MicroSquirt.com read only forum (Jan.15,2018)

Does anybody know what exactly is happening with injection delay?

I understand its a percentage of degrees. I assume uS gets the 100% value from the number of cylinders set in injection control set up. My set up being a vtwin or 2 cyl would be 360* or would it be 720*?

Is tach pulse reference point uS sets for injection fom the actual crank sensor signal point or is it the point calculated by crank sensor, delay teeth and trigger offset? (which should be tdc)

With an injection delay setting of 0, Where exactly is that in reguards to crank position when injector pulse occurs? (how many degrees after tach)

I assume the delay is used for both cylinder injectors, #2 being calculated from offset setting. Both injector pulses would be timed and delayed the same relative to there own piston/ intake stroke. So in theory, the math or operation used for a single cylinder is the same as just looking at #1 cylinder from a twin? Right?

I will Al chime in here but I think you have a handle on the timing. Everything is linked to the "tach pulse" which is driven by the trigger offset, etc. The injector delay value just delays from when the tach pulse occurs.

- Bruce

yes, i got it now. I will answer my questions for future reader interest.

-360*

-tach point is -calculated point from crank senor + delay teeth. (trigger offset not used)

-setting of 0 is exactly at tach pulse (calculated point)

-no, the ignition offset is only for ignition. The uS always assumes (and uses) even fire for fuel. Odd fire engines will have #2 injection more advanced/ closer to tdc intake. (by same degrees as your ignition offset) as compared to #1.

800vtwin wrote:

I understand its a percentage of degrees. I assume uS gets the 100% value from the number of cylinders set in injection control set up. My set up being a vtwin or 2 cyl would be 360* or would it be 720*?

>>> For 2 cyl sequential you fire 2x per 720 deg, so a tach pulse every 360 deg; For wasted it would be every 180 deg. This is specified to the ECU by the No_Skip_Teeth input.

Is tach pulse reference point uS sets for injection fom the actual crank sensor signal point or is it the point calculated by crank sensor, delay teeth and trigger offset? (which should be tdc)

>>>> The first tach pulse arrives a tooth # 1 + Delay_Teeth after. Tooth no. 1 is the first tooth after the missing gap. The next tach pulses arrive every Skip_Teeth after that. Where is TDC relative to teh tach pulse? It is defined by Trigger Offset. I am assuming you are using Dual Spark Mode and so trigger offset should be 0 or negative. If it is say -60 deg, this means the tach pulse arrived 60 deg after TDC.

With an injection delay setting of 0, Where exactly is that in reguards to crank position when injector pulse occurs? (how many degrees after tach)

>>>>> InjStartTime specifies when the injection occurs relative to the tach pulse. If it is 0%, the injection is immediately after the tach pulse (or at least as fast as the processor can get to it). If it is 30%, it occurs 30% x no. crank degrees between tach pulses after the tach pulse, but is forced to inject by 2 ms before the next tach. This is because if the processor doesn't get to it fast enough, that is before the next tach pulse comes in, it will miss the injection and that would be bad. The only time this limitation wil come into play is at higher rpms and you won't know the difference because injector timing doesn't have a big effect at high rpm.

I assume the delay is used for both cylinder injectors, #2 being calculated from offset setting. Both injector pulses would be timed and delayed the same relative to there own piston/ intake stroke. So in theory, the math or operation used for a single cylinder is the same as just looking at #1 cylinder from a twin? Right?

>>> You are correct for an even fire engine, but I didn't think about odd-fire engines when I added the InjStartTime logic. Someone pointed that out a while ago. So with the present code, the injection is still referenced to the tach pulse and does not factor in the Odd angle offset which is just added in as an extra advance/ retrard of the spark timing, but doesn't affect the injection timing. I have since fixed this, but haven't gotten around to releasing it. The fix is in Sequencer code, which is also back-compatible with microsquirt and MS2. I am in the process of documenting this for the Megameet in Seattle in October and I am working with someone who wants to test it. I should have the documentation finished by the coming week and will release the code as soon as I get confirmation that it works on a real engine. I tested it more thoroughly on the bench this weekend and it works even for an 8 cylinder, but it has to be set up for a negative odd angle offset, so the cylinders may have to be swapped to achieve this.