986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Engine Trouble. Would love some help. AOS?

thstone · 07-27-2014, 05:18 PM

This can often be a spark plug or coil issue.

Swap the coil packs from cyls 3 and 5 with the coil packs on the other side (4,6). Then see if you get a CEL for misfires on cyls 4 and 6. If so, replace those two coil packs. If the misfire stays with cyls 3 and 5, replace the spark plugs.

The reason that misfires are damaging to the cats is that when a misfire occurs, there is incomplete burning of the fuel and there is only so much fuel (or hydrocarbon) that a cat can take before it is permanently damaged. You should be fine running the engine to diagnose and repair the misfire but don't ignore the problem and continue to drive it while misfiring for a long period.

07-27-2014, 05:18 PM	#6
thstone Certified Boxster Addict Join Date: Nov 2010 Location: Los Angeles Posts: 7,669	This can often be a spark plug or coil issue. Swap the coil packs from cyls 3 and 5 with the coil packs on the other side (4,6). Then see if you get a CEL for misfires on cyls 4 and 6. If so, replace those two coil packs. If the misfire stays with cyls 3 and 5, replace the spark plugs. The reason that misfires are damaging to the cats is that when a misfire occurs, there is incomplete burning of the fuel and there is only so much fuel (or hydrocarbon) that a cat can take before it is permanently damaged. You should be fine running the engine to diagnose and repair the misfire but don't ignore the problem and continue to drive it while misfiring for a long period. __________________ 1999 996 C2 - sold - bought back - sold for more 1997 Spec Boxster BSR #254 1979 911 SC POC Licensed DE/TT Instructor Last edited by thstone; 07-27-2014 at 06:45 PM.