Voltage issue, believe it is something with my blower motor

[fallenauthority]

Ok so when I bought my 96 4.0 OHV explorer a couple years ago I noticed that during the winter if I had the heat on full blast with the headlights on and I came to a stoplight the voltage would drop WAAAAY low, like 1/4 of the guage. If I let it stay this low without giving it a little gas to perk up the voltage the truck would throw lean on bank 1 & 2 codes after a couple minutes.
So I adapted to turning the blower down to like 2 at stoplights.
Fast forward to this year same issue, except the voltage drop seemed worse. So I decided to buy a used alt off a member here, got the alt, noticed it had a much larger pulley on it than the one I took off so I imagine that the alt I bought is the 130amp as compared to what I assume was a 95amp that I took off.
Put the alt on, idles with voltage a little higher than it used to so I figure I fixed it, I drive around a bit let the truck warm up without anything but my stereo on, I even turn the radio up a bit, I have subs that used to make the gauge drop with hits of the bass, but now the gauge doesnt drop with the bass hits. So now I figure it is time for the REAL test, turn the heat on full blast, shocker, voltage still drops with heat on full while in drive stopped at a light with the headlights on. It doesnt get near as low as it used to but the headlights and dash lights still dim.

I figure since the only thing that can seem to draw the voltage down so much is the blower motor that maybe after 14 years and 212k miles maybe the blower motor is just wearing out and drawing a ton of current, am I way off base here? Sorry for the long read but I know that information is key to diagnosis so I didnt want to leave anything out.

 

[RockyMtnHigh]

Ok so when I bought my 96 4.0 OHV explorer a couple years ago I noticed that during the winter if I had the heat on full blast with the headlights on and I came to a stoplight the voltage would drop WAAAAY low, like 1/4 of the guage. If I let it stay this low without giving it a little gas to perk up the voltage the truck would throw lean on bank 1 & 2 codes after a couple minutes.
So I adapted to turning the blower down to like 2 at stoplights.
Fast forward to this year same issue, except the voltage drop seemed worse. So I decided to buy a used alt off a member here, got the alt, noticed it had a much larger pulley on it than the one I took off so I imagine that the alt I bought is the 130amp as compared to what I assume was a 95amp that I took off.
Put the alt on, idles with voltage a little higher than it used to so I figure I fixed it, I drive around a bit let the truck warm up without anything but my stereo on, I even turn the radio up a bit, I have subs that used to make the gauge drop with hits of the bass, but now the gauge doesnt drop with the bass hits. So now I figure it is time for the REAL test, turn the heat on full blast, shocker, voltage still drops with heat on full while in drive stopped at a light with the headlights on. It doesnt get near as low as it used to but the headlights and dash lights still dim.

I figure since the only thing that can seem to draw the voltage down so much is the blower motor that maybe after 14 years and 212k miles maybe the blower motor is just wearing out and drawing a ton of current, am I way off base here? Sorry for the long read but I know that information is key to diagnosis so I didnt want to leave anything out.

My 98 XLT 4.0 SOHC was doing the same thing. I was going to check everything out but last spring it suddenly "fixed" itself one cold day. It lasted up until about a month ago and now it is doing the same thing again: when I stop, the voltage guage drops down low (still in the normal range though), the headlights dim and the blower motor will slow, if on. The truck always starts fine and the battery always has lots of cranking power, even in extreme cold.

I am suspicious that mine is either a bad ground, rotten cable or the battery itself. I have also thought that it could be the alternator, but as your experience proved, it is my last suspicion.

Has anyone else had this problem and solved it?

 

[BrianDye]

I think it is a little normal being stopped, the alternators not at its cranking capacity so its barely "putting out" so to speak : but it shouldnt cause your truck to throw codes. Id say check your terminals, AND wires. Our battery cables are notorious for being corroded on the inside even when the ends look clean. Ive read thread after thread about electrical problems solved with new cables.

You could also try doing the "big three" mod, which is basically upping your cables to a thicker, higher quality cable. (Do a search if interested)

 

[fallenauthority]

Yea I was thinking I will try the big 3, I already had that in mind, wouldnt hurt especially since I have a stereo system and it would get rid of the old probably half rotten factory junk. I will keep this thread updated as I go.
There HAS to be some way to keep this drop from happening other than buying an alt from alternatorparts.com or whatever, saw one guy on here had one and it only lasted 1.5 years, Im not into the replace the same part every couple years thing.

 

[BrianDye]

You could install a smaller pulley on your alternator...

 

[fallenauthority]

Well I have the smaller pulley that is on the alternator that I took off of the truck. So I guess I could swap the larger pulley out for the smaller one. Will there be any adverse effects? I dont want to go frying anything.

 

[BrianDye]

The purpose of the smaller pulleys (I believe the term is "underdrive" pulley) is that at a lower RPM, such as idle, it will be spinning the alternator faster, causing it to charge faster etc etc. Pretty much self explanitory. I have heard a few people say that it will shorten the life of the alt, since its spinning more, but I doubt it will have much effect.

 

[fallenauthority]

The purpose of the smaller pulleys (I believe the term is "underdrive" pulley) is that at a lower RPM, such as idle, it will be spinning the alternator faster, causing it to charge faster etc etc. Pretty much self explanitory. I have heard a few people say that it will shorten the life of the alt, since its spinning more, but I doubt it will have much effect.

A smaller pulley on the alt would be overdrive
But after thinking about it, the smaller pulley wont hurt due to the fact the alternator output is regulated internally anyway, so it should work with no issues, I will give it a shot, maybe tomorrow.

 

[fallenauthority]

Swapped pulleys today, smaller pulley on the 130amp works like a charm