FAQ
TL;DR: In this BMW E90 N46 case, 1 of 4 Valvetronic springs failed—"one of the four springs snapped"—causing a top‑end tap; replacing the springs and timing restored smooth power. [Elektroda, Saimon46, post #17403540]
Why it matters: For BMW E90 320i N46 owners and techs, this FAQ speeds diagnosis of post‑trip or sudden top‑end tapping and points to proven fixes.
Quick Facts
- Symptom band: tapping appeared between approx. 1200–3000 rpm and started 3–5 minutes after a cold start. [Elektroda, Saimon46, post #17218116]
- Confirmed fix here: one of four Valvetronic springs snapped; replacing all four and redoing timing resolved it. [Elektroda, Saimon46, post #17403540]
- Vacuum pump can also knock; rule it out before deep cylinder‑head work. [Elektroda, helmud7543, post #17403379]
- No fault codes were stored despite the noise; mechanical faults may not set DTCs. [Elektroda, Saimon46, post #17218116]
- K&N E‑2021 panel filter was used; driver reported better response and sound. [Elektroda, Saimon46, post #17404834]
What’s the most likely cause of top‑end tapping on an N46?
In this thread, the proven root cause was a failed Valvetronic spring. The owner reported “one of the four springs snapped.” Replacing all four springs and refreshing the timing eliminated the tapping and improved acceleration and sound. Start by inspecting the Valvetronic hardware before assuming bottom‑end issues. [Elektroda, Saimon46, post #17403540]
Is it safe to keep driving with the tapping noise?
No. Park it and diagnose. A mechanical valvetrain fault can escalate to major damage if you continue driving. As one member put it, “I would not risk it.” Transport the vehicle to inspection rather than running it. [Elektroda, sebap, post #17219964]
Could a failed vacuum pump cause similar knocking?
Yes. The N46 vacuum pump can knock and imitate valve‑train sounds. “The vacum pump may also knock,” noted a contributor. Inspect the pump for play or internal damage before committing to cylinder‑head repairs. Replacement is straightforward and a useful elimination step. [Elektroda, helmud7543, post #17403379]
How do I check or reset ECU adaptations after intake or timing work?
Adaptations are the ECU’s learned fuel/air adjustments. Reset them after intake or timing changes so the ECU relearns correctly. “Adaptations are adjustments to the factory dosing maps of the fuel and air mix.” Use a BMW‑capable scan tool to clear them, then road‑test. [Elektroda, helmud7543, post #17403379]
Did the long 600 km trip cause the problem?
The noise appeared right after a 600 km sea trip and a restart. That links the timing of onset, not causation. Use the trip detail as context, then diagnose the valvetrain and vacuum pump to find the actual fault. [Elektroda, Saimon46, post #17218116]
What exactly fixed the OP’s car in the end?
Replacing the failed Valvetronic spring set solved it. The owner installed four new springs, refreshed complete timing, changed oil to Motul 5W‑30, and added LM Ceratec. He retained a K&N panel filter. The engine’s response and sound improved markedly after the repair. [Elektroda, Saimon46, post #17403540]
I opened the oil cap and heard dull knocking. Is that normal?
Yes. Opening the oil filler cap introduces unmetered air. RPM can drop or rise, and noises can change. An expert explained it clearly: the engine may “work badly after opening the oil plug… finally the left air gets.” Refit the cap and reassess. [Elektroda, helmud7543, post #17403379]
Why are there no fault codes even with loud tapping?
Mechanical issues in the valvetrain may not set diagnostic trouble codes. In this case, the ECU reported zero errors despite a clear tapping noise. Investigate mechanical components when symptoms persist without codes. [Elektroda, Saimon46, post #17218116]
Which K&N filter fits the E90 320i N46?
K&N E‑2021 fits. The owner reported a crisper throttle and sportier intake sound after installation. If you use an oiled filter, follow the cleaning and re‑oiling instructions precisely to maintain performance. [Elektroda, Saimon46, post #17404834]
Should I revert to the stock air filter when diagnosing?
Yes. A/B test by refitting the previous filter to isolate variables. A member advised, “try to put on an old one.” This helps confirm whether intake changes affect drivability or sound. [Elektroda, chiqi, post #17220014]
Are N46 engines prone to camshaft wear or Valvetronic failures?
A contributor noted camshaft wear is not typical for these engines. Valvetronic failures are a known fault and can be costly to repair. “Worse as valvetronik is falling apart—renovation here will be expensive.” Prioritize Valvetronic checks for top‑end noise. [Elektroda, helmud7543, post #17403379]
Is there a head‑lubrication issue behind this symptom?
Not in this case. The investigation did not find a lubrication defect. The confirmed failure was a snapped Valvetronic spring, addressed alongside a timing refresh and oil service. Focus on Valvetronic hardware first. [Elektroda, Saimon46, post #17403540]
How can I triage N46 tapping before running it again?
Do a quick staged check:
- Inspect the vacuum pump for play/noise and replace if suspect.
- Remove the valve cover; inspect Valvetronic springs for breakage.
- After repairs, clear ECU adaptations and road‑test.
These steps isolate common causes fast. [Elektroda, helmud7543, post #17403379]
Is K&N better than other brands on the N46?
This thread offers no comparative data. It only reports that the K&N E‑2021 felt more responsive and sounded sportier. Choose a filter you can service correctly and that fits your maintenance routine. [Elektroda, Saimon46, post #17404834]
