Here's one that has me stumped, my 87 GN went from running great to crappy in one day. I have recently installed a TH downpipe and Tomka Cold air and was getting around 15 to 18 psi with some knock at full boost. The car has Thrasher chip and blue tops, 43TS plugs gapped to 35. I turned down the boost to keep it under 15 using the adj wastegate, hoping to get rid of the knock. After taking the car out for a sunday drive the knock is worse, as soon as the boost gets to 10 there is heavy audible knock and the red lights on the knock gauge lite up. If I keep it under 10 it seems to accel ok. Here is what I have done to try to find the problem. Replaced the blue tops and injector harness with known good stock parts, installed Thrasher chip for stock inj, replaced coil pack and module with one from known good car, installed maf from same car, substituted ecm from same car. Same problem no change. I checked the crank and cam sensor waveform with a labscope while driving, no dropouts waveform looks normal. It knocks so loudly that I am afraid I will do some damage to the motor if it continues. I am thinking timing chain or maybe broken valve spring? does this sound right to any of you. I am starting to get discouraged, don't know what to check next.