Welcome! Hard to tell what’s going on just driving around the block. Usually better diagnosis with pulls in 3rd gear 2500-6000+ rpm, shifting to 4th. You’ll be hitting 90 mph+ so please be mindful of others. Are those JB4 parameters in the Datazap? I think most people on the forum speak MHD. Also any codes?
Keep in mind: maintenance before mods. Understood you got the car as-is with some mods on it. Did you happen to get its maintenance history? Here are the key things to look for / maintain in N54s (I’ve had my 2008 335 xi AT since new, now 72K miles and meticulously maintained):
1) oil leaks around oil filter housing and oil cooler housing. Notorious for getting on your belt and potentially causing the belt to degrade / fly off / get sucked into the engine behind the flywheel.
2) walnut blasting of intake valves - usually every ~15K miles, depending
3) fuel injectors - are they 12s? Installed correctly? Any blow-by?
4) Oil changes and filter every 5K miles, depending
5) coolant changes every 30k miles
6) AT transmission oil change every 30k miles, depending.
7) AT solenoids and seals every 60-80k miles
8) Transfer case oil change every 30k miles (if x-drive / not you, luckily)
9) differential oil change every 60k miles
10) engine mounts, especially the right one next to the downpipes that fails first because it gets so hot there. It will affect how the engine lines up with your AT tranny and if sagging will induce timing pulls, I believe. Replace it with the one for the 1M car and wrap it in gold hot foil (I did this).
11) Coolant pump (get the aluminum one) and thermostat every 60K miles.
12) Replace the stock radiator (they all eventually leak before 100K miles) with all-aluminum like CSF. Mine failed at 70K miles last winter. Typical plastic side mount failed where it’s bonded to metal).
13) Spark plugs as needed. Plenty of discussion here on which ones / which gap / which coils etc.
14) One more big oil leak to keep an eye on: the oil pan gasket. Huge PITA
, especially on xi which is best done by removing the subframe (e.g., the wheels, brakes, axles, pedestal, and front diff. But while it’s all off it makes working on the turbos / exhaust and water pump and thermostat easy-peasy… ask me how I know.)
15) …? N54 Veterans: what other maintenance items shall we advise our new friend to consider?
So please report back after you’ve taken care of all of the above items, installed MHD, and do some good pulls.
We look forward to working with you.
Again, welcome!