You'll have to forgive me for probably posting something twice...
First time posting...

Just finished a 2000 PI Head and intake swap on a 99 F-350.
Heads were surfaced, valve job, and helicoils installed. Also custom tune
Ran great for 5 days then developed a miss. Melted Motorcraft Platnium plugs.
Installed NGK TR6 plugs and pulled and reinstalled tune with 4% more fuel and -2 timing. Ran good for one day, now miss has returned at low RPM and under down hill load with zero throttle. Miss isnt present at higher RPM (over 1500-1800).

Driving me crazy, so I joined hoping for some help...
Any suggestion would be appreciated

 

I hate to say it but helicoils are about the worst insert you can get and most likely wont hold up, There was another post not to long ago about a helicoil fix and it melting a plug..

 

try loading up a factory tune and see how she runs. you've got a programming issue it sounds like

also, the COP's on the mod motors are very very very...picky...Use OEM Motorcraft only. Pull 1 at a time and see if the miss moves. Then only replace that one.

 

Checked on wide band today. 12's from 1/2 throttle to full and 14-16 from 1/2 to idle. Alittle lean at low rpm but ok. Changed tune, added fuel and returned low rpm range to 0 timing. After a few miles, miss returned intermitently. Maybe crap coil packs after all?