[tsmoove24]

okay all
I've been chasing down a jerk under acceleration in my 2009 335i xdrive 6 speed manual for the better part of a month.

car has about 76600 miles on it and saw regular service through its life. i Bought it a few months ago with 73800.

about a month ago i started noticing small jerks under acceleration in gears 1 2 and 3 at about 2k-4k rpm.
At first i was suspecting a transfer case issue because i had brand new tires up front and tires at the wearbar in the rear.
rear tires replaced and issue still occurred

i moved on to beliveing it was a misfire but the car wouldn't throw any codes or lights on the dash.

i pulled all my plugs and bmw was written on them so i believe they are original with 75k miles at the time.
additionally my cylinder 4 plug was fouled and smelled like fuel.
i went ahead and replaced with the 1 step colder plugs with a 0.0275" gap with feeler gauges. (gap for stock cars- mine is bone stock)
the issue didn't get any worse or better after putting in the plugs.
started reading live misfire data and i read multiple cylinder 4 misfires (only 4 for 20 minutes worth of driving and idling) along with a misfire or 2 on a few other cylinders.
my coil packs were shown replaced in the carfax around 50k miles but i noticed 4 were bosch and 2 were delphi.
i got 2 new bosch coils to test with and to make a matching set.
with live misfire data i still saw a misfire or 2 on the cylinders with new coils so i moved to injectors.

i bought 7 remanufactured index 12 injectors with flow tests from a guy who cleans out storage unit.
injectors looked legit.
i than pulled injector 4 and saw crud built up on the tip and replaced and programmed an index 12 for cylinder 4
the acceleration misfire didnt go away so i threw the other 5 index 12s in
cleaned my intake valves (certain cylinders had and 1/8" of carbon buildup on the walls)
i programmed the 5 new injectors and reset the adaptations.
started the car after that and got some throttle adaptation codes and a crazy bouncing idle but got it figured out with a manual throttle body adaptation.

the car pulled the best it had in weeks but still misfired a couple times during a moderate pull from 2500-4500rpm.
still no codes
i've worked on some backfoot guesses since and have gotten to where i am now
-checked coil pack grounds
-looked at my dme wiring connector but noticed it was a msd81 and didn't see any obvious wiring issues
-cleaned my vanos solenoids and they both still rattle and appear to be functioning
-closely inspected my valve cover for any hairline cracks (couldn't find any


my only guesses right now are
-leaky injector (have already swapped in my extra index 12 to cylinder 6 which had the most fuel smelling plug- no change)

hfpf- normally codes associated with failure - doesn't take extra time to crank but i do belive it's original

lpfp- no gas smell from the cabin and again no codes but believed to be original

lpfp sensor- have read online it can cause a misfire but most of the times there's other symptoms and codes

mosfet/dme failure - i'd have to pull out the dme and test mosfets but i've been pushing it off since it's the improved 81 dme

highly confused as misfire data still reads 1-3 misfires on 4 out of 6 cylinders but the misfire numbers are never consistent with the previous scan.

sorry the long story
i am a trade school student and have access to a fair amount of resources and snap on scanners which is what i've pulled my misfire data with so far.
I have a little bit of experience with german cars and am in school to further my education. my repairs are done relatively by the book with torque specs and new qaulity partys (aside from the injectors i bought used)
I don't have any means to pull a log but will probably look into a better scanner that's capable for me personally soon.

any help would be greatly appreciated
will attach what my cyl 4 plug and injector looked like along with the rest of my injectors and some misfire data i took after a each repair.

[whyzee125]

Highly unlikely it's a mosfet issue as you're MSD81--as far as I know those failures are only on MSD80.

Have you tried a firmware update to the DME?

If you're confident none of the injectors are leaking (there's a good youtube video on how to test them. Basically invert them so they shoot to the drivers side and crank the car for a while with the wires unplugged), I'd do a compression test and boroscope the cylinders next.

[tsmoove24]

Originally Posted by whyzee125

Highly unlikely it's a mosfet issue as you're MSD81—as far as I know those failures are only on MSD80.

Have you tried a firmware update to the DME?

If you're confident none of the injectors are leaking (there's a good youtube video on how to test them. Basically invert them so they shoot to the drivers side and crank the car for a while with the wires unplugged), I'd do a compression test and boroscope the cylinders next.

thank you so much for your input


i have not tried a firmware update but will look into what it takes to get one done.

i'm waiting for a morning that i have some extra time to pull all my plugs again and check for fuel smell or wetness as well as try the inverted injector test.

compression and leak down tests were definitely in the plan down the road but i didn't make a point to do them right away as the misfires haven't stayed consistent on one cylinder.

i have about 400 miles to drive this weekend that i'm hoping to get through issue free. hasn't given me any issues getting to school, work and around town since the issue started. once im back i'll get right to work on your suggestions