Will an alternator act-up intermittently? I have a '95 F-150 4.9 and the amp meter always ran at just above mid point. The other day, it droped significantly and the battery began to discharge. I tested the output with a volt meter and it was only producing 12.5 volts. I removed it and took it to Autozone to be tested and of course it tested fine. Put it back in the truck and it was fine, for a few days. Now its back to producing about 12.5 volts. I'm prepared to buy a new one, but could this problem be anything else?

Thanks for the help.

 

Yes, if it is replaced buy a new one from NAPA, Ford, or a local rebuilder that uses quailty parts. Drive past Autozone, Pepboys and the like.

 

You may have a loose connection in your instrument cluster? See some of fhe recent threads about replacement clusters causing the charging system to stop working. It seems that the "AMP" bulb in the cluster, or the resistor that's connected in parallel with it in later models, must be passing current for the charging system to work.

 

Sound like a bad Battery ground Cable. Clean at the Battery, block and body. You may have to replace the Cable. High resistance makes the regulator think the battery is charged higher than it is. This can also be the Positive Cable.

Also a another possibly is that your alternator brushes are wore down, You cat try replacing them, they are only a couple of bucks, and change from the outside with only two screws.

 

my alt. gauage was dipp'n real lowwhen icame to a stop or had alot of draw on it(wipers,lights heater fan) had mine tested and it was fine, come to find out that since my iac wasn't work'n properly keep'n my rpm at the proper rate the alt. wasn't spinn'n as fast as it should

 

Thanks for the input.

I took the alternator out again this morning and the folks at Napa tested it and it worked OK. Put it back in the truck and you guessed it, no charging. Backed the truck out of the garage and the volt meter jumped back up. Verified it was putting out 14.5 volts. Turned on blower, lights, etc. to put a load on it and it quit charging. After about 10 minutes, it started charging again. Definitely an intermittent problem.

 

I have experienced the same problem, it does happen, not all things electronic pass or fail, they are often intermittant. If you are reading less than 13.5 volts at idle with the accessories off, you probably are experiencing an alternator failure. Where did that alternator come from exactly?
When you had the alt in your hand did the pulley spin very easily? It shouldn't have.
If your alternator has two plastic electrical connectors and an external fan under the pulley , I mean a fan that is visible outside the housing, then you should get a 3rd generation alternator, see fordfuelinjection.com there is an article about switching over. You could have a better alternator that works longer and is stronger.
I had alt problems for years with my 92 and 2 years ago I upgragded to a Third gen alternator with the internal fan and smaller belt pulley. It has terminal lugs for certain wires and does not cause fires in the harness as the 2nd generation alts do.

 

The alternator is a Motorcraft so I assume it is the original. I have 150K on the truck. The pulley turns very freely and makes no out of the ordinary noises. It has an internal fan.

I've read in the forum about error codes. Does my truck have them and if so, how do you get them?

 

http://fordfuelinjection.com/?p=13

This is the how-to for pulling codes with a ford EEC. The same site has a list of what the codes signify, as well as a plethora of other EFI information.

 

OK, 150,000 miles might be enuf for the alternator, that was a good run.

 

Yes, I tend to agree, but I've had it bench tested twice and it comes up OK. That is a concern if I'm going to drop +/- $150 on a new one. Going to call an automotive electrical shop next week and run it by them.

Thanks again for all the input.

 

I've got 215,500 on my original alternator!!!:P. Its just matter of time til it goes lol.

 

In my newest project truck i put a single wire powermaster, but i haven't got that many miles on it yet so we'll just have to see how that goes ? I've used an auto meter alt gauge on the last two, and wit the single wire alt set up, the needle stays on 14 volts no matter what i turn on.But like I said not many miles yet.(cross'n fingers, knock'n on wood)

 

I agree with Subford, you may have a ground or cable problem, it's intermittent and it's either working or it's not. It could be something else but I would check my cables and grounds first. Good luck.

 

you said you used a test meter and observed 12.5 VDC, at one time, so we are sure of at least one thing, there is a problem....the alternator was not charging the battery. If a test meter across the battery posts reads 12.5VDC any time the truck is at proper engine idle or above idle speed, there is a good size short, a heavy heavy current draw or problem with the alt.There should be approximately 13.5VDC on the battery terminals.
Most grounds or basic wire connections are usually bad or good, wires fail because of corrosion, stress, or loose terminals, but they are rarely intermittant, anotherwards, once a wire is corroded, or a ground screw is loose it will get worse and worse, not jump from good most of the time to bad one day a week.
I always suggest this: go for the easy cheap repairs first. In your case, that would be checking the wires to and from the battery and alternator. Clean the battery posts, inspect the battery wires for excessive green or whitish corrosion in and around the cable. Put a wrench on your ground lugs, loosen them up, clean them with isopropyl alcohol, and retighten.
Unplug the alternator and clean the connector pins with isopropyl alcohol or a basic can of "Electrical contact cleaner"
Check and Clean the lugs on the starter relay.

I like to use bearing grease or even vaseline on all terminals around the battery. The grease keeps an airtight seal around the terminal, and minimizes that nasty electro-chemical corrosion that gets all over the battery area.
Baking soda and water are a good cleaner for the battery also, the alkalinity of the baking soda neutralizes acids and stops corrosion in its tracks. Apply baking soda and water mixture to corroded area, let it sit for a few minutes , then rinse it off.