M11 cummins issues

I just purchased a 98 international with a 400hp M11 that needs to be nursed back to good health. I've been to 3 different shops but neither could get a signal from either data port (under dash or on the engine itself) to try and pull up any codes to troubleshoot the problem. The truck idles fine but has a skip and puffs white smoke when accelerated. Also only one light comes on in the dash which I think is the engine stop light but I'm not positive. I've checked the external wiring harness with the engine running as best I could to see if there were any change in engine tune and I did find one wire that was maybe grounding out on the frame but that didn't seem to be the problem. Only other thing I can think to do would be to take the ECM off and go have it table tested to see if it will respond off the truck. Any helpful suggestions with this would be greatly appreciated.

 

Yes I figured the air fuel ratio is off too but I'm thinking its in relation to whatever my electrical problem is. The previous owner told me it needs a wiring harness but he's just guessing I want to be sure before I go out and spend $600+.

 

If I have to have one put on its going to cummins! I just want to exhaust all my options first.

 

6-8 hrs?? Wow! At $136/hr that can get expensive!!

 

Ok, well before I take the ECM can you think of anything else to check?