I am running a C39 Hybrid Turbo with a Tial MVS external wastegate set up with a screamer pipe. We have been having trouble hitting boost, and so we got a boost leak test. Sure enough, Dv+ was leaking as well as slightly out the dump. We replaced with a new Dv+ and new wastegate diaphragm. After that we still were not hitting correct boost though, car was more responsive and such but still not peak. We have not gotten a new leak test since but AFR looks good, other than at times we run a bit rich hitting 11.02-10.88. We only get slightly lean at startup which I believe is normal (15.1) before it calms down to 14.55-14.7 at idle. Vacuum is at -10.1 to -9.88 at idle. During cruising vacuum is at -11 with no foot on the throttle. These numbers all seem relatively normal. We are hitting boost now, 24-25.5psi but with the WDGC maxed at 84%. I am starting to believe this might be a bad spark plug issue since vacuum looks fine and we are running rich at times (fuel not burning correctly I’d assume) and also seeing knock at times after a wide open pull and negative ignition correction on cylinders 1 and 4 ranging from -1.5 to -2.5 depending on the time it happens. My spark plugs are 1 step colder and have about 20k on them. I have new ones sitting in the garage that I’m going to throw on ASAP but want to know your opinions.
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