My 1995 R33 Gtr sometime's has a missfire for a split second and then it's fine again, It mainly happens at 2500 - 3000 RPM just before boost kicks in. I took it to a workshop and they said change the coilpacks and spark plugs so I did to Splitfire's and to Copper spark plugs but it still happens they also check for boost leaks and they found nothing wrong. I have checked the earth cable's they are fine too. At 2500 - 2800 ign timing sit's around 38 degs. Any Suggestions on what could be causing this?
Fuel Type: 100 oct
Boost Pressure: 7 Psi
Turbos: Garrett 2860's smallest in that serie
Spark plug Gap: 0.8
Spark plug type: Copper
ECU: Apexi Power FC
Max Knock Reading: 109 only happened twice, But normaly is around 3 to 10
Battery Volts: 14.2
Max ign timing reading: 42 deg