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      10-03-2012, 03:46 PM   #18

Drives: 03 Turbo Cobra, 2011 335xi
Join Date: Jun 2010
Location: Wallingford CT

iTrader: (3)

Originally Posted by Verbatim View Post
My car was misfiring in cylinders 5 and 6 and so the dealership decided to replace all the injectors under CPO warranty.
My question is, why are the fuel injectors failing? Aren't they supposed to last the life time of the car?
(and why does it seem like cylinders 5 and 6 are always the most problematic? )
Injectors do not last the lifetime of a vehicle. This isn't just for BMW, this is for all manufacturers. Injector failures are not uncommon on all platforms across the board.

Originally Posted by Verbatim View Post
I've actually had the recall done before, so there must have been some reason they needed replacing. (the car wasn't misfiring for no reason)
Does it have to do with carbon build up on the injectors that cause them to spray unevenly?
It has nothing to do with carbon buildup on the injector. The injector does not get carbon build up on it.

Originally Posted by blisstik View Post
They may have replaced them so they can get paid for the labor.
That is totally untrue. I will tell you why the car got 6 injectors. The test plan for misfires is very specific when using the BMW equipment. It looks at a few different variables. Some are symptoms (i.e gas smell etc), production date and what part # injector is in the engine. From there the tester will tell you based on the diagnosis which injectors to replace. Typically if you have 1 or 2 cylinders misfiring on the same bank, the tester will have you replace ALL injectors on that bank. It will then ask what part # injectors the opposing bank has installed. If its an older # then it has you replace that whole bank as well. It has nothing to do with the dealer trying to get more labor nor the tech doesnt know what he is doing so he just "shotguns" 6 injectors into the car.

Originally Posted by GeorgiaTech335coupe View Post
I'd imagine they have a very low tolerance for error, which can be somewhat supported by the fact they need to be coded which I believe is to accomodate minor manufacturing inconsistencies.

If it makes you feel better, I have only 60k miles and cyl 1 is on its 4th inj, cyl 2,4,5,6 are on their 3rd injector and cyl 3 is on its 5th injector.
They needed to be coded because each injector has a unique "flow rate" so to speak. They have Piezo crystals inside of them and each injectors tolerance is slightly different. So the DME needs to be coded to know which injector is in which cylinder based on the # stamped on the injector.

Your cyl #1 issue may also be a carbon buildup issue on the intake valves. This can cause misfires and misdiagnosed as an injector problem at times.

Originally Posted by psmitty95 View Post
I just bought one injector to fix my misfires in cylinder 3. I wanted to do all 6 but don't have the money to do that right now. I should also probably get a carbon cleaning soon since i'm at 51k miles...
Did you have the injector recall done? If so do you know how many injectors they replaced? ( you do not automatically get 6 new ones FYI) Also if you need a carbon cleaning done shoot me a PM I can help you out.