During the development of the APS Intercooled Twin Turbo High Output System, a problem was encountered with the tuning of the engine. The problem manifested itself as ignition timing scatter under conditions that were intermittent, transient and at times occurred for only fractions of a second. In other words, the ignition timing would vary in a manner that was inconsistent with the engine RPM and engine load - and was not repeatable under identical operating conditions. In addition, due to the short period of time when the issue presented itself, very difficult to diagnose. The problem never the less did continue to appear on the APS engineering vehicle from time to time.
Tests were also conducted on a number of other 350 Z vehicles and whilst it was never encountered on those vehicles, the intermittent and erratic nature of the problem made it impossible to replicate without sustained long term testing of those vehicles. That is not to say that the problem does not occur on other vehicles, but it was an issue that did need addressing.
APS embarked on an exhaustive testing and engineering program to identify the cause of the problem and then deliver a solution that would be cost effective and practical.
After a great deal of data logging of the variety of sensor signals leading to the engine management computer, it was noticed that the signal quality from the crank angle sensor at times became erratic. The crank angle sensor is a vital component that informs the engine management computer of the exact position of the engine crankshaft and is used throughout the engine management program to control a variety of functions - in particular the ignition timing (when each spark plugs fires to ignite the air/fuel mixture inside the combustion chamber).
When the signal from the crank angle sensor becomes erratic, so does the ignition timing (in addition to other functions).
Ignition timing is a vital tuning parameter particularly in forced induction applications. If the ignition timing becomes retarded from the optimum point, the engine will produce less power and torque. However, and most alarming is when the ignition timing becomes advanced from the optimum point, pre-ignition and detonation may occur. Detonation places extremely high loads upon a variety of engine components such as pistons, conrods, bearings etc and the chance of failure of each or all of those components becomes very high.
With the intermittent and erratic behaviour of the crank angle sensor signal, either scenario was possible.
The engineering process continued at APS and the entire crank angle sensor circuit was painstakingly checked and verified using a variety of sophisticated electronic testing equipment. The circuit was found to be quite robust and electrically sound, however it did become susceptible to electromagnetic interference commonly found in a modern motor vehicle.
The solution was relatively simple (all the best solutions are!) and involved amongst other things, replacing the existing cabling from the crank angle sensor with robust shielded cable (and effectively earthed).
The entire crank angle sensor solution is included with each APS Intercooled Turbo system complete with factory connectors for a truly plug-in application.
After long term and demanding testing of the APS Intercooled Turbo system with the crank angle sensor solution installed, we are pleased to report that the timing scatter problems experienced with the APS engineering vehicle have never again occurred. Nor have they on any of the other 350Z vehicles APS has tested since.
A final point to consider is that the timing scatter problem was only ever encountered on the APS engineering vehicle. It may indeed have been a problem on that vehicle only when used with a forced induction system. The problem may not be present on other 350Z vehicles with other forced induction systems, be they turbocharged or supercharged, however due to the intermittent and transient nature of the problem, APS was not prepared to take the risk of assuming that it was a one-off occurrence - hence inclusion of the APS solution with all APS 350Z Intercooled Turbo Systems.