Vtc And Injector Timing

[frozenwaffles]

So what tells the injectors to fire? I know the ecu does but whats it linked to?

Does vtc cause them to fire 20deg earlier?

[TiTAN]

VCT has nothing do to with injector timing, VCT advances/retards the cam timing so the valves open/close earler/later

[frozenwaffles]

Correct me if im wrong, but isnt injector timing and valve opening timing critical to be synced together...

Ie when the valve is opening the injector fires so the air rushing in takes with it the atomised fuel?

[JonnoHR31]

its all controlled by the ecu. why do you ask?

[frozenwaffles]

did you even read my first post???

the reason i ask is that from my reading so far, and sheer logic, its important for the injector to fire at a certain time in relation to the valve opening (working out if this is before the valve opens or after or during or whatever). based on this knowledge, if you take into account VTC and the advancement of the cam shaft by 20deg, does the ecu then add 20deg timing to the injector pulses?

further to this again, if i remove VCT or atleast just disconnect it, will the ECU still be firing as if the VTC was working (one would assume so)? and then just by telling the PowerFC to have the VTC point at 1050rpm (rather than 4700rpm which is where it would normally turn VTC advancement off (so in effect not activating it at all), will this assit with fuel delivery, emission and economy?

[blind_elk]

The injectors are timed by the CAS. Because the CAS is the only sensor that knows where TDC is, and where each individual degree of crank rotation is.

I'm guessing that if the ECU has switched on VCT, then the ECU knows to alter the injector firing time to suit.

[JonnoHR31]

did you even read my first post???

the reason i ask is that from my reading so far, and sheer logic, its important for the injector to fire at a certain time in relation to the valve opening (working out if this is before the valve opens or after or during or whatever). based on this knowledge, if you take into account VTC and the advancement of the cam shaft by 20deg, does the ecu then add 20deg timing to the injector pulses?

further to this again, if i remove VCT or atleast just disconnect it, will the ECU still be firing as if the VTC was working (one would assume so)? and then just by telling the PowerFC to have the VTC point at 1050rpm (rather than 4700rpm which is where it would normally turn VTC advancement off (so in effect not activating it at all), will this assit with fuel delivery, emission and economy?

not sure if the ecu changes the injector timing but even if it does it'd only do so whilst vct is active, as the switch points vary depending on load. so if you disable it through the ecu (if the power fc lets you set it low enough) then it wont be a problem

[Dose Pipe Sutututu]

this is how I believe it works, I could put it in visio if anyone wants me to (I could be totally wrong to)

CAS --> ECU <--> VTC Activation Point <--> ECU --> Injectors

When the VTC advances it's 10degrees, the injectors would fire corresponding to the CAS + the VTC for those rev ranges.

If it doesn't, you'll be supplying delayed fuel into the motor.

So frozenwaffles if you decide to D/C your VTC, you should set the kick off point for VTC at 0rpm in Datalogit, this will always keep the VTC off and allow for the injectors to kick off at the right time rather than disconnecting the solenoid because the ECU still thinks VTC is running and advances the injection pulse to compensate for valves opening earlier.

Liek I said, I could be wrong abotu this

[frozenwaffles]

John, thanks that all makes a lot of sense.

just so you know, the VTC advances by 20deg, not 10.

also i tried setting the POwer FC VTC setting to 0rpm in datalogit and that made it seem to turn on and off with accelerator activity...very strange. i have since set it to 1050 rpm which is its normal switch on point and its all good no, its not activating at all...

i have reset my HKS cams to their 0deg points and i'll see how it all goes from here...

[frozenwaffles]

also is there any way in datalogic to see the injector timing in relation to spark timing? and rpm?

[rob82]

also is there any way in datalogic to see the injector timing in relation to spark timing? and rpm?

I dont think the injection phase angle is available in the datalogit software from memory although I dont have the software in front of me.

Usually the injection phase angle isn't that critical and most times you will not even notice a change in fuelling with +/-30 deg phase movement from the optimal injection angle even at the most critical rpm point. Once you start loosing nice injector spray patterns and decresed combustion efficiency with less dynamic engines the optimal phase angles can be within +/-100degs. So worrying about 20deg VCT injection phase adjustment is pointless IMO.

[STATUS]

i pretty sure there is no compensation in the pfc for VTC angle change. Even with an ecu that does i doubt there is a accurate enough way of yielding quantifiable results ( vtc minimal 20 deg change) with the engine setup you have.

Various ecu's have a nice table for playing with injection timing (usually in degrees), it is most handy for cold starting, idle (especially on big cammed engines) and cruise mixtures but less important as the revs increase.

[STATUS]

John, thanks that all makes a lot of sense.

just so you know, the VTC advances by 20deg, not 10.

also i tried setting the POwer FC VTC setting to 0rpm in datalogit and that made it seem to turn on and off with accelerator activity...very strange. i have since set it to 1050 rpm which is its normal switch on point and its all good no, its not activating at all...

i have reset my HKS cams to their 0deg points and i'll see how it all goes from here...

that makes perfect sense, as you can only adjust the OFF point.

VTC on @ 1050 (approx) and off @ user determined rpm (setting in PFC).... usually 4700.

[VB-]

dont think injector timing is that critical, just look at the number of ECU's that run batch fire...

[scotty nm35]

I would have thought the best time to fire would be only when the valves are open, wouldn't you get pooling otherwise? Mind you I was running 97% duty on my injectors until I upgraded last week.

Larger injectors would allow you to stay within this window wouldn't they?