Weird Electrical Problem
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Joined: Aug 2004
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Weird Electrical Problem
Heres a new one I havent been able to find a topic on:
97 F150 4.6 engine 180000 miles. After driving a short time (about 15 min) I noticed the voltage on the guage begin to slowly drop. When it gets to about 8 volts the relays go crazy and the dasboard gauges all go to zero. This includes speedometer and tach. Engine coughs and sputters but does not go dead. The battery light flickers on and off in fairly quick fashion. Pull over, rev the engine, then the voltmeter jumps back to normal, everything comes back on line as if nothing happened. This cycle repeats about every 20 min or so.
I had changed the alternator about a year ago. Come to find out, the alternator was going bad. No hard failure during the voltage drop, no indication such as battery light that there was a true problem until the approx 8 volt range.
Switched out the alternator and everything appears back to normal. Boy do I like the lifetime warranties!! Hopefully the problem is permantly resolved.
Has anyone else seen this type of electrical problem? In the past, if my alternator has failed it is usually a hard failure.
97 F150 4.6 engine 180000 miles. After driving a short time (about 15 min) I noticed the voltage on the guage begin to slowly drop. When it gets to about 8 volts the relays go crazy and the dasboard gauges all go to zero. This includes speedometer and tach. Engine coughs and sputters but does not go dead. The battery light flickers on and off in fairly quick fashion. Pull over, rev the engine, then the voltmeter jumps back to normal, everything comes back on line as if nothing happened. This cycle repeats about every 20 min or so.
I had changed the alternator about a year ago. Come to find out, the alternator was going bad. No hard failure during the voltage drop, no indication such as battery light that there was a true problem until the approx 8 volt range.
Switched out the alternator and everything appears back to normal. Boy do I like the lifetime warranties!! Hopefully the problem is permantly resolved.
Has anyone else seen this type of electrical problem? In the past, if my alternator has failed it is usually a hard failure.
Senior User
Joined: Dec 2003
Posts: 212
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From: Spruce Pine, NC
Alternators have a couple of failure modes. especially the ones with integrated voltage regulators. your situation is one I have encountered before. Also, the battery can have an internal short that is intermttant - seems fine one minute, then dead the next. This type of short can also load an alternator to the point of not being able to supply the rest of the car with voltage. This can take out the alternator if not fixed quikly. Make sure the alternator is the chicken and not the egg. Could also have a faulty battery.
Posting Guru
Joined: Jan 2004
Posts: 1,254
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From: Murray
Might sound stupid or silly but...
Could be a loose belt too. If its running too loose around the alt. pulley it could be that its just not charging continuously. It drains the battery and then when you pull over and rev it for a while, while its not under load the belt will run tight enough to chrage it till you take off down the road again and put it back under load. Makes sense to me and I had it happen on another car of mine once. Now that you replaced it you coulda put the belt back on tight enough where it wont do it.
-Chris
Could be a loose belt too. If its running too loose around the alt. pulley it could be that its just not charging continuously. It drains the battery and then when you pull over and rev it for a while, while its not under load the belt will run tight enough to chrage it till you take off down the road again and put it back under load. Makes sense to me and I had it happen on another car of mine once. Now that you replaced it you coulda put the belt back on tight enough where it wont do it.
-Chris
Hotshot
Joined: Jul 2005
Posts: 11,931
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the truck is run by a computer. the electronics in the truck are based on seeing 11-14 volts supply. if you go less than that, then you will see gauges flutter, lights turn on and off, radio go crazy etc. i have seen this a couple times. if you take the battery loose while running the alternator may spike to 18-20 votls. thats not a pretty site either and can damage the electronics. you are o.k. to go now.
