Possible fault cause
- A valve does not switch to large lift
- Several valves (various cylinders) do not switch to large lift
Diagnosis/troubleshooting
Perform system test for large lift
WARNING: Test is carried out while driving. Have a second person operate the Porsche System Tester 2.
During the system test for large lift, the valves remain at large lift, regardless of the type of driving. Faulty switching conditions can be detected by
rough running, just like with misfire detection. If a valve is not switched to large lift, the fault type 'over limit' is recorded.
Several cylinders may be stored as faulty, although only 1 valve on one cylinder is faulty.
In order to guarantee safety during repairs, the flat-base tappets of the inlet valves of the entire cylinder bank should be replaced if a fault occurs.
A faulty flat-base tappet can be detected because the oxygen sensor F(R) for this cylinder bank hardly changes the mixture at all given acceleration
with wide-open throttle (F(R) at 1) and enriches the mixture in the opposite cylinder bank (F(R) > 1) - see drawing below. Given a difference
between F(R1) and F(R2) of more than 8 % during acceleration with wide-open throttle, a fault is certainly present.
If the difference is less than 4 %, 1 valve may be faulty on both cylinder banks. In this case, all flat-base tappets of the inlet valves must be replaced.
1 - Select system test.
2 - Select 'Request large lift'.
If "Valve diagnosis not ready" appears, a fault may have been stored.
1. Erase the fault memory.
3 - Activate the system test with the key F8 immediately before acceleration with wide-open throttle.
The message "Drive link active" then appears.
4 - Perform acceleration with wide-open throttle in 2nd gear, until "Valve lift diagnosis complete" appears.
NOTE:
- If a fault is detected, it is only recorded in the fault memory after 6,000 ignitions (at idling speed approx. 3 minutes waiting time).
- It is important to observe the oxygen sensor during acceleration with wide-open throttle or to record its behaviour with the data logger.
- If misfires are stored, see Troubleshooting misfires.
630 Valve lift control, cylinder 4 - below limit
Diagnosis conditions
- Speed between 2,000 and 3,320 rpm