Driveability Issues/ PROM Programming & Chassis Dyno
1990 Corvette Auto 383 TPI
Engine running rich, detonating. Customer running E85 with small amount of race gas mixed. Test drive, data scan, check fuel pressure and EFI sensors. Fuel pressure at 60 PSI & found oxygen sensor not working. Adjusted base fuel pressure to 45 PSI & replaced oxygen sensor. System will no go into closed loop. Checked base timing and found correct at 6 degrees. Test drove and reprogrammed PROM as needed to decrease/eliminate detonation. Fuel trims within range now, all sensors working. Ran vehicle on chassis dyno to check heavy load/WOT fuel mixture and detonation. Minimal detonation present, fuel mixture very rich. Made changes to lean fuel mixture but engine misfires due to insufficient ignition timing (18-20 deg) to prevent detonation. Engine needs lower compression ratio. Suggest 9.5:1 compression.