i have 2000 excursion 7.3 turbo. having trouble starting. have changed crank sensor . 2 new batteries , new alternater, changede oil and filter , fuel filter , tried checking all my connections with wiring harness" sometimes will crank over and sound like it should start but wont, redue the key andthe warming up part and she'll start . other times it turns over very slow, but if you do the key process twice it will start . the starter was my last replacement after changing it wouldnt start, i did check and push on a couple wires to make sure harnesses and such were tight. after playing aroud with it for a while it will sometimes start , ive had no codes come up as problems and 2 mechanics look at it and no one can find anything wrong , also ive been thru 3 alternaters , yet i keep getting told nothing will burn out the alternater ,some have lasted 3 weeks (shortest life) some a little longer, i had a 6 position bully dog on it but is off right now . any help?

 

Sounds like your glow plugs or even your GPCM or Glow Plug Control Module. Mine did the same thing just not as bad; it would crank and fire, but had to work a little more to start, but I've since replaced the gpcm and it hasn't done it since.

The gpcm is on the passenger side of the engine, it's a silver box with a black and green connector going into it. If it does throw a code, it'll seem as if an entire bank of glow plugs went out, classic symptoms of a gpcm failure.

 

I'm thinking bad ground, Hmmm

 

I also went through almost the same thing on our 2000 x with 7.3 and about 165'000 on it.
First the cps went out about a year ago so i replaced it and it started just ok after replacing it but not like it did before it went out.
Then it would seem to stumble when it started, seemed like one cyclinder was missing but only when it first started to run and would smoke alittle when it would start but would clear up pretty fast. My cousin works out of his garage as a mechanic and has a scan tool so we hooked it up and it said that the number 6 glow plug was not working so i replaced the 2,4,6,8 glow plugs and it didn't fix it. Then checked all the wiring to that side of the block and everything checked out ok. So i just drive it.
Then this late winter early spring it became harder and harder to start and you could glow it a 2 or 3 times and hold the starter engaged then it would start.The weather warmed up and it was 45 degress out and it wouldn't fire at all maybe one hole but would not stay running. this time I looked at the wiring harness going into the heads(both heads this time) that feed the glow plgs and injectors and found corrosion on the 1,3,5,7 side (passanger side) so i replaced both valve cover gaskets and under the valve cover wiring harness and the exturnel pigtail that plugs in to the outside of the valve cover gasket. Still had the stumble but it started like it did after i replaced the cps.
Got to looking online for the glow plug control module and saw that our 05 Excurion (6.0L) uses the same one so i switched them one morring and it started like it did when i bought it new. The valve cover work was not a waste but the 4 glow plugs are!
So i guess i would look at the wiring harness first, look where it goes into the head and also where it plugs into the gpcm, i have heard of those plugs going bad also. If you know someone with a 6.0 that you could use the gpcm it only takes about 5 minites to try. Let us know what you find and good luck!

 

Yea sounds like a glow plug related issue like Toredor said. When you go to start it check and see if you're getting power to the glow plugs, also check them while you're at it ohm them out with a multimeter. You don't say how many miles are on the truck if they've never been replaces probably wouldn't hurt. On the alternator issue .... where are you getting them from? If it's Advanced or Autozone those are junk anyway. Check all cables, grounds, connections, ect....