I have a 95 f250 and have been having a weak start. I had my alternator tested along with my batteries. The batteries checked out ok but the alternator showed that the voltage regulator was bad. I rebuilt my alternator with all new regulator and brushes. And still the same problem. Almost seems as though the batteries aren't charged all the way but when I put a meter on them I get 12.5 to 13 volts. Another weird thing in my battery gauge shows low until I get going down the road then it jumps up to normal position and everything g is good. Is it just time for a new alternator or what. I can't figure it out. Thanks for any info.

 

Was the batteries load tested together or did you disconnect the from each other ?

The volt gauge jumping up is normal. When it goes up that is when your glow plugs are turning off

 

Have you made sure al your cables are in god shape and grounded properly? They can be a mess if you live in a place with lots of corrosion.

 

I tested the batteries separate from one another. And when I say the battery gauge jumps up I mean it reads like 9 volts after it starts then jumps up to the normal position after it has been running for a few minutes.

 

That's what Mike said, the glow plugs will run up to two minutes drawing lots of juice. When the engine is warm and you start it, you shouldn't see that 'jump'.

 

So one of the batteries was disconnected?

That's not a battery gauge. That's measuring SYSTEM voltage. And yes, while the glow plugs are running (up to aprx. two minutes), the load of the GPs will pull the voltage down. Usu. it's more like 11V rather than 9. But the fact that it's lower for the first minute or two is totally normal. When the GPs cycle off, system voltage should be about 14V.

 

if that's normal for the gauge then I'm not too worried about its just that it just started doing it. It hasn't been like this up until the last couple weeks. And with the alternator test showing the voltage regulator was bad I didn't know if I had an issue with the system somewhere. Just don't want to be stranded somewhere.

 

So here's what I was talking g about with my voltage gauge acting up. Forgive the wife and kids talking. Lol. It's low to begin with and will sometimes act like it will die then it jumps all the way to where it normally runs and all is good. Is this really normal?

http://youtu.be/lQN29WTRSzw

 

It does seem to crank slow. Whether that is battery cable connections, batteries,or starter I couldn't say, but it looks like it's charging properly. The glow plug system uses a lot of power and you can see when the glow plugs turn off at 21 seconds into the video. Before that as you raised the idle the alternator is able to produce more power and keep up to the glow plugs better.

 

^^^^^ +1; once again, voltmeter action is totally normal, reflecting GP cycle. But it does drop awful low during cranking (at work, so I couldn't play the sound on the video). Tells me either the batteries are weak, or the starter is drawing a LOT of power. You really need to LOAD test the batteries, and once again, make sure they're isolated for the test. Just reading voltage with no load doesn't tell you much.