[DoomedE90]

I bought an e90 N55 335xi this year and I kept my daily. About a month ago I was fueling and I put 87 in it instead of what it’s tuned for (93)- without thinking that it's NOT the daily!!

The car started misfiring a bit. I could hear it burping clearly. Fast forward and talking to the guy that tuned it (stage 2+) on what I should do, he recommended I refuel it with E85 when I get to half tank. Then run that tank and all should be good. So, I put in 4 gallons of E85 and then topped it off with 93 (came to be another 4 gallons to top it off). The misfiring got worse the more I drove it and the engine light finally came up, misfire on cylinder 6.

We drained the tank and put new sparks. I drove it for over 100 miles and the car still misfires.

We pulled out the fuel injectors and the one in cylinder 6 was missing it’s O-ring. It is worth mentioning that when we took the injectors out we were surprised that "Mr Trusted Mechanic" (the guy that tuned it) did not install the decoupling elements when he replaced the injectors last year (2023)!!

We borescope it and nothing was inside the cylinder so we just replaced all injectors in hopes that everything will go good. The car still misfires, same code after less than 10 miles!! What should I do?

I just cannot wrap my head around these questions:
1- How did the car run for a little while when the injectors were installed with no decouplers with no issues?
2- How would the wrong fuel cause much more damage than the injectors sitting inboard?
3- Where did the O-Ring disappear?
4- What could be the issue now? I replaced all injectors but it is still misfiring!

[lookalikehuuh]

Its pretty likely the injector holes are out of round now and aren't holding pressure properly, causing the misfire. This happens because the decouplers are missing and the injector essentially bounces around in the head and ovals it out. Sounds like Mr. Mechanic will need to replace the head for you.

There is a company that makes threaded inserts, but they are apparently somewhat problematic from what I have seen. So replacing the head is the correct way to fix the issue.

[DoomedE90]

Unfortunately Mr Mechanic did the work for the previous owner so that’s not an option.
I just couldn’t connect the fuel issue with the holes going out of round all of a sudden! But if you’re right, I looked at those threaded inserts and it looks like all the reviews are positive. Is there an issue with those in the long term?

Thanks!!

[hawkinsli]

Same problem as well, I have already changed all 6 injectors into index 12, but misfire still there, my mechanic suggest me to change the ECU...

[lookalikehuuh]

Originally Posted by DoomedE90

Unfortunately Mr Mechanic did the work for the previous owner so that’s not an option.
I just couldn’t connect the fuel issue with the holes going out of round all of a sudden! But if you’re right, I looked at those threaded inserts and it looks like all the reviews are positive. Is there an issue with those in the long term?

Thanks!!

While I don't know anyone directly that has those inserts, I have seen multiple posts with problems with fitment of the injector in the insert and the inserts backing themselves out after some time causing more issues.

[DoomedE90]

Originally Posted by hawkinsli

Same problem as well, I have already changed all 6 injectors into index 12, but misfire still there, my mechanic suggest me to change the ECU...

Let me know if that works for you!! My engine light went off somehow. The car is still misfiring but it’s much better now. I’ll throw in some injector’s cleaner and see if that helps it before I do anything else.