So I get the altenator done. I ride around for about an hour. Wash off the motor and come home and plug in the block heater. I go to leave and it starts right up. I go less than a half a mile and it just quits. Now it will crank but it wont fire.Any clues out there as to what might be wrong?

What year?

04 6.0 powerstroke.

I have checked all my fuses. they are good. But I do have one battery that is down. Could that be a problem?

Sorry, can't help. My little bit of knowledge is all 7.3. If its cranking I don't see how the battery is the issue. Good place to start though.

Try thedieselstop.com. Slow forum, but lots of good Ford info.

Cam sensor.

Look at your tach when you crank it. If the tach is not moving, it is the cam sensor.

The above has happened to me twice. Another easy fix that has happened to me your will want to check next. Does the wait to start light come on. If not, you may have a fuse blown from your fuel bowl heater. Not sure if it does that for all years, but check the fuse for your fuel bowl heater. If blown, unplug the heater (use google to find it) and replace the fuse.

And I have also replaced my fuel injector relay twice now. This will cause this. It is actually called something else, but can't remember it at the moment. Looks just like your starter relay. Easy to replace if it. If your truck was getting hard to start sometimes, it could indicate this was on it's way to fail.

All three of the above and a spare starter relay with the wrenches to replace them should be carried in your 7.3L truck IMHO. You will have one or more of them fail eventually.

Not uncommon for the fuel injector harness under your valve cover to fry. I had one fry in the middle of nowhere of a CO National Forest. This will also allow you to crank your truck, but no starty. Easy to change, but hard to find if your in the middle of nowhere. Look at the wires around your connectors along the valve covers.

Mine is an older model, so some things might be slightly different, but it might give you some direction.

Yes absolutely, fully charge both batteries then load test them.
If one is bad replace both.
It's best to spend $100 on a battery to prevent spending $800 on a Fuel Injection Control Module.
Low voltage or shorts caused by bad / weak batteries or a faulty charging system will ruin the FICM in a big hurry.

Recheck all fuses in cab and under hood. Best to do it with a multimeter, every now and then you'll run across a fuse that appears good to the eye but isn't.

If it still won't start with 2 fully charged and tested batteries you'll need a scan tool like a dealer or good independent shop uses for further diagnosis. The code readers used at parts stores will not read advanced DTC's or perform the diagnostic tests needed to prevent throwing money and unnecessary parts at it.

If it does start get the charging system checked, I've seen a several rebuilt and a few new alternators that don't supply the proper voltage and amperage.

The 6.0 and 7.3 are quite a bit different.

Could be low voltage from the FICM or hi psi oil system leak.

6.0 & 6.4 powerstrokes are junk I have personally owned both and unfortunately still own 1 of each 05 f350 & 08 f450 as work trucks for a crew. I have moved back to the Duramax until the new 6.7 has proved itself!!!!! sorry for your luck hope it turns around!

Had a lot of friends buy the 6.0 and 6.4's and they have had a lot of trouble.There is a lawyer in Dallas that put a ad in our newspaper (Fayette County Record) and he is going after ford with individual lawsuits. You might check it out. I will pm his ad or name if you all need it.