The air filter cover on my Disco (4.6) was bad as the clips on both sides cracked. I ordered a new cover and a new MAF sensor only to find out that they were for the 4.0 engine. Not an issue--the actual MAF sensor is the same part # for both engines, and I procured the rest of the intake that goes from MAF to the throttle body. Right of the bat she started idling freaking awesome. Purred like a kitty.

After almost 2,000 miles in 4 days, I noticed several things:

1. Idle is smooth
2. Power delivery is awesome
3. Long term trim is -18 in both banks
4. Fuel economy dropped by .5 MPG

Not sure how much of this is attributed to going cross country and driving at the high elevation, but negative LTFT throws me off. From what I gather, the ECU needs to adapt to the new MAF, but how long should it take? Also, could the 4.0 air intake setup be that much incompatible with a 4.6 engine?

By the way, the 4.0 design is odd... Not sure if I keep it even if the fuel trim is sorted out. The electrical connector that attaches to the MAF sensor is 1/4" away from the tube that goes from the radiator.

 

I’ve used 4.0L intake tubes on 4.6L’s for years with zero problems. Normally after a MAF swap you’re “supposed” to clear the adaptive settings. 90% of the time you can just swap it out and notice no real big difference. The MAF clips that the Airbox uses to attach to has some play in it, so just rotate it up a little away from the radiator hose.

 

^ Thank you for the tip. Rotated as much I could and now there is a 1" clearance. Still the trim numbers are pretty negative, about -16... Any other ideas?