Vortec 7400 MAP/Timing issue.

[Philip Parker]

Hey there - I put a brand new top end on my old Vortec L29 and for the most part it runs pretty good. I am however chasing a weird problem. 

 

As the engine heats up the MAP readings creep up, and as a result the ECU starts pulling timing like crazy until the truck creeps along a low RPM (like from a stop sign). 

 

It's got a good tune, and when cold the truck runs super strong. My inital guess is of course a vacuum leak, however I have smoke tested it multiple times and found nothing. Anyone ever experience this problem? There are forum posts all over the internet about this exact issue but I cannot see any post that found a fix. 

 

Thanks in advance 

 

Philip