I just had the factory alt go out on a 2005 Supercab F 150 XLT 4.6 L motor. After I replaced it with a reman alt I checked the voltage as the truck was running at the battery and got 13.9 volts with a warm engine and 600 approx rpms. I also got a brand new motor craft 850 c/a battery so the batt is good..
Couple of questions:
1 Is this enough volts for my setup??

2. After I replaced it , the red battery light stays off now and the gauge reads perfect like it should. But I notice that when I am coming to a stop the idle drops to 400- 450 rpms and then goes back up to 650 -700. Also when the ac comp kicks on it does the same. Did I get a faulty alt???

I know the computer has to reset itself but is this normal?

Thanks for the advice

Keith

 

imo i think thats a little low, 14 is about where you wanna be... but let the experts come in and back me up.

 

Right, 14.6 I believe or close to it. It's definitely not 13.9 running. That's a bad one. Your best bet with alternators is to get the real deal online. Getting a bad rebuild is far to common.

 

Thanks Guys. i had to buy this because I was out of state and this was all they had at the auto store I ended up at. The thing got me back to texas though --LOL-- But now I just sent VISION OE reman a message and told them they have a faulty reman and asked them what they can do for me since it is under waranty . Where would you guys suggest for me to get a new motor craft alternator besides going to the FoMoCo dealer? also who do you order these kinds of parts from that are dependable ?

Keith

 

tasca or try rockauto

 

Thanks a bunch

 

Starting in 2004, the PCM controls the voltage to the alternator via PWM signal. If the alternator is off by % of requested voltage the PCM is asking for, then a DTC will trip. PCM voltage control range is between 13.3 and 14.7v. The voltage is set solely based on a calculated value of the battery temperature. If the PCM believes the battery temp is high, it will drop the voltage and vice versa. Anything above 12.7v and will charge your battery.

That doesn't explain the dips in the idles but thought I would explain how 2004+ MY trucks votlage control works.

 

Thanks Storm. I called the people at Vision bbb industries who remanufactured the alternator that I bought and he explained the exact same thing to me yesterday evening. So I got to thinking that when I tested the voltage it was on a NOT fully charged battery so last night when I got home i checked it again and I am getting 14.4 volts at the battery while running at idle. Also I noticed the idle problem has gone away especially with the A/C on. I assume that when I disconnected the battery it reset the computer and has been learning my driving habits again. I have only ran the truck for a total of 4 hours since I changed the alternator and 3 of them were on the highway. The truck runs like a top now with no idle problem. Also it seems to have more pep and it starts with just a bump of the starter. I think I am ok but will keep an eye on it for sure Thanks for the input and advice.

 

13.8 volts is standard they vary slightly. This is not your issue IMO

 

https://www.f150online.com/forums/v8...uck-stall.html


Check out this post
I had same idle issues and this helped me out.

 

Not really. I have owned several new Ford F-150's as well as several other brands. ALL, have run at about 14.2-14.4 with the exception of the GM's (been a long time since any of them!) which ran less (about 13.8 to 14.0). I generally test my V. at about 14-1500 RPM.

 

Thanks HeavyD I will look at that IAC this weekend and clean it as well , Thanks for the info I am getting good voltage at the battery now 14.4 and some times 14.5 volts also the idle is a lot better but I will do the cleaning and want it to idle way better --LOL-- Thanks again

 

Huh.. Interesting

 

PlanoKeith150 you don't have an IAC on your truck! It's a 2005 and the F150 uses the computer to manage the idle with the "gas by wire" starting with the new models in 2004. You can clean your MAF and T Body for starts, but good luck finding your IAC!

 

Thats fine but he's talking about a rebuilt alternator. I think we're cutting hairs here...13.9 and 14.5 makes no difference in the operation of the vehicle and minimal difference in the charging system. Lets remember The vehicle's electrical components are 12 volt. Thats what they need, give or take.