SSpeedracer

iTrader: (8)

Did you change the idle RPM when you swaped cams? The "wisdom" you heard is more related to higher RPM operation, not low RPM.

Assuming that you kept the same RPM, the bigger cam probably has lower VE in which case fuel requirements are less. Conversely, if you raised the RPM, then fuel requirements would increase and might surpass those of the OEM setup. Your injectors would see a longer pulse width (PW).

Is it possible to change the injector Period (P) via the VCM? I doubt it, but if you can increase P, that will force the PW to increase also. I've got HPT but didnt look yet.

From your other post that <1.8ms commanded stalls out the car implies that the opening time (OT) is too long. This is both injector and driver related. In other words, OT on your car is different than OT on a different marque or model. In fact, OT will change, very slightly, from car to car accross the same model.

Supply/driver voltage will have a big effect of injector OT performance at low PW. The VCM contains look up tables to adjust PW based on voltage. A good high pressure fuel supply coupled with low system voltage will cause high impedance injectors to drop out at low RPM or fuel demands. The coil cant overcome the fuel pressure fast enough. Are all your accessories turned off? Good fresh battery? Alternator? Injector contacts clean? These might help you if your at the ragged edge power wise.

This is why low impedance injectors kick ***, you can control them better 'cause they're driven directly from the battery and arent current limited. However, the injector/driver setup costs more than most OEM's want to pay.

Every injector manufacture has SAE J1832 data available for every injector they sell. Up until the late 80's, all the injector manufactures were doing their own thing. OEM's couldn't compare injectors 'cause there was no standardization with which to measure. That all changed when the society of automotive engineers released J1832. It nails down everything imaginable, but data is from a test bench not a LS1 powered f-body.

No disrespect intended to Racetronix or any other speedshops, but the numbers sold aftermarket are barely a drop in the bucket and not worth the manufactures time. Furthermore, we would need the OEM SAE J1832 for the original injectors also, in order to compare. I would love to see all this data, but I'm not holding my breath. Please stop beating up Racetronix, you would be hardpressed to get better service from any other retailer or tier 1 supplier.

I am by no means an injector expert. In fact, I havent swapped injectors on my own LS1 yet. However, I am involved with low pressure gaseous injector design, most of which relates to low pressure gasoline fuel. My manager and director, both hold patents on injector design from the 80's and 90's while working for one of the big suppliers. I learn more each day.

WS6FirebirdTA00

iTrader: (33)

i dont think there is a period adjstmetn although there could be. idle with the injectors was increased to 900 to try and help out from 800, with the cam im idling at 800 right now.

i had everything off when i was doing this, the car when it woudl enter closed loop would stumble, mainly the proportional idle settings screwing with it. the battery is actually brand new and when the car is running im getting about 13v or so. how shoudl i try to mess with the voltage talbe. i woudlnt think i would have to mess with that.

thanks for the info sspeedracer, if you have anything else to add please let us know

SSpeedracer

iTrader: (8)

Dont mess with the voltage table, you need more information. I was just pointing out that OT and fuel flow rate varies with voltage.

Sounds like the proportional idle undershoot is putting your commanded fuel too low in the PW. What does the O2 mV look like at idle? Does it rail or clip at the bottom ~10mV?

Why did you return the idle back to 800rpm? If its hitting too low a PW at 800 RPM, try 900 rpm and see what the new minimum pulse width is. I gather that your car stumbles below 1.8ms. So, at what RPM does it always see >1.8ms? Not to mention that increasing the manifold vaccum will help the injectors open faster.

WS6FirebirdTA00

iTrader: (33)

with the larger cam in there my pulse widths are now 2.4-2.3 ms so there is no issue there anymore. i have played with the proportional idle, it oscillates, but pretty slow sometimes. it will get stuck high or low for a while and then recover and oscillate and then do it again. i get about 3 oscillations in one screen shot in hp tuners.

i am noticing with the cam right now there are times that the o2s, i noticed at least the pass side one, will sit at about 450mv and oscillate from there but that was like the center of oscillation for it. i dont know if they werent hot enough or what but its just something i saw and was wondering about. i dont know if its cause proportional idle is turned off or anything either. my idle stays more consistant with the cam in there than it did before with stock internals and the injectors, i guess like you said the map increase made the injectors have to pulse longer for the same amounts of fuel.

still wondering how that window i have of low ms pulse widths at part throttle low rpm will react with further tuning...

jimmyblue

iTrader: (11)

The way I understand it, the injector offset value
is meant to model the opening time (maybe not that
well, but it's your "handle"). See this by the variation
with system voltage, that's the coil ramp-to-current
time (plus inertia, plus the added effort to overcome
higher fuel pressure, which is your other axis).

Now, going from a little Brand A injector to a larger
Brand B injector is almost certain to pick you up a
change in the seating pressure (see time-to-current),
more force on a larger area piston (ditto, plus the
fuel pressure dimension) and so on. The flow rating
arithmetic is simple, from ratings. The offset value
you have to get at empirically, on your own.

To succeed here I think you want to have some
degree of confidence in your airflow metering. That
being the case, you could use your dynamic airflow
and the injector pulse width delivered. The two
should track. There should be a straight-line looking
ratio at the higher airflows. This is your slope, and
the injector offset value is your intercept. At the
low end the pulse width / dynamic airflow is probably
breaking away from the line.

If you tell it a higher injector offset value, the
pulse width delivered is adding this to the base
fuel mass pulse width required by the airflow and
fuel air multiplier. A big offset value will mean
added electrical pulse width delivered.

You could look at the LTFTs at the low end vs the
midrange, where your actual pulse width well exceeds
the working offset value. If the LTFT difference is 8%
(-10 at idle, when you can get it to idle, vs -2 at
cruise) then figure it's the offset value that's an +8%
error term on the total fuel shot. Go to the offset
table, and look at the indicated pulse width there
vs the actual pulse width. Multiply the actual pulse
width by 0.08; that's your pulse width error from
the fuel trim drift at low fuel flow.

Now take that pulse width error absolute and divide
by the offset table value at the operating system
voltage and pressure. Presuming that your error
was all offset, you've now got a fractional offset
error term. Subtract it from 1.000. Say it gives you
0.765; multiply the whole offset value table by that
scale factor.

Obviously there are a whole lot of dependencies
and assumptions embedded in this chain but I think
if you go through the exercise you can get to a sane
offset value without lab data, just based on what
the PCM is trying to tell you.