Skyline GT-R sensor upgrade: modern sensors and ECU failsafes

The short answer

A wideband O2 sensor reads the full rich-to-lean range, not just around lambda 1.
Oil and fuel pressure sensors let the ECU warn you, cut power or limit revs when pressure drops.
A flex fuel sensor reads ethanol content and fuel temperature so the tune can adjust for the blend.
Modern ECUs can act on sensor readings and sensor faults, not just log them.

What the factory setup measures

Haltech lists the factory connections its plug-and-play harness supports on the R32, R33 and R34 GT-R. They include the front and rear AFMs, front and rear O2 sensors, knock sensors 1 and 2, the coolant and air temperature sensors, the throttle position sensor and the vehicle speed sensor. MoTeC describes the RB26 as using a 360 degree optical trigger on the camshaft. That list doesn't include fuel pressure, ethanol content or exhaust gas temperature sensors. Those are added when a build needs them.

AFM or MAP

The factory ECU measures airflow through the AFMs. Modern ECUs can use the AFMs or manifold pressure instead. Haltech's plug-in harness supports the front and rear AFMs. Link's NGTRX plug-in ECU has a built-in MAP sensor. MoTeC's GPR software models engine load from inlet manifold pressure and inlet manifold temperature. Which one suits your car depends on your intake, turbos and tune, so ask your tuner.

Wideband O2 sensors

Bosch says its switching-type (jump) O2 sensors read lambda 0.93 to 1.15. Its LSU 4.9 wideband sensor reads from lambda 0.65 to open air, works with petrol, diesel and E85, and needs a dedicated controller to run it. The Haltech Nexus has onboard wideband control for LSU 4.9 or NTK sensors. MoTeC runs Bosch LSU 4.9 sensors through its LTC or NTK sensors through its LTCN. Link's ECUs can use a CAN wideband to watch the mixture and trigger a fail-safe if it goes lean.

Oil and fuel pressure sensors

Haltech says a fuel pressure sensor is used for datalogging, injector pressure differential tuning and engine protection. The Nexus auxiliary connector adds oil pressure monitoring and fuel pressure sensing. Link lets you set the minimum safe oil pressure as a table against RPM, load or temperature. If pressure drops below it, the ECU can warn the driver, apply soft or hard cuts, or shut down the engine. Link's fuel model can also compensate for fuel pressure.

Oil and fuel temperature sensors

Link says its ECUs track available sensor data, from coolant and oil temperature to intake air temperature, and can respond when a reading goes past your limits. MoTeC's GPR software lists inputs for engine oil pressure and temperature, and fuel pressure and temperature.

Flex fuel sensors

Haltech says its flex fuel composition sensor measures ethanol content and fuel temperature, so ECUs that support flex fuel can adjust the tune in real time for the blend. Haltech advises mounting it as close to the injectors as possible, ideally in the high-pressure feed to the fuel rail. Link lists flex fuel on the NGTRX, and MoTeC lists flex fuel operation in its GP software.

Knock sensing

The factory setup has two knock sensors. The Haltech Nexus lists dual knock control. Link says its knock system can detect the onset of knock and trim ignition timing, boost or fuel. MoTeC's GPR software has on-board knock control for each cylinder with up to four knock sensors.

Crank and cam triggers

The RB26 crank angle sensor sits on the cylinder head and is driven by the camshaft. MRE says its Twin Cam CAS Bracket holds the crank angle sensor on twin cam RB20, RB25 and RB26 heads and works with MRE trigger kits. If you change the trigger setup, check your ECU supports it. Link says that if a critical sensor such as the crankshaft position sensor fails, its ECU can switch to a reduced-power or limp mode so you can get somewhere safe.

Exhaust gas temperature (EGT)

Haltech offers per-cylinder shutdowns based on a maximum exhaust gas temperature. MoTeC reads EGT through its TCA thermocouple amplifier, generic CAN or E888.

Failsafes: what a modern ECU can do

Haltech's engine protection can put the engine into a safer state of tune, at up to three severity levels, when it detects an error or fault. You choose a protection level for each sensor. Haltech lists low oil pressure, low fuel pressure, excessive temperatures and lean AFR as common uses. The actions include enrichment, boost correction, ignition retard and a rev limit. For low oil pressure, Haltech recommends a low rev limit rather than shutting the engine down at speed, so you can pull over safely. Link offers enrichment, timing reduction, boost or torque reduction, fail-safe modes, hard or soft cuts, or shutdown. Link also points out that an ECU is only one part of keeping an engine safe, alongside good maintenance.

Which parts to look at

Engine protection depends on the ECU, the sensors fitted and how your tuner sets the limits. Plan sensors and ECU together, and ask your tuner which inputs your build needs.

FAQ

Why upgrade from the factory GT-R sensors?

The factory sensors were designed around the factory ECU. Modern sensors and ECUs add measurements and engine protection the factory setup doesn't include.

Do I need a wideband O2 sensor?

Bosch's LSU 4.9 wideband reads from lambda 0.65 to open air, while Bosch's switching-type sensors read lambda 0.93 to 1.15. Ask your tuner what your tune needs.

What can an ECU do if oil pressure drops?

Depending on the ECU and setup, it can warn you, cut power, limit revs or shut the engine down. Haltech recommends a low rev limit so you can pull over safely.

What does a flex fuel sensor measure?

Haltech says its flex fuel sensor measures ethanol content and fuel temperature, so a flex fuel ECU can adjust the tune for the blend.