[1Kurgan1]

I had a new engine put into my 14' 550i xDrive about 6 months ago. I have about 8k miles on it so far and all is fine, except it has what to me seems like a minor misfire.

When it's started up I can feel it, average cruising it usually is not there. But on an incline it's can be felt, and when coast off the gas it can be too. It's super minor, but especially on decel almost causes a harmonization humming sound.

There has been not a single code thrown by the car since the new engine went in. And it has all of it's power.

So I guess it is not the end of the world, but it is an annoyance that seems confusing since it has no codes. I'm honestly not even sure where to start troubleshooting it because of the lack of codes. Does something this vague sound familiar to anyone?

[AnotherM]

The startup misfire sounds like an injector leaking.

I would start by hooking up a biactual scanner and watching the misfire counter. See if it actually misfires and if so what cylinder. Leave the scanner connected and try to replicate the misfire you feel.

Check the fuel pressure and monitor it as well as you drive up the incline.

If you determine you have misfires on one of the cylinders than move the coil from that cylinder to one that isn't misfiring. Hook up the scanner and see if the misfire moved with the coil. If it moved than you have a bad coil. If it didnt than switch the spark plugs and do the same test.

[1Kurgan1]

Well I had a chance to get it hooked up, 0 misfires detected on any cylinder. So not sure what the vibration is, their suggestion was many the aftermarket downpipes touch the firewall a bit which causes the resonation sound and feel.

Either way, no misfires, so I guess it's not a big deal.

[AnotherM]

If you decide to look into it further, I would suggest pulling your plugs and looking at them. You will be able to see if an injector has been leaking right away by how they look.

[1Kurgan1]

Originally Posted by F10c550i

If you decide to look into it further, I would suggest pulling your plugs and looking at them. You will be able to see if an injector has been leaking right away by how they look.

I had replaced the factory plugs just a few thousand miles ago with some colder plugs, they all looked normal. And the car got a new motor back in October and my mechanic did not notice any issue with injectors.

I doubt it's a misfire since none were detected. It seems like more of a resonation issue, could even be just from the missing cats. But I will keep it in mind.