I'm just getting into the whole EFI world. playing with a new to me 98 Dakota with an EFI 5.2L that's got some light mods (cam, intake, headers)

I'm working with an SCT engine tuner who will write custom engine tunes for the computer, using a data logger and O2 sensors to dial in the tune.

assuming that it's possible, I'd like to throw as much timing and fuel at it as possible during WOT, but cut way back at part throttle cruise.

I know that at max power you want a ballpark of 12-13:1 AFRs

but what about economy cruise? how much timing is ok, and how lean can you go? I'm thinking that if he can program it, I'd like to see as much as 50 degrees advance at part throttle cruise, and maybe as lean as high 14, low 15 to 1 on the AFRs.

how much advance do the vacuum advances give on the old engines? if you're running 36-38 degrees mechanical all in by 2500, and the vacuum advance is hooked up, how much is the total timing under part throttle cruise?

and how lean can you realistically go without hurting anything, when under part throttle and light loads?

With a stock computer, even recalibrated, your part throttle cruise is going t be 14.7 because the computer is designed to run part throttle at stoich off of a narrowband o2 gauge. The only other option would be to disable closed loop o2 monitoring during cruise but I somehow doubt your tuner will do that.

Stock mechanical advance distributors + vacuum advance could give you a total advance in the low 50's at a steady cruise. However the magnum headed engines will require less timing at cruise than the old open chambered engines of the 70's.

the guy writting the SCT programs for me said he can force it to stay in open loop. I was asking about possible future upgrades, to include a 5.9L swap with a cam ground on a 106 LSA. he said "no problem, we can do it, but I'd have to disable closed loop because all the overlap will make the computer think it's running rich when it isnt."

I'm not sure how much he can manipulate the stock computer though, if it is going to maintain the factory set calibrations on AFRs etc.

right now I've got to figure out what's making the computer pull the IAC wide open when I let off the gas--something in the timing and vacuum signals must be making the engine think it's about to stall out, and it opens up the IAC so wide, it holds a 3000 rpm idle while the truck is still rolling, but once I come to a full stop, the idle drops back down to 750.

I put it into neutral or step on the clutch, and the RPMs drop from 2500 to about 2,000 then the IAC slowly opens fully and it gradually climbs back up to 3000 rpm on the "idle"