Cranking Algorithm

[powerboy]

Dear sir,

I would like to inquire about the details of the cranking algorithm. Initially, I set up a 24-2 crank and 1 cam sensor on a 2-cylinder engine.
Consequently, the missing teeth to 1 piston TDC is more than 180 degrees, and the cam pulse is BTDC (Before Top Dead Center) by 10 degrees. During the calibration process, using the cam pulsex1 and Trigger priority = 2, we found that 215 degrees is the match for 1# TDC.

Recently, in my attempt to learn more about the cranking algorithm, I turned off and unplugged the cam sensor. However, I forgot to change the ignition to wasted spark and the injector to multi-point group.
Surprisingly, the calibration showed 205 degrees as the match for 1# TDC with Trigger priority = 1. The engine ran as smoothly as it did with the cam sensor connected, and there was no increase in "Trig error counting."

I have a couple of questions:

Without the cam sensor, using only the 24-2 teeth on the crank wheel, direct spark, and sequential injection, is the accuracy of ECU acceptable?
Is there a special algorithm to track vacuum in the manifold while cranking?
Thank you for your assistance.

[Adamw]

All timing and engine control comes from the crank wheel.  The ecu uses the first crank tooth after the missing teeth as the index to reference where TDC is.  The cam sensor is only used to determine phase during startup - ie, is the next TDC exhaust stroke or compression stroke.  Once the engine has started the ecu can keep track of crank position and doesnt need the cam.   

If the cam sensor is disconnected/not working and fuel is set to sequential and/or ign is direct then it will only sync by "luck", approx 50% of start attempts it will sync on the wrong phase and wont start.  

 

9 hours ago, powerboy said:

Is there a special algorithm to track vacuum in the manifold while cranking?

Only in specific trigger modes in G4+.  G4X has a user configurable MAP level sync strategy.  Note however, if single throttle then MAP sync is only possible with 1 or 3 cyl engines or a 2 cylinder odd fire. With ITB throttles and the MAP sensor connected to one intake port you can do other engine types.  

[powerboy]

Thank a lot Adamw
I have another question

Why fuel trim cyl#2 is not working on  multi-point and wasted plug?

 

[Adamw]

Typically in multipoint group mode the injectors arent linked to a specific cylinder, all odd-numbered drives are fired together and all even-numbered drives are fired together.  A 2 cylinder engine is a bit of an exception where you could in theory do a trim in multipoint group but the firmware hasn't been designed to work like that.  You will need a trigger capable of 720 sync (cam sensor) and sequential injection to be able to make individual cyl adjustments.