n14 cooper s manual. i have high negative fuel trims (long term at -18% consistently). with no codes stored whatsoever. no boost or vac leaks. only problem is jerky low throttle response and it's even more pronounced at driving just after i start the car and lasts for about 15-20 seconds (hot or cold engine doesn't matter). so i zeroed in on injectors. last mech worked on my car was somewhat sketchy and he said that he cleaned the injectors; i am thinking that he probably did something wrong. so i am planning to change them.

my question is, if i buy 13538682350 bosch injectors, new in box, are they plug and play or do i have to resize the teflon seals? pelican article states that i need the resizing tool "if i am reusing the old injectors" but people on comment section have different opinions. so i am confused.

please help me.

 

I believe you only need to worry about the Teflon ring if you are reusing the old injectors. Since you plan on buying new injectors, the Teflon ring should already be in place, and not be an issue.

Are you sure your issue isn’t related to a failing high pressure fuel pump?

 

negative fuel trim means too much fuel or/and not enough air. i read in a bmw forum that if hpfp fails in a way to dilute engine oil with fuel, it might cause negative fuel trims. but bmw engine has different hpfp design and my fuel trim doesn't budge after fresh new oil change. everything points me to the injectors.