Hey Swagga, thanks. I never heard of JLT until you brought them to my attention. Thanks, man. You also saved me some coin!
Me neither. I was not going to do an intake on this vehicle but I may now.
As far as the intake leaning out, in closed loop, any leaning out will be countered by the long and short term fuel trims to keep it running at or around 14.64. On other vehicles, the computer will use the last range of fuel trims to account for everything above that maf range (open loop). So if you start with an intake and the fuel trims make up for it by adding say 10% fuel to maintain 14.64 after a few hundred miles of driving, then you go into open loop or wot with 10% additional fuel over what the tune calls for. This will end up accounting for any additional air the intake provides. So on a car that has settled LTFTs, the additional air from the intake won't cause a lean condition assuming no tuning is being done.
That is, in the case that the open loop maf range on this ecu gets its corrections from the final closed loop maf range (40-60 or so g/s of air). If this ECU were to just revert to the actual maf scale without applying any corrections then it would cause the vehicle to lean out if stock maf scaling is used with an intake. I can't see how a company that has to warranty these engines would allow this to happen with the stock tune though.
In either case you will get far better results by tuning the vehicle and if you're going to tune it, add the intake before you do and account for it in the tuning. I don't have any experience with 5.4l tuning, but I would be shooting for somewhere between 12.5 and 13. I would go as lean as possible and then set timing to accommodate the leaner mixture, rather than set a safer mixture as a crutch for more timing. That's not to say that adding timing is bad but I would dial fuel in first and then set timing to the knock threshold and then back it off between 1 and 2 degrees.
One of my tuning goals for my cars is always the smoothest possible idle/drivability. I've had good luck with changing the closed loop fuel targets to be closer to 14.2 than 14.64 and smoothing the fuel table around the transition from closed to open loop and matching it to the open loop table at that point.
I'm really anxious to get into my expeditions tuning and wish there were better open source options to do it. I'll eventually probably shell out for the SCT and then the SCT software. This is really hard for me to justify on a 99 with very little value.
Specifically to the topic though, I don't think I would go with anything that didn't offer some ability to tune and data log, be it with additional software or direct to the device and transferable to a computer. Canned tunes are too general in most cases and the results very greatly from vehicle to vehicle. Based on my research here, if you're going to tune it yourself start with the SCT, if you want it tuned correctly, buy the SCT with a custom tune from one of the vendors here. I believe 5 Star is a popular choice as well as a few others.
