Case/004

BMW 335i

Intermittent loss of power

Cause: A hairline split in the charge-air pipe that only opened above a certain pressure and temperature.
Outcome: Charge-air pipe replaced, boost system pressure-tested, adaptations reset. Re-tested over the same route. No recurrence.

Customer report
The customer described the car going into a flat, sluggish state for a few seconds at motorway speed, then recovering. It had happened five or six times over two months. Another garage had replaced the boost-pressure sensor without effect.
Initial data
One historic code for charge pressure deviation with freeze-frame data showing high load, high intake temperature and boost dropping to near atmospheric. No current codes.
Testing
We logged boost target versus actual, wastegate position and intake temperature while driving the route the customer described. Boost fell away only above roughly 1.4 bar with intake temperature over 45°C. A smoke test at operating temperature showed the leak; a cold test did not.
Cause
A split on the underside of the charge-air pipe near the clamp. Closed when cold, opened under heat and pressure. The sensor replaced earlier had been reporting the loss correctly.
Resolution
New charge-air pipe and clamps fitted, full boost system pressure test, adaptations reset. Re-driven over the same route at the same load. Boost held. The customer has had no recurrence since.

Similarsymptoms?

Tell us what the car is doing. We'll start from the data.