Electrical system does not charge above 70MPH

Advertise with us
shop deals on amazon
Shop deals on ebay
Ford SportTrac Forum

Help Support Ford SportTrac Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
O

One TracMind

Member
Joined
Dec 18, 2005
Messages
21
Reaction score
0
Location
, NC
This application is actually for a friends Ford Ranger but we have found solutions for both Ranger and Sport Trac's problems through this forum.



As the title suggests the trucks electrical system does not charge above 70MPH. He can visually see the in dash amp gauge gradually fall down when traveling above 70 as well as gradually diming lights. The warning (idiot) light never comes on regardless of speed but in does check OK when vehicle is first started.



My first inclination was bad diode in the alternator but yet no light. Then I thought battery path but when the problem was further diagnosed to being speed related that path was iffy.



Anybody care to throw an idea?

 
I agree with Les. I don't think it's a diode, it sounds like the belt, or something else RPM-related. Focus more on engine RPM than vehicle MPH. Check the voltage with a multimeter while the engine is idling, then while the vehicle is in Park and the E-brake is engaged, or better yet, up on four jack stands have someone rev the engine up and down the RPM range and see what it does. Then, check it while holding the RPM's up around what they would be at 70mph.



Also, take it to Autozone, Advance Auto, or whatever auto parts store is in your area. Most of them run an electrical system check for free. This might help you diagnose the problem.
 
Belt and or Belt Tensioner is my guess...



And even if we are wrong, I will bet the belt is WAY past due on replacement.



I think if you change the belt you will solve the charging issue, have a new belt, and not have a high speed power steering issue which is common with the Trac once the belt is worn...
 
Do you know the age or millage? A agree with everyone else try the belt second, but go to Autozone or one of those stores and have them run a test for free.
 
I agree of the above. The belt is probably due for replacement and is slipping at high RPM. While you are replacing the belt, it won't hurt to remove the alternator and have AZ check it. It may have a regulator problem.
 
Worn brushes/slipring in the alternator. Fords are notorious. Best fix is a brand new alternator. Rebuilt from Autozone is something like $150. Good luck.
 
Worn brushes/slipring in the alternator. Fords are notorious.
Click to expand...



With over 50 Fords in my family, this "notorious" issue is something I have never heard of.



Please elaborate.





Tom
 
Caymen, I actually just saw this last week on a '99 Mercury <s>Mistake</s> Mystique. The alternator would charge just fine until it got some speed on it, then the voltage would drop.
 
We've seen it on several Tauruses and my '03 Trac had the same problem. Charge light comes on at high RPMs. Guy at the rebuilder place said that the brushes/springs get weak and they don't make good contact and then the charging output drops off.



Said that by the time you put in the labor to tear it down, you might as well just throw a rebuilt alternator on it with new bearings, etc.
 
We've seen it on several Tauruses and my '03 Trac had the same problem. Charge light comes on at high RPMs. Guy at the rebuilder place said that the brushes/springs get weak and they don't make good contact and then the charging output drops off.



Said that by the time you put in the labor to tear it down, you might as well just throw a rebuilt alternator on it with new bearings, etc.
 
With over 50 Fords in my family, this "notorious" issue is something I have never heard of.
Click to expand...



For the older Fords I agree, this was not a problem. But the later models, from the 90s, can have brush issues as Dingo pointed out since the brush spring may have been over-heated and doesn't ride well on the rotor. Also, at least when the current generation of Ford alternators was introduced, the regulator and brush-holder from the old alternator was used on the new alternator at the dealer, however,I don't know if this is still true.
 

Latest posts

Top