So you’ve finally got your RB swap in place and ready to start, but your RB25 won’t start. After a bit of troubleshooting you discover that your RB25 engine swap doesn’t have spark or your injectors aren’t firing. One of the leading causes for your RB25 swap not starting is the RB25 crank sensor. This part is also known as the crank angle sensor, and it’s a four wire sensor that’s mounted to your intake camshaft.
While many crank angle sensors are mounted to the crank or to the oil pump to read a crank trigger plate, the Nissan RB25 crank sensor is also known as the cam sensor. Today I’ll be showing you how to test the RB25 crank sensor in a 1998 Nissan Skyline GTS-T. This RB25DET won’t start because of a faulty crank sensor, and using a digital multimeter I’ll be showing you how to test it.
Because the RB25 crank sensor is directly mounted to the intake camshaft, measuring and testing it is very different.
The four wires to this sensor are comprised of a power and ground circuits, and a 1º to a 120º signal. Because of this you’ll be unplugging the crank sensor directly to measure the harness.
When you are testing the RB25 crank sensor, you will need to insert your ignition key and turn to the “ON” position to send power. We’ll begin by testing the power wire to your RB25 crank sensor. Problems with this sensor can lead to engine misfire at best, or your RB25 wont start at worst.
Checking your RB25 crank sensor for power
The two wires of your harness you will be checking are the furthest two on the right when looking at the back of the plug. Refer to the RB25 crank sensor wiring harness wiring diagram below to reference PIN 3 and PIN 4. PIN 3 is the power circuit, which runs to your RB25 ECCS Relay.
This wire tees into your RB25 main relay and powers the engine computer at terminals 49 and 59. Using your multimeter, put the black lead on a engine ground and gently probe the front of PIN 3 for power. Make sure that your ignition is turned to the ON position. If you have switched power here, the next wire to check is the ground circuit.
Place the red lead of the digital multimeter on the positive battery terminal and then probe PIN 4 of the RB25 crank sensor for ground. This wire runs to the RB25 ECU and terminates at PIN 50.
If your RB25 crank sensor has power and ground, it has what it needs to operate. The next two wires you will be checking are the crank signal wires. Luckily for you testing this part of your RB25 cam sensor / crank angle sensor is easy to do.
Remove the bolts that secure the RB25 cam sensor in place. Slide out the cam sensor carefully and then you can begin testing the signal wires. If you have a RB25 swap in a Nissan 240SX, you may need to remove the radiator for clearance.
Now plug the RB25 crank sensor back in, and you will be piercing the wire at PIN 1 and PIN 2.
With the ignition turned to the ON position, you will be measuring for voltage here while spinning the shaft of your RB25 cam sensor.
Testing either one of these wires is the same procedure. You will be rotating your RB25 CAS until you see voltage spike at PIN 1 and PIN 2. Because the signal is for PIN 1 and PIN 2 at 120 degrees of phase, you will see the spiking current with regularity.
If your RB25 cam sensor reacts in the sufficient manner, chances are it’s still good and your misfire issue lies elsewhere. If you have noid lights, install them now to check for fuel injection pulse with the cas removed. If you have spark and fuel with the RB25 crank sensor removed, there’s a problem with your camshaft. When problems with your RB25 misfire continue to linger, make sure to check these guides below to test your ignition.
Once you’ve tested your RB25 cam sensor and found it bad, replace it with a new unit to get your Skyline or RB25 swap back on the road. After you are done however you will need to set your RB25 engine idle and ignition timing.
Setting your RB25 ignition timing
Warm up your RB25 swap and once it’s warm make sure that your idle is properly set. Unplug your idle switch which is the bottom wire on your RB25 throttle position sensor. Connect your timing light to your battery and the signal clamp onto the number 1 spark plug of your RB25DET.
Aim the timing light downward at your RB25 engine cover, near your crankshaft.
You should see a fixed mark that looks like an iron sight to a gun. This will line up the marks on your crankshaft pulley everytime your timing light goes off.
The RB25 crankshaft will have 7 marks, which signify the degrees from 0 to 30º. Each mark on the crankshaft signifies 5 degrees of base timing, and the 0 mark is orange or sometimes red.
Have any questions about our guide to testing your RB25 Crank Sensor? Leave us a comment below and let us know!
