for starters is swap in known good parts. Start with the PTU and then the CAS. If the CAS is found to be bad check out my writeup in the FAQ on cleaning it. There are different types of CAS but the procedure is basically the same. The CAS controls when the injectors spray and when the coil packs fire. If no change check connections, spark plug, ECU and lastly harness continuity. That should pretty much eliminate the electronics. If all that checks out it may be a mechanical problem, low compression, dirty valves ect. Or the injector(s) may not be working properly.
