X1 35i - Leaky fuel injector?

[cooked]

Hey All,

New here; not new to BMWs but this is my first N55.

Last fall my son and I picked up a neglected 2014 X1 35i for a great deal as a project to work on. It's been fun and we've fixed all of the common N55 issues, including replacing the VC, OFHG, both O2 sensors, and giving it a full and proper tune-up. We have almost 2k miles on our repairs, and the car runs great, has an even idle, no codes, no vacuum leaks, nothing odd, except that post fixing all of these things, the car now has a puff of dark smoke at startup, only when cold and only after sitting overnight. It's definitely not condensation and doesn't appear to be oil (not blue / greyish, and def looks dark like rich combustion), and is only there for an instant, possibly associated with the first fire of whichever cylinder(s) are rich.

Most likely it's a leaky injector, maybe due to disturbing the fuel system by removing the fuel lines over the VC and introducing some debris, or maybe just from age. Or it's possibly downstream of this (dirty combustion chambers that need to be walnut blasted; fouled cat from running with codes? Who knows....). As it does appear to be fuel, from searching around, likely next steps are to pull plugs when cold to see if any of them have fuel on them and/or are gas fouled. I'm hesitant to do this and just keep driving it to see if it cleans itself up, but before I go that route, I thought I'd make a post and see if anyone has chased this issue down previously. Rich is better than lean, but if this is an indication that there will be a bigger issue if left alone, I'll be more proactive in digging in.

Thanks and appreciate any feedback.

[wheela]

Do you have MHD for logging? One way to check for leaky injector(s) is to cruise down the highway and completely lift off throttle for a few seconds. Within a couple seconds your AFR should hit a hard limit of 234.something - I can't remember the specific number, but it's a hard stop with no fluctuation. If it doesn't do that, an injector is leaking. The caveat, I'm not sure of the sensitivity of this test. If it's a super slow leak that must sit overnight to accumulate, I'm not sure if you'll necessarily be able to detect it this way.

[cooked]

Thanks for the reply and insight. Yes, have the ability to capture logs and will give this a try over the weekend.

[cooked]

Originally Posted by wheela

Do you have MHD for logging? One way to check for leaky injector(s) is to cruise down the highway and completely lift off throttle for a few seconds. Within a couple seconds your AFR should hit a hard limit of 234.something - I can't remember the specific number, but it's a hard stop with no fluctuation. If it doesn't do that, an injector is leaking. The caveat, I'm not sure of the sensitivity of this test. If it's a super slow leak that must sit overnight to accumulate, I'm not sure if you'll necessarily be able to detect it this way.

Reporting back on this - Per your post, it must be a very slow leak, because the AF ratio behaves as normal throughout the vacuum range.

When we got this car it had most likely been run with a bad VC / PCV issues for quite a while, as there was oil in the vacuum line that runs to the exhaust flap, and the plugs and O2 sensors we pulled out looked like lumps of coal. Since we've repaired everything I'm almost wondering if it may clean itself up (dirty cat, oil at the exhaust flap), though an internal issue with an injector most likely will not self-repair.

It's possible that it may need a walnut blasting due to neglect, as DI also will not clean itself up if the valves are caked up with carbon. We probably should have done this when the intake was off for the OFHG, but thought we'd get it running first and get a baseline. Oh well, more work...