1994 f150 5.0 charging problem

when truck is running and you stop the voltage drops down very low. start up again and it picks up again to normal. when you first start it, it's ok but when it warms up it drops when you stop. i have
replaced cables, cleaned ground, tested voltage at battery ok when you speed it up.what else should i check? the alternator looks new, i think it's beck arnely or something like that. otherwise the truck runs fine.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Get a multi meter and find out how low is low.
--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Backyard Mechanic wrote:

I don't know how low it is dropped, but both ford trucks i had did this... now we're talking a drop of 2 volts maybe, 3 tops.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Picasso wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
str-8 wrote:

Without a voltmeter, it's just a guess. Normal system voltage is pretty "tight", in the 13.5 to 14.5 volt range, depending on heat and state of battery charge. It sound like your warm idle is too low, causing the alternator to not be charging at low rpm.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Picasso wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.