Quick question for you guys. I need to confirm that a CAS on an SR rotates at half the speed of the cam gear that spins it. It is totally logical that it would but I need to be sure. In other words, the CAS rotates at the same rate as the crank, correct?
Secondly, the CAS has 4 pins, power, signal, signal and ground. How does the CAS output its position through these 2 signal wires?
Thanks in advance guys!
SR CAS Question
-
Seishuku
- Posts: 498
- Joined: Fri May 13, 2005 6:19 pm
- Car: 1987 Nissan S12, 5-speed, SR20DE+T 50trim T3@15PSI, Megasquirt 1 029y4
Re: SR CAS Question
The CAS rotates at cam speed.
It has a disc with two sets of slots, the inner slots depend on how many cylinders you have (in this case, 4) and are each different length, there are 360 outer slots. What the ECU does, is when it detects the rising edge of the inner slot, it starts counting how many outer slots pass until it picks up the falling edge of the inner slot. From that it can tell exactly which cylinder it's on.
That's how the Nissan CAS works on coil-on-plug systems, the distributor systems work the same way, only difference is that it can only detect where cylinder one is at (since it doesn't care about the others, it only needs TDC).
Also, the rising edge of the inner slots are all in the same location, the falling edge depends on the length of the slot obviously.
It's also an open collector sensor, meaning the signal output is actually the collector of the transistor in the sensor, when the sensor is triggered, the signal lead is grounded.
It's a square wave signal.
It has a disc with two sets of slots, the inner slots depend on how many cylinders you have (in this case, 4) and are each different length, there are 360 outer slots. What the ECU does, is when it detects the rising edge of the inner slot, it starts counting how many outer slots pass until it picks up the falling edge of the inner slot. From that it can tell exactly which cylinder it's on.
That's how the Nissan CAS works on coil-on-plug systems, the distributor systems work the same way, only difference is that it can only detect where cylinder one is at (since it doesn't care about the others, it only needs TDC).
Also, the rising edge of the inner slots are all in the same location, the falling edge depends on the length of the slot obviously.
It's also an open collector sensor, meaning the signal output is actually the collector of the transistor in the sensor, when the sensor is triggered, the signal lead is grounded.
It's a square wave signal.
Re: SR CAS Question
Makes sense. So that brings be to the question are the slotted waffer kinda discs the same or different between a KA24E and an SR20DET?
From both FMS's it would appear they are, correct? And thus they would be interchangeable parts if they had the same input shafts, right (I'm speaking in terms of function)?
From both FMS's it would appear they are, correct? And thus they would be interchangeable parts if they had the same input shafts, right (I'm speaking in terms of function)?
-
Seishuku
- Posts: 498
- Joined: Fri May 13, 2005 6:19 pm
- Car: 1987 Nissan S12, 5-speed, SR20DE+T 50trim T3@15PSI, Megasquirt 1 029y4
Re: SR CAS Question
The discs have the same dimensions, but the KA has a distributor, so it has 3 equal length inner slots and one long one... Which means the ECU can't tell which exact cylinder it's on, other than cylinder one.
The only CAS disc you would be able to use, is one from another Nissan 4 cylinder coil-on-plug engine... Which would be any SR20DET, FWD or RWD (different CAS body, but discs and sensor modules are the same).
The only CAS disc you would be able to use, is one from another Nissan 4 cylinder coil-on-plug engine... Which would be any SR20DET, FWD or RWD (different CAS body, but discs and sensor modules are the same).