My 1994 f-150 is having some problems with the motor that are out of my leagues. I first thought the problem to be the alternator but am definetly having second thoughts.

Last week when trying to leave work my poor truck would not start. We later determined that the problem was the battery which still had juice but was the original battery from 94'. Since replacing the battery i'm now having problems when the truck is in park, running at idle. She starts fine but then the voltage gauge will drop and rise drastically. You can hear the engine fluctuating with the voltage gauge. Sometimes it will go away after a few minutes, but lately it will just die on the spot after a few drops in the rpm's. The funny thing is that when you put it in drive while the voltage gauge is at the top end the problem stops and the truck runs fine. please let me know if you've ever encountered similar problems.

 

Actually, I did have a problem almost exactly like that. Turns out, the dead cell in my bad battery caused the alternator to overcharge as compensation for the bad cell.

The overworked alternator developed it's own problems because the connections inside the casing on the back side of the alternator had overheated and melted the solder holding them together. No load situations, like idling, didn't draw enough current to arc the voltage in the bad connection, so it stumbled and died alot. Under load, it pulled more voltage, allowing it to arc across that bad connection, so it ran pretty good.

Meanwhile, the computer is working overtime trying to compensate and correct for all the amp and voltage inconsistencies, strangely enough... it didn't pull any computer codes, just a battery/amp light and check engine light on the dash

So I had to go back to old fashioned troubleshooting to determine the problem. Since I had just replaced the battery, I was pretty sure that wasn't my problem and I had no problem starting the truck so I eliminated problems with the starter solenoid. Next I spent 10 bucks and replaced the voltage regulator... no difference. I checked the coil output with a voltmeter and it was up to specs. Only one thing left (besides the computer). So I pulled the alternator.

I tend to be a do- it- yourselfer when it comes to auto repair and curiousity got the best of me. I HAD to crack it open and figure it out. Turns out, all I had to do was resolder the two burned connections. I replaced the brushes (since I had it open) and put it back in. Been running great every since.

Sometimes, patience and a return to good old basic mechanics can mean all the difference.

 

This is exaclty what i was looking for. I had the alternator tested while i had the bad battery still in. The mechanic told me that with the battery as it was the alternator was over compensating. The alternator was reading good though which is why i had suspected something other than the alternator, but from what you've described i think i know what i have to do. thanks again.

 

Let me know for sure if that's what the problem was...