I've been fighting my high fuel trims for two years, now, and have never found a vacuum leak (smoke tested 3x, carb cleaner test 4x, visual inspections as well).The O2 readings have always been good.

My fuel pressure tested barely 50psi, but only had two misfire errors over a year back, and none since (the engine starts and runs smooth as silk), so it's probably not the fuel supply. Rebuilt the DISA, replaced the filler cap & gasket (the only possible leaks I ever found), and I'm fairly sure the CCV is OK (23+ psi vacuum while running, according to Torque Pro, no sign of Mayo).

I cleaned my original Siemens MAF, and still had very high fuel trims, then tried a $20 MAF from Amazon, and the fuel trims got much better (the MAF readings were much higher), and that's the way I operate it now...having never completely eliminated the high trims. I also bought a second $20 MAF (Amazon owed me a refund on another purchase), and I now have three onboard. My conclusion, at that time, was that the Siemens MAF was underreporting, but there's got to be something else contributing to the lean condition.

I haven't driven my X5 since July, and only ran static tests in the driveway this summer, so when I had a Dr's appointment today, I put two bottles of Liqui Moly Jectron Fuel Injection Cleaner into the tank (previously filled in July), and took a chance on the state emissions test a few days early (due by 10-31), since I was out and about. It passed, despite LTFT's between 7-11, and the short terms trying to balance them.

I should've driven the X5 a few hundred highway miles with the cleaner in the tank, and the trims would've been better, I'm sure (my mpg goes up considerably, and the fuel trims go down as well, on the very few occasions where I give it the old Italian tune-up).

My new take on the lean condition is my injectors aren't flowing very freely. I have no idea how old they are, and/or their maintenance history. I have had good luck using Lucas Injector cleaner on my GM cars over the years, but I have no experience using Liqui Moly, but I'll find out. Now that it's getting cooler outside, I'll start driving and testing the X5 some more...I'm determined to find the root cause of the high fuel trims before the next inspection in October 2024. Maybe using some Cataclean is in my future, as well.

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01 BMW X5 E53,3.0i-5L40E, 7/13/01
topas-blau,Leder-grau,"resto-project car"

Here:
14 Lexus ES350,3.5L-U660E
09 HHR Panel,2.2L-4T45E
04 Chevy 2500HD,6.0L-4L80E
98 GMC Sierra 1500,5.7L-4L60E

Gone:
66 Chevelle Malibu 2dr ht.,327>441c.i.-TH350>PGlide/transbrake
08 Cobalt Coupe,2.2L-4T45E
69 & 75 C10s,350c.i.-TH350
86 S10,2.8L-700R4
73 Volvo 142,2.0L-MT4
72 & 73 VW SuperBeetles,1.6l-MT4
64 VW,1.2l-MT4
67 Dodge Monaco 500 2dr ht.,383c.i.-A727
56 Chevy 210 4dr,265c.i.-PGlide