P0304
P0304
511 Misfire, cylinder 4
Diagnosis conditions
- A cycle of 1,000 crankshaft revolutions is evaluated (for misfire damaging to the TWC, 200 crankshaft revolutions). The misfire rates are compared with a threshold value. If the misfire rate is greater than the threshold value, a fault is recorded in the memory.
- The Check Engine Malfunction Indicator Lamp (MIL) is switched on and stays on when the misfire rate lies above the threshold value at which the emission limit values are exceeded during two consecutive driving cycles (in the case of EOBD 3 driving cycles).
- If the misfire rate may lead to permanent damage to the TWC, the Check Engine MIL flashes. If the misfire rate is no longer reached during the first journey, the MIL goes out. If the rate is reached during the next journey, the MIL flashes. If this misfire rate is subsequently no longer reached, the MIL changes to a continuous light.
NOTE:
- When using a block heater (for heating coolant), start and driving off difficulties or misfiring can occur if the block heater was connected for less than 4 hours.
- When the fuel tank is driven to empty, misfiring can occur. For this reason the fuel level in the tank is also stored in the memory when misfiring occurs. If the tank was nearly empty, there was probably no fault. Erase fault memory and road test vehicle.
- In the event of a short circuit to B+ or ground in the oxygen sensors ahead of the TWC, the mixture becomes too lean or too rich. This can cause misfiring. If, in addition, an oxygen sensor signal fault ahead of the TWC is stored in memory, first correct this fault and then road test the vehicle.
Possible fault cause
- Fault in ignition system
- Fault in injection system
- Flat-base tappets (valve lift fault)
- Mixture too rich
- Mixture too lean
- Mechanical causes:
Valve lifter chattering
This is caused by dirt in the valve lifter.
When the Check Engine MIL lights up, a chattering valve lifter may also occur for a certain time. The DME control module registers (sporadic) misfiring at one or more cylinders. The mixture adaptation values are normal.
Remedy:
1 - Remove lifter bores, check for damage and blow out oil passages.
2 - Replace all valve lifters.
3 - During the test drive, listen for valve lifter noises.
Camshaft control times adjusted
The camshaft control times have changed. No chattering noises occur. The DME control module indicates misfiring for the entire cylinder bank 1 or 2. The mixture adaptation values in the idle speed range differ in bank 1 and bank 2, the mixture adaptation values in the upper and lower load ranges are generally normal.
Remedy:
1 - Carry out raw emission measurement:
1. Reset mixture adaptation values (disconnect battery)
2. Disconnect oxygen sensors
If the difference between bank 1 and bank 2 is greater than approx. 0.8 %, then
1 - Set the camshaft control times again.
2 - Road test vehicle. The mixture adaptation values must be normal.
VarioCam does not switch over completely
The VarioCam does not switch over completely from power to torque valve timing.
An indication of this problem is misfiring detected by the DME control module in the range of 1200 - 1500 rpm occurring in an entire bank.
The mixture adaptation values are normal.
Remedy:
1 - Replace VarioCam.
2 - Road test vehicle.
Other possible fault causes
- worn camshafts
- leaking valves
- faulty piston rings
If opposing cylinders have misfiring, the cause could be the sensor wheel.
If valve lift faults are suspected, perform the system test for large lift and the system test for small lift with the Porsche System Tester 2.
NOTE: If the battery was disconnected, at least range 1 of sensor wheel adaptation must be adapted before troubleshooting is carried out; see actual values explanation.
Diagnosis/Troubleshooting
NOTE: If there is a lot of oil in the engine, check that the oil filler tube and cap are tight.
Part 1:
Part 2:
NOTE: The seal or sealing ring in the brass closure cap is not exchangeable. It must therefore be used only once.
Tightening torque of new brass closure cap 2.5 ± 0.5 Nm (2.0 ° 0.5 ftlb.)
Part 3:
NOTE: It is essential to observe safety regulations for handling fuel.
Part 4:
Figure:
WARNING: Tester cables must not be connected to ground.
NOTE: If the engine does not start, or if the idling speed drops, replace tester cable connected to special tool.
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 one valve on one cylinder is faulty.
In order to ensure that the fault is repaired, 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 sensors during acceleration with wide-open throttle or to record their behaviour with the data logger.
Continue by performing the system test for small lift
Perform system test for small lift
WARNING: Test is carried out while driving. Have a second person operate the Porsche System Tester 2.
During the system test for small lift, the valves remain at small 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 small lift, the fault type "below limit" is recorded.
Several cylinders may be stored as faulty, although only one valve on one cylinder is faulty.
In order to ensure that the fault is repaired, 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 enriches the mixture (F(R) > 1) during acceleration with wide-open throttle - see drawing below. Difference from the other oxygen sensor > approx. 15 %. In the case of a fault, the flat-base tappets of the inlet valves for the entire cylinder bank must be replaced.
1 - Select system test.
2 - Select "Request small lift".
If "Valve lift 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.
NOTE: If "Request small lift" appears, the valves remain at small lift, i.e. the performance is reduced dramatically.
4 - Perform acceleration with wide-open throttle in 2nd gear, until "Valve lift diagnosis completed" (max. 4,000 rpm) appears.
At speeds above 4,000 rpm, misfires may be stored. Delete the fault memory and repeat the test.
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 sensors during acceleration with wide-open throttle or to record their behaviour with the data logger.
End