Need an explanation on the CMP signal - help needed for algo

[spyghost]

i got this waveform from the service manual of a mitsubishi 4g18 engine (cedia lancer). the engine uses wasted spark. sensors are crank and cam with the following wave pattern

- The CKP sensor simply indicates that a pair of cylinders ar about to reach TDC (1/4 or 2/3). The CMP signal then signifies which injector to open and which coil pack to energize.
- The CMP leading edge is always 131 degrees BTDC - this indicates that one coil pack needs to be energized to fire up 1/4 - no doubt about it. These leading edge are 180-180 degrees apart.
- The CMP trailing edge signals what? - I don't get the logic behind having one vane at 90 degrees, and the other one at 45 degrees. These trailing edge are 135-225 degrees apart. Ideas why they are unequal?

If the function of the CMP signal is to merely indicate that coil packs for 1/4 needs to be energized, then what's the reason behind having one of the vanes half the size of the other? Is there something here that I am missing?

[Costa]

If the function of the CMP signal is to merely indicate that coil packs for 1/4 needs to be energized, then what's the reason behind having one of the vanes half the size of the other? Is there something here that I am missing?

It's to identify a complete cycle of the engine, for sequencial fuel injection.

The decoder for these is usually basic. The exact angle of the cam signal is not important.
-If the Cam signal falls when the crank position signal is high, cylinder 1 is in the first part of its cycle.
-If the cam signal falls when the crank position signal is low, cylinder 1 is in the second part of its cycle.

CA

[spyghost]

can the same set of signals be used for sequential spark?

[Costa]

Yes

[spyghost]

After some thinking and imagination, I got how the sequential spark and sequential injection will work. The falling edge of the CMP signal is only used during startups to determine the stroke of all other cylinders with respect to cylinder 1.

Based on the image I posted, the 4 pulses of the CKP signal above correspond to cylinders 1, 3, 4, and 2 on their compression stroke.

Having the CMP signal below (rotating half crank speed) and in direct relationship to cylinder 1, at initial startup:
- If the CKP signal is LOW, and the falling edge of the CMP signal appears, it means that the the next rising edge of the CKP signal should spark@3 and inject@2 (cylinder 3 at 75° BTDC compression, while cylinder 2 at 75° BTDC exhaust). Succeeding occurences of the CKP signal would follow the sequence: spark@4 and inject@1, spark@2 and inject@3, spark@1 and inject@4.
- If the CKP signal is HIGH, and a falling edge of the CMP signal appears, it means that the next rising edge of the CKP signal should spark@2, and inject@3 (cylinder 3 at 75° BTDC exhaust, while cylinder 2 2 at 75° BTDC compression). Succeeding occurences of the CKP signal would follow the sequence: spark@1 and inject@4, spark@3 and inject@2, spark@4 and inject@1.
- Any CKP signal without any falling CMP signal is ignored

After the initial startup and identification of the cylinder strokes, "the falling edge of CMP signal can be ignored entirely during the entire life of the engine running" (i might be wrong in this statement??? - verification???). On the other hand, the rising edge of the CMP signal can be used to identify engine RPM, since they are separated at exactly 180°.