Fuel Injector Timing

[L31Sleeper]

Can the fuel injector timing be changed ?? I.E. on a sequential fire system can
the fuel be fired sooner or later.

Thanx
-Justin

[Aloicious]

unless I'm mistaken, B3702 is precisely that.

[Redline Motorsports]

Yes you can under the injector tab and it's based on coolant....at least with E38.. Dont have my laptop w me.

[L31Sleeper]

unless I'm mistaken, B3702 is precisely that.

I think you are correct, but it's based on coolant temp. I was thinking something
based on RPM so that maybe at high RPM you could advance it a little to keep up
with the intake valve opening ??.......just an idea.

Thanx
-Justin

[joecar]

It's not as simple as keeping up with the intake vale opening... at high RPM the injectors will be open for longer than the intake valve is open, there is no way to spray the whole load while the valve is open, the spray will hit the closed valve.

There is also wall wetting/evaporation effects which the PCM models since the spray hits the port walls and not just the valve.

[relentless addiction]

you have a great idea as i agree with your thinking... but being based on ect i dont see how this would be possible to be zero'd in on engine rpm... maybe someone will chime in to clear this up for us i have thought about this alot

[relentless addiction]

It's not as simple as keeping up with the intake vale opening... at high RPM the injectors will be open for longer than the intake valve is open, there is no way to spray the whole load while the valve is open, the spray will hit the closed valve.

There is also wall wetting/evaporation effects which the PCM models since the spray hits the port walls and not just the valve.

their is noway to start the injection event sooner?

[L31Sleeper]

It's not as simple as keeping up with the intake vale opening... at high RPM the injectors will be open for longer than the intake valve is open, there is no way to spray the whole load while the valve is open, the spray will hit the closed valve.

There is also wall wetting/evaporation effects which the PCM models since the spray hits the port walls and not just the valve.

Thank you Joe,
So basically you are building a puddle behind the valve that falls into the
cylinder when the valve opens, then I guess it really wouldn't matter.
So sequential fuel injection is really only useful at low speeds ?

Thanx
-Justin

[joecar]

The puddle has various characteristics... some of it will evaporate before the valve opens again, some of it will fall into the combustion chamber and evaporate there, and a few other modes;

also note that if for some reason the PCM can't figure out the crank/TDC phase on startup, it will fire the injectors in batch mode.

[swingtan]

Talking E38.....

{B1205} Injector timing vs. ECT
{B1206} Injector timing vs. RPM

And I believe that the timing in in degrees from TDC on the firing stroke.

As joecar says, the required injector pulse width will be longer than the inlet valve is open for and altering the timing will mess with fuel dynamics.

[L31Sleeper]

I thought it might be something useful to mess with, now that I have a little
more information I think I'll leave it alone.

Thanx
-Justin

[relentless addiction]

thank you for this useful info, e38 will be my builds pcm! much appreciated



Talking E38.....

{B1205} Injector timing vs. ECT
{B1206} Injector timing vs. RPM

And I believe that the timing in in degrees from TDC on the firing stroke.


As joecar says, the required injector pulse width will be longer than the inlet valve is open for and altering the timing will mess with fuel dynamics.

[joecar]

For example:

at 6000 rpm (100 rev/s), 1 complete cycle (2 revolutions 4 strokes) is 720° and takes 20.0 ms;

if the injector duty cycle was 80%, then the injector on time would be 16.0 ms (i.e. 80/100 * 20 ms);

if the cam's intake lobe had 240° duration, then the intake valve would be open for 6.67 ms (i.e. 240°/720° * 20 ms).

[Redline Motorsports]

I have had good luck by reducing the degrees by 20 on decent size cammed engines.. Much better idle stability and startup. Overlap can pull fuel and not use it so this seems to offset that effect.

[relentless addiction]

For example:

at 6000 rpm (100 rev/s), 1 complete cycle (2 revolutions 4 strokes) is 720° and takes 20.0 ms;

if the injector duty cycle was 80%, then the injector on time would be 16.0 ms (i.e. 80/100 * 20 ms);

if the cam's intake lobe had 240° duration, then the intake valve would be open for 6.67 ms (i.e. 240°/720° * 20 ms).




we need vvt or direct injection :)