94 GS-R V-TEC problems

To anyone who cam HELP!!! My best friend has a 94 gs-r integra with some v-tech problems.. At high rpm v-tec isn't kicking in. I've checked everything from the silenoid switch to replacing the oil pressure switch. Nothing is working! I've pulled the silenoid apart and checked the filter, made sure the plunger is moving freely, and so on. I'm at a lose with this thing. But beyond all this the car is running great. I believe it's internal. I was thinking that the mid-rockers are having issues. But I'm not sure because I having taken it down that far yet. If anyone has any ideas please feel free to let me know. Thanks!

hi check the engines oil pressure at high revs and do a air pressure test on the heads valve to see if it opens and hold the pressure at 57psi paul