Misfire. P0300,0301,0302,0303

[hmhaga]

1998 Boxster 2.5. Mileage ~100.000

The engine misfires when cruising and on high loads/rpms. It has been like this for a while, but yesterday it finally triggered the CEL. A permanent light at first, but it started flashing after a while

I borrowed an OBD scanner and read the following codes:

P0300 - Engine misfire

P0301 - Cyl 1 misfire

P0302 - Cyl 2 misfire

P0303 - Cyl 3 misfire

I cleared the codes, but it is still misfiring and hesitates slightly on idle. Any typical faults causing these codes? I've read the other threads and came up with: Variocam solenoid, AOS malfunction, Air leak. As the fault is present at only one cylinder bank, bad spark plugs is not the explanation?

This is the diagnosis report from ProScan: http://home.c2i.net/hmhaga/boxster/diagnosis.pdf

Any chance that more codes are stored, hidden from the OBD-interface?

Bummer....just had the car removed from winter storage :(

[Loren]

Yes, there is a good chance there are more codes (not hidden - just more).

If you notice all of you problem are on one side (bank) if the engine.

This could be a an intake air leak on that side or bad adjusted camshaft control for that side.

If the it is a badly adjusted camshaft control then the adaptation values in area 1 differ in bank 1 and bank 2 (e.g. TRA=0.02/TRA2=0.27). The adaptation values for area 2 are generally normal.

If this is the case the camshaft control needs to be reset - then recheck the adaption values.

P0300 Misfire Damaging to Catalytic Converter

P0301 Misfire, Cylinder 1, Damaging to Catalytic Converter

P0302 Misfire, Cylinder 2, Damaging to Catalytic Converter

P0303 Misfire, Cylinder 3, Damaging to Catalytic Converter

[CJ_Boxster]

same thing happened to me, Turns out it was the o2 Sensor ahead of the cats that caused the misfire on that same bank of the engine

My Pcodes were P0304, P0305, P0306 (cylindars 4, 5 & 6, Bank 2) & P0300 (Multiple Misfire) and 1 DTC which is a pcode that registered during my drive which was P0150 (Non-Functioning o2 Sensor Bank 2 ahead of cats)

Installed the new o2 Sensor and Check Engine light stopped flashing and fuel efficency went up and idle was smoother.

The o2 Sensor is usually what causes misfires on only one bank all at once because it's pretty much the only sensor that will detect output from only 1 half or 1 bank of the engine, Any other part malfuntioning and causing misfire on all cylindars in 1 bank would be purely coincidental.

[hmhaga]

Thanks Loren. The CEL/misfire only appeared after having passed 5500 rpm.

After resetting the CEL and some "spirited" driving the problem hasn't reappeared. HOWEVER, it has regained response and torque I can't remember it ever having in my ownership....