alternators probably wont cost too much (under 200 bucks). 160K is pretty good for the OE alternator.

Good luck!

 

With the car running disconnect the hot (+) form the battery, if the is a noticible drop on your idle speed, it's time to take the alternator into an auto store to get it check. if there is no drop on your idle, voltage regulator might be at faul, I dont know if they are now integrated in the alternator or not, I know that my Bronco isnot. if you have an autozone by your house they have an alternator/ battery tester that you can use but the disconect the positive has worked very efficiently for me.

 

thanks guys. I will likely replace the alternator anyway, regardless, just to be safe. 160k is a lot for the OE, so even if it's ok, which I doubt, I'll fix it anyhow. I think the voltage regulator is intergrated in the alt, anyone?

 

yep, internal regulator.

 

[QUOTE=Dre82s]With the car running disconnect the hot (+) form the batteryQUOTE]




YOU NEVER do that! That is a really good way to fry sensors and the ECM.

 

Never, ever do this.


The potential for significant electronics failure is there.

 

Yes... DISREGARD Dre92s' post... it is very dangerous advice on ANY vehicle that has computers.

Yes in the past it was a somewhat valid test when the amount of electronics in a vehicle were minimal. Simply put, if the alternator was not charging, then engine would die when you disconnected the battery. Even back then though, it was a "backyard" way of doing things.. a voltmeter will draw the same exact conclusions with no danger.

Not only does the battery provide power to start the vehicle, but it also serves as an "electrical reservoir". Think of it this way... your coolant reservoir provides extra coolant during times when you need it (cold starts) but also extra capacity for when your cooling system heats up, pressurizes, and needs to expand... the extra expansion goes into the tank instead of on the ground.

Well the battery is kind of the same thing.. without it, all electrical spikes and surges in the system are no longer absorbed by the battery.. they can DIRECTLY hit the modules and computers... and chance of fry-age is very high. And guess what? The more complex these computer systems get, the more susceptible they become.

Regasset, get a volt meter and check the basics.. first make sure the belt is tight.. then start it up and check voltage on the battery. At idle (with nothing turned on) you should get a good 13.5-14.5 volts. If you turn all the accessories on at this point, you should still be reading at least 12.8 volts or so.

If you are getting lower numbers, then yes it's most likely the alternator, but to be 100% sure check the main power wire at the back of the alternator.. it should have battery voltage at all times. Also check your battery cables.. make sure they aren't all corroded up and all that as high resistance can really screw up an electrical system.

good luck

 

I'd say that it's very possible that you need a new alternator-The slip rings on the alternator are likely worn out along with the brushes from the regulator. I've purchased 3 alternators from this seller on eBay:
http://cgi.ebay.com/ebaymotors/New-MotorCraft-130-Amp-Alternator-Ford-Truck-E-350-Van_W0QQcmdZViewItemQQcategoryZ33573QQihZ015QQitem Z250119651373QQrdZ1

They're a direct replacement for the F150 alternators on 4.6L,5.4L,and 6.8L engines.They're takeoff pieces for new RV conversions and are literally "open box" new in condition.
JL

 

i have heard that before of the battery cable, but has there actually been studies done ? i might be wrong but if your alternater is working properly you shouldnt see any spike. that is purpose of the alternater. the battery is just there to provide starting power and nothing else.

 

That is absolutely wrong. The alternator's purpose is to recharge the battery after starting, and to supply current to power your electrical accessories. The alternator does NOT have a high inrush reserve capacity-that's the battery's job-to supply an instantaneous inrush reserve for larger loads,and to act as a "filter" to the electrical system to soften large spikes of current draw on the electrical/charging system.
JL

 

Thanks for all the replies, good and bad. All in all, cost me $95 for the reman alternator on eBay and $75 for a local mechanic from craigslist to install while I was at work.