tici

iTrader: (1)

Is that something you guys change according to the injector type?
Or to achieve a particular goal?

I don't have a particular need, I'd just like to learn more about that

thanks

Stefano

SSpdDmon

iTrader: (10)

Values in this table should be based on injector performance. They basically get added to the calculated pulse width (based on VE, MAF, IFR, etc.). This is some effect from this table on fueling. But, it becomes more and more minimal as injector pulsewidths increase (like at WOT). Primarily, this is changed after a big injector swap to get pulse widths in a respectable range for decel and idle.

tici

iTrader: (1)

I have now #36 Bosch injectors instead of the original #28. Stock fuel pump.
Everything seems to be tuned properly (IFR, MAF, VE), the fuel trims are very close to zero.

I changed the offset once +10% and once -10% to seen if there is a difference: with +10% the fuel trims decrease about 1.5%, with -10% increase by the same percentage (logically).

With +10% the car feels stronger and has a faster respond to throttle changes than with the stock settings. This for the low and middle power range. WOT is the same.

Theoretically the injectors are the same: both Bosch, both the same shape. I guess only the internal holes are different (?)
Do you see a reason for the changed behaviour when the injectors are turned on a little sooner?

SSpdDmon

iTrader: (10)

The bigger injectors might naturally take a little longer to open/close. So, a 10% increase may be needed over the stock settings. Ideally, injector performance should be available from the manufacturer as it is dependant on voltage....not necessarily application. Try searching the net and see what you can come up with. I know you can find offsets for Motron 60's, SVO 30's, etc. Maybe there's something someone posted for what you have???

2002_Z28_Six_Speed

iTrader: (19)

Bigger, low impedance injectors should in theory have more trouble keeping a field under low voltage conditions.

I could imagine making a setup to test this but you would have to pull the alternator and battery and have a variable dc power supply big enough to run the whole car.

Your local college/high school lab isn't gonna cut it...

cosmo vyss

I have gone from stock injectors to FAST36LBS ones and have only changed the flow rates.

I may try this pulse offset as I have been having some leaning out issues at part throttle when cruising. The car doesn't like having DFCO on and lean cruise is just not happening.


JB

tici

iTrader: (1)

Well, the PCM will adjust the injectors opening time according to the O2's signals. Tuning the IFR will bring back fuel trims where they are supposed to be too.

What I really don' tknow is the effect of spraying fuel sooner or later.
There is for sure an optimal moment: for a stock engine it's what is programmed in the PCM. But how to determinate this moment with different injectors?

What to scan? What is the goal?

SSpdDmon

iTrader: (10)

I don't know if you can do this by scanning the sensors available on the car. IMO - it's related to injector performance as measured in a lab with some heavy duty timing and pressure equipment. That is why I recommended looking for manufacturer specs on the injectors you purchased.

This table basically represents the amount of time it takes for the injector to open/close based on the voltage and manifold vacuum present. The best thing you would have to go on is maybe 1/4 mile, dyno, or butt dyno performance. The downside to avoid is opening your injectors too soon and ending up with some fuel puddling. Personally, I think a 20~30% change over stock would be the max I'd be willing to test to assuming the injector is slower, which it most likely is.

Reject

iTrader: (24)

do you happen to have the correct offset table on hand?

SSpdDmon

iTrader: (10)

www.google.com

That's about the best I can offer...

tici

iTrader: (1)

Guys: we all know Google, we all know how to change those values and we all know what those values mean.

But.... how to find them out???
I'm sure it's not a matter of try and error.

Is that a value that only depends on the injectors or on the PCM (speed for example) or on the cam (intake valve timing, cam profile?)

SSpdDmon

iTrader: (10)

...
Again, it's injector performance based on voltage and pressure.