NISSAN VG30DE(TT) CAM ANGLE SENSOR COUPLING MISALIGNMENT CAN CAUSE UNEXPLAINED DETONATION IN HIGH PERFORMANCE ENGINES
Nissan’s VG30DE(TT) for the most part is a well-designed engine compared to others designed in the eighties. Like all engines, it to has a few warts, one of which is the topic of discussion here, but first a little back ground. Nissan had chose to use a self-enclosed dual channel optic sensor to track the rotational position of the engine on the VG30DE. The Camshaft Angle Sensor (CAS) is coupled to the front of the left exhaust camshaft via a splined coupling pin pressed into the front of the camshaft. As it is necessary to have a sensor that can accurately report the engine’s rotational position throughout a full 720 crank degrees, attaching it to the first camshaft being pulled by the timing belt was the most accurate choice. In theory this was a good layout, but in production, caused Nissan a bit of grief. Almost as soon as the Z32 was released in 1989, the CAS coupling pins started wearing at an alarming rate. A technical service bulletin was issued when it was discovered that the cause was a slight eccentricity in the alignment of the CAS to the camshaft, caused by a machining error of the CAS mounting bracket to cylinder head aligning dowel holes. This would cause the coupling splines to wear, causing a large amount of backlash at the CAS, which in turn sent an erratic position signal to the ECU. The backlash can wear to as much as 3 or 4 cam degrees, causing the ignition timing to wander as much as 6 to 8 crankshaft degrees! This condition can cause unexplained detonation in various RPM ranges, as the CAS resonated from the backlash. Nissan’s bulletin also stated that the cylinder head must be replaced if the CAS mount was not concentric to the cam-bearing bore. While this Service Bulletin was specific to early production of the 1990 model, it is not uncommon to find unacceptable misalignment in later engines for various reasons.