The original BMW 335i is a bit of a marvel. At the time of its release, everyone thought BMW had gone mad. Why sacrifice the character of a naturally-aspirated engine when the German marque could’ve just built a modern version of its M30 big-six? Well, it wasn’t long until drivers noticed smooth, almost lag-free power delivery and tuners realized they could add the better part of 100 horsepower with a few bolt-ons and a tune. How’s that for a bit of humble pie? However, as these cars depreciated, it became apparent that they were quite expensive to keep going, and over the past few years, the costs have grown much higher.
Really, it’s not just the 335i I’m talking about – it’s anything with the N54 twin-turbocharged inline-six engine. Certain years of 135i, 135is, Z4 sDrive35i, Z4 sDrive35is, 335is, 535i, X6 xDrive35i – all that stuff. The N54 is a neat engine, but almost everything bolted to it is terrible. The turbochargers develop wastegate rattles that require serious hours to repair, the plastic valve cover cracks, the charge pipes leak, and the high-pressure fuel pump can go bang. However, most of these pale in comparison to the issue of fuel injectors.
The N54 uses piezoelectric direct fuel injectors, and because it’s a fairly early application of this tech on a gasoline engine, they tend to go a bit wrong. BMW had to revise injector design 11 times during the engine’s production, eventually landing on the latest Index 12 injectors. However, Index 12 injectors can still fail, and you’re not ready to hear what each replacement injector costs.
Take a deep breath. From reputable online retailer FCP Euro, Index 12 injectors for the N54 inline-six cost $549.99 each. Yes, each. What’s more, it’s not recommended to mix Index 12 injectors with Index 1-10 injectors as a calibration change occurred for Index 11, which means that it’s recommended to replace injectors bank-by-bank. Considering an N54 has two banks of three cylinders, this means a minimum outlay of $1,649.97. If you want the peace of mind of replacing all six in one go, that’s $3,299.94 worth of fuel injectors. That’s enough to mechanically total a high-mileage E90 335xi.
Index 12 injectors weren’t always this expensive, so what the hell happened? In short, there was a parts structure change. The updated fuel injectors for the N54 engine carried a part number of 13538648937 and were made unavailable outside of recall or warranty work in 2018. However, they were basically identical to the then-recently updated direct injectors found on the S63 V8, part number 13538616097. Both part numbers have since been combined under part number 13538616079, still identical to the injectors on the S63, albeit much more expensive than before.
So are there any aftermarket alternatives to these pricey VDO-manufactured injectors? Yes and no. There are companies out there that promise to rebuild these fuel injectors. However, rebuild quality varies wildly, so it’s a roll of the dice on whether you’ll need to just buy brand new injectors anyway. I’d also advise against ordering cheaper injectors from eBay as many are counterfeit with improper calibration values printed on the parts. As replacing N54 injectors requires registering the new injectors in the engine control module, punching in correct injector calibration values is critical to avoid misfires.
As it sits, there is no cheap way to properly replace N54 fuel injectors according to servicing guidelines. It’s a painful reminder that once-bleeding-edge technology will always be expensive to keep going as few first shots are ever perfect. If you’re in the market for an N54-powered BMW, it’s a good idea to ask for service records and see if the injectors have ever been replaced. If all six are now Index 12 injectors, you’re likely in the clear. If not, be sure to keep a few grand lying around for when the inevitable happens. Really, that’s good German car advice in general.
Lead photo credit: BMW