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Alternator & Battery Light

This is my 1997 Escort LX; 2.0L SPI engine. The car itself, but not the engine & transmission just flipped 290K today.

Two days ago my alternator went belly up. This was confirmed by my shop & the alternator was replaced. Note for later that my battery light never came on. (The death appeared to me to be quite sudden).

Everything was fine up until today when my battery light came on as I pulled into my driveway. I will bring it back to the shop - but I don't want to bring it back & have them tell me I need new cables or something for $[too much]. So I'm just trying to sort things out.

My battery is all of a few months old (the alternator didn't show bad based on auto parts store tests when I replaced it). The connections are very clean & very tight. The belt & tensioner are good. The alternator pulley is smooth & quiet.

So here's the part that has me confused. When I put a meter on it with the car running hot at idle with everything off it shows about 14.4V at the alternator terminal. At the battery its about 14.25V. If I turn stuff on the voltage fluctuates some. The only thing that really takes it down under 14V is the cooling fan. When the cooling fan comes on it briefly drops down to about 13V but then bounces back up (with the fan still running).

I put my son in the car to rev it & watch the tach. With a bit over 14V on the meter at idle the battery light would be on. He'd rev to just under 2K rpm & the voltage would climb slightly & the light would turn off. There was a "magic" spot at about 1900 rpm where the light would trigger on or off. Yet the voltage always remained in the range of about 14.1-14.5V. There are times when the battery light will remain off at idle, but this seems to have nothing to do with the voltage readings.

I connected my laptop-based scantool and watched the input voltage as read by the scantool & that just confirmed everything I found with the meter in terms of the voltage & fluctuation.

So....I'm not actually sure if the voltage output is supposed to fluctuate as much as it does - but in most respects I'm looking at voltage measurements that don't suggest a problem, yet I have my battery light coming on. Can anyone help me with what is going on?

Thanks.



Comments

  • One bump.

    That post was long - the short story is that by meter or scantool, measured at battery or alternator, my alternator seems to produce between about 14.1 - 14.5V, even with a load - yet my battery light is coming on.

    The radiator fan does give the system quite a shot & will briefly drag the voltage down to about 13V. It then recovers.

    The car was too hot to work on last night. Today I'm looking at over 100F ambient so I'm not going to mess with it until this evening.

    - I am suspicious of the load my cooling fan puts on it & suspect it may be drawing too much current.
    - I will clean all of my grounds.
    - I will pull, check & clean the alternator connections, though this isn't easy due to location.

    - Just wondering if what is going on points to anything in particular from those with more experience than I.
  • Be sure you check all the ground wires going to the grounding termial (black box) on the negative battery cable to be sure they are all clean and connected.
  • I am confused- You say your alternator died suddenly and it was confirmed by your shop but you don't say why you and your shop concluded your alternator was bad. You then tell us the bad alternator tested good at the auto parts store and relate in detail what your voltage reading are with your new alternator but don't tell us what they were with the old one on the car. With the information given I have no reason to think that either one of you alternators were bad.
    With a 14 tear old car that has had the engine and transmission changed i would suspect a crushed wire or bad ground someplace. With one person reading the voltmeter , have another person push and pull on all the wiring harnesses.
  • @oldtimer 11 There's nothing to be confused about. A couple of month ago I had to replace the battery. At that time - the old alternator was load tested at the auto parts store where I bought the battery. At that time the old alternator "passed" whatever load test their machine does on it. I bought a battery & went on my way. Its not part of this story. Its only backdrop info to anticipate questions about the battery & such.

    To describe why I suspected a dead alternator is a longer story than what I initially wrote. Suffice it to say that whatever the alternator was producing wasn't enough to run the car or keep any kind of charge on the battery. I was 15 miles from home without a meter in a dead car. I didn't ask the shop for the specifics of how they checked things out. It is a fully equipped shop and a simple matter. I've been using the shop for a long time.

    Anyway, thanks FordMan & oldtimer for the ideas. I'm hunting.
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