Definition: The Injector Breakpoint for A9L family processors is NOT actualy an injector breakpoint.
The injector_breakpoint doesn't determain which slope is used, it is a fuel adder that runs off of the
dominate slope at idle. No matter what you set the breakpoint to the Injector slope low becomes active at <2MS.]
this is only for the A9L family.THIS IS ONLY FOR THE STRATEGIES THAT HAVE THE BREAKPOINT VARIABLE IN THE FUNCTIONS AND NOT IN THE SCALARS.
Platform:
Min Value:
Max Value: the max for the A9L family is either 20 or 24 I don't remember exactly, you shouldn't be anywhere near the upper limit, if you are you're compensating
for a problem that needs to be corrected.
Description: the larger the breakpoint # the leaner the AFR, keep in mind this is a fuel trim, it's not meant to make large changes just fine tuning ~2-3%.
Hints:
Here is the whole story behind the A9L injector_breakpoint, the pre-production A9L was to use the breakpoint
to determain which slope is used, this was for better fuel control for the tighter emission controls but there was a
problem that prevented it from being used[ I can't remember if it was software or hardware] so it never got implemented
but was tagged & documented as injector_breakpoint.
Because the breakpoint wasn't going to be used this freed up some memory in the processor so engineering used the extra
space to improve drivability & lessor extent emissions. What they did is use the breakpoint as a fuel adder from idle to
1500 RPM, because it was already tagged as injector_breakpoint they didn't bother changing the name.
The big joke to the insiders at this time was " this will drive the chip burners crazy trying to reverse engineer"
This is a true story.
What all this means to the A9L tweecers is don't change your maf_transfer at idle to correct KAMREF, use the injector_breakpoint
thats what it is for & you will get a more accurate tune.
If you are running rich then you might have an offset to high and vise versa. If rich and the offset is to high then
the injectors are being held open to long. This would mean that either the MAF is off or the offset is not correct for
your injectors. If your injectors are not factory then they will difenatley have a different offset.The A9L has a very interesting history, there was alot of politics involved that had an impact on how it was formated.
There is a few more parameters that aren't what they appear but the injector_breakpoint is one of the best hidden & most misunderstood.
(quoted from the TwEECer tuning list)
Brian
Injector Breakpoint (NON A9L family)
Definition: The Injector Breakpoint is the point at which the EEC switches from the injector high slope to the injector low slope for fuel calculations.
The units are pound mass of fuel per injection.
Platform:
Min Value: If you set your breakpoint to zero the high slope will always be used. The low slope will still have a small effect on the pw calculation, but not much.
Max Value:
Description:
Hints:
The breakpoint identifies the transition point (in lbs. of
fuel) between low and high slopes. If high and low slopes are set to
the same value, the breakpoint doesn't have any effect. Depending on
offset this can be made to work within acceptable limits, at least as
far as emissions which is Ford's biggest concern. 94-95 Cobras came
from the factory with both high and low slopes set to 24.
You need to set the breakpoint where the high slope value is no longer accurate for the fuel calculation.
The EEC assumes the high slope for all fuel calculation and it assumes it is linear with respect to pulse width.
The problem with our injector type is that the start flowing differently under smaller pulsewidths which throws out the actual amount of fuel delivered versus the calculated. One could have a function or table of injector flow versus pulsewidth but instead there is a second injector value available for the EEC to use in its calculation. When the amount of fuel to be injected is less than the injector breakpoint, the EEC starts using the "other" variable, the low slope, to calculate the pulsewidth.
I you graph the fuel delivery versus the pulse width, you will find it pretty linear with the exception of the very low end of the pulse width where the slope of the curve (line) is changing. The linearity is not the same and the fuel error gets bigger and bigger with smaller pulse width. The bigger the injector, the worse it is.
The key is to find the point where your injectors (average of all 8) curve linearity is changing. Bench testing is probably the best way to do this.
For example:
To get my breakpoint set to 2.5ms I had to work out how much fuel (lb mass) is delivered in 2.5ms
First I worked out how much fuel is delivered in 1ms:
1000ms in a second
60 seconds in a minute..
60 minutes in a hour
42.29lb/hr injectors
lb mass per ms=42.29/(1000*60*60)
which works out to be 1.174722222e-5 AKA 0.0000117472 lbs of fuel per ms.
so to set it to 2.5ms I multiplied 0.0000117472 by 2.5 which gave me 0.000029368
Set the breakpoint to that and tada! A useful injector low slope!
The breakpoint tells the EEC when to change between the high and low
slopes. Both values are used at all times, but the low slope value
dominates the calculation below the breakpoint and the high slope
dominates above the breakpoint. If you're rich at pw below the
breakpoint increase your low slope and vice versa. If you're rich at pw
above the breakpoint increase your high slope, and vice versa. If
you're rich across the board, increase both, and vice versa. Have you
tried plotting your KAMRF vs. PW using Walt Barnes' spreadsheet (in the
files section of this list on Yahoo Groups under "Other". The graph
makes it very clear what is happening. It's also important to be aware
that the breakpoint value is in lbs. of fuel, not ms.
See also:
Injector settings