Hi all and thanks for reading.

I did an 0411 swap into my 4x4 99 OBS Yukon with a mildly massaged L31 vortec about a year ago.

First, the L31 has TrickFlow heads adapted ( had to drill for the vorted vertical intake bolts and drill for center bolt valve covers), mild Comp Cams rv cam (pulls from about 1500-5600), short tube headers no cats (offroad only of course), stock intake with MPFI spyder mod.

Runs great, I will say the 0411 swap added nearly as much pop as the other mods combined, really!

The only problem I have is on startup, the engine hunts really bad until I let it idle for about 30 seconds until it figures out where it's at... mostly when dead cold or after it's real warm. The black box that replaced it cranked right up and idled kinda pretty from the get go.

I'm pretty new to efilive so I barely know how to log some parameters to playback and look at what's happening. I have the timing jumping around pretty severely and actually was moving from 0deg to 20ish deg when it does it's dance.

I limited the minimum advance from where it was set, -14deg min to +14deg min and it changed it a little, seems to be running pretty rich, I can smell the raw fuel when it does this but don't know how to track the fuel mix before the 02's are online, and by that time it's sorted itself out. I don't have a wideband. I also noticed lots of stuff the original blackbox didn't have like decay stuff, where I think it starts with some number and goes to a more normal number at a rate determined by crankshaft rotations. All of these "decay items" seem to state something about a 24 tooth reluctor (os from a 2002 L31 express van) and the Vortec has the the original 4 tooth with the crank position sensor in the stock place.

I've been driving it for nearly a year like this, minor annoyance at worst, but now I have some time to address this issue.

Of course I'm an oldude and been tuning cammed up carbureted engines for at least 45 years and decided to add another wrinkle to my brain with this EFI stuff. I'm enjoying it but would now like to fine tune (pun intended) my skills.

Thanks in advance for any help, jeering or even snyde remarks