12.6 is a reasonable voltage for a battery, but voltage won't tell you enough info to rule out the batteries. You need a hydrometer and a load tester to really know for sure. ( Picture a little square 9 volt battery, has 9 volts but would never have enough capacity or amperage to xtart a truck, even if it was a 9 volt starter motor).
If your batteries are weak, your system voltage will drop down and maybe the IDM is not getting enough power to the injectors.
When you did have the batteries checked they should have been load tested. I f they checked good under a load test, they're probably OK. You may want to give the batt. cables a good checking over also.
If the tach is working erratically you may want to check the CPS again. I know of a couple of people who got a month or less out of a new one.
When the truck does first start, let it run just a few seconds then shut it off. Working cylinders will feel warm on the ex. manifold, dead cylinders will not.
The wiring harness under the valve cover is also a possible culprit.
Keep us posted-

 

My exact thoughts I was just gunna post this.

Diesel Rod

 

bump
bump bump

 

sounds possibly like a vc harness problem if your only running on 4 cylinders. pull the plugs at the vc's. do you see anything burnt? how about the vc gasket look ok? if so then pull vc's and check it out. possible you have burnt uvc harnessses. if not those then you may have a bad idm.

 

its at the mechanics shop now andspoke with him. he said the wire harness in side the valve cover is fried. and the plug on the driver is bad also. asked me if the truck had a miss at all. told him that every once in a while she would skip a beat but nothing to serious. he also toldme this is a fairly common problem. looking at around 400 to rapair. and a fewmorebucks for adding glow plugs and a compression test. thought i would let everyone know. if you have a problem like thischeck out the injector harness. jack k

 

another guy had a problem like yours, you may want to check it out. it was also cold when his problems started. the cold weather may affected you wiring too.

Ford Truck Enthusiasts Forums > Diesel > 1994.5 - 1997 7.3L Power Stroke Diesel
Starts fine runs rough


Here is an update on our 95 Ford 250 4x4 deisel. With 336,000 miles, (385,000 was incorrect) this truck has never failed to start for me. Two weeks ago, on a very cold morning, one mile from the house, the truck cut way back and ran rough but never died. I shut it off and restarted. It started fine and ran for about 15 seconds and then cut back again.

I pulled the VC on the drivers side and found one of the pins on the front wire harness was burnt. Replaced both harnesses and replaced VC. Started up and ran fine for about 45 seconds and then same as before.

I then pulled the VC on the passengers side and found a major melt-down. The front wire harness was mostly burnt (See pics. Have you ever seen it so clean under the cover with 336K? http://www.imageplusinc.com/pages/truckpics.htm ) I replaced both wire harnesses and the VC. Startup was fine and she is running smooth.

Thanks Mike From Shiloh. You were right on.

Thanks to all for the suggestions. Hope this might help someone else.