06 century 12.7 60 intermittently going in to sort of limp mode

your egr valve if I’m not mistaken opens when it’s not at wide open throttle and closes when it is, it also closes at a certain altitude to give you full power at all times. I think it was 8000 Feet.

now having the Egr valve welded shut doesn’t do anything because the computer thinks it’s working and compensates the fuel mixture to match. Your first issue you need to fix is the delete. That I can’t tell you how to do because of forum rules.

 

I’d check boost sensor also, it’s probably the cheapest fix.

 

It sounds like the variable turbo vanes are not responding correctly. check to see if the clevis is still there, and not stuck (on the turbo). the air leak you describe leads me to thing the V-pod is faulty. If you're not sure, take it to a shop

 

It's possible to adjust the turbo and take the vpod out of the equation. It should be used as a test only, just adjust the turnbuckle to the turbo open but count the number of turns so it can be put back. The issue is if it's always at full boost it can damage /overspeed the turbo.

 

14l was available 1998/1999.

 

Wasn't aware, knew guys that had 1998 and a 1999 freightliners with 12.7's

 

Did u found out what was ur issued? .I'm having the same problem outhere