Broken down for an easier read.
Quote:
Originally Posted by 2_Spools_919
Hope this post helps someone out.
To start, I work at a repair facility that works on BMW's.
The last car I worked on this week was a stock 2016 Z4 w/ N54 and 62,0000 miles.
- The car came in for a check engine light and running rough on cold start.
- So we parked the car and let it sit to perform a cold start.
- On cold start the vehicle barely wanted to run, it had a very lumpy rough start.
Then while connected to ISTA, and monitoring the O2 sensor status, once the O2 sensors became active the idle smoothed out but the multiplicative values were at 30% for banks 1 & 2 with fault codes 29E0 & 29E1 mixture control bank 1 & 2 too lean.
So, with them both banks at 30% and almost identical, the thought process was, it has to be something that affects both banks together.
- So we smoke tested the intake system. We found the rear turbo inlet had a leak at the flange and the charge pipe was leaking. So naturally, we replaced the leaking turbo inlet and charge pipe. smoke tested and no leaks.
- Checked multiplicative values and still at 30% for both banks.
Let me not forget to mention that the previous week the vehicle was towed in for a no start, and we found that the low-pressure pump was only putting out 30 psi. After replacing the low-pressure pump and regulator, the high-pressure pump and rail pressure sensor were replaced for rail pressure plausibility faults.
So at this point, the low-pressure pump, fuel pressure regulator, high-pressure pump, charge pipe, and bank 2 turbo inlet have been replaced.
No unmetered air leaks. We smoke tested the crankcase through the oil filter cap and sprayed the entire valve cover with soapy water to check for any small cracks or leaks and none were found.
We measured crankcase pressure with a digital manometer and it was spot on at 17mBar. So, we disconnected the tank vent valve from the throttle and plugged the port and no change in the values they were still at 30% both banks.
So, the next step was O2 sensors.
- We replaced all 4 O2 sensors and crossed our fingers. Nope, values still at 30%.
- We flashed the DME with ISTA/P and allowed vehicle to sit overnight. Started it up in the morning and it ran rough again until the O2 sensors were active and the values shot up to 30%.
- We swapped the map sensor with a new one and still 30%.
So now the last thing we thought it could be were the injectors.
- They were all index 12. Surely it couldn't be the coveted index 12 injectors.
Luckily, this customer has a good extended warranty. The warranty company has been on the hook for all of the repairs. So, we called in the claim and they approved it.
I installed 6 new fuel injectors and calibrated with ISTA.
Started it up and right away, the cold start was no longer lumpy and rough.
While at idle without driving the multiplicative values were at 12%, a dramatic improvement. So we took her out for a good test drive.
- Checked the multiplicative values afterward and they were at 2.27% bank 1 and 4.97% bank 2 and the mixture faults were no longer present.
I was really surprised that the injectors were the cause of the mixture faults with them being index 12.
Maybe something passed through the fuel system and was restricting flow
Not sure, but visually the tips of the injectors did not appear to be full of carbon.
Anyhow, this has been a long post. Hope it helps someone.
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