Injector Offset Tunning
09-20-2007, 05:01 PM
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Injector Offset Tunning Hey guys,
Can anyone explain a good way to adjust the Injector Offset vs. Battery Voltage table to compensate for new, larger injectors. I have 50# RX injectors and have used AEM software to give me a compensation value for the new injectors. But I don't know if I'm suppost to add, subtract, or replace the old value with this new one... I've given a rough example of both the stock Offset table and the AEM table
STOCK
volts usec
11 4500
12 4000
13 3500
AEM
volts usec
11 650
12 600
13 550
Does usec mean MilSeconds? i.e. 4500 usec = 4.5 ms?
Is there a logical way to tune this using scanning software, wideband o2, ect? Thanks very much for any imput....
Mike
Can anyone explain a good way to adjust the Injector Offset vs. Battery Voltage table to compensate for new, larger injectors. I have 50# RX injectors and have used AEM software to give me a compensation value for the new injectors. But I don't know if I'm suppost to add, subtract, or replace the old value with this new one... I've given a rough example of both the stock Offset table and the AEM table
STOCK
volts usec
11 4500
12 4000
13 3500
AEM
volts usec
11 650
12 600
13 550
Does usec mean MilSeconds? i.e. 4500 usec = 4.5 ms?
Is there a logical way to tune this using scanning software, wideband o2, ect? Thanks very much for any imput....
Mike
09-20-2007, 08:09 PM
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uS is microseconds, the stock able is calling out
4.5 - 3.5 milliseconds (mS) and AEM, 0.65 - 0.55.
You're not going to find much out there for most
injectors. There are some in AEM's data, maybe
you're lucky there. Every injector P/N is slightly
different in construction and the details affect
opening and closing times, the difference between
which is your offset value (an error in fuel shot
relative to the electrical pulse width, so made part
of that pulse's computation).
The best shade tree way is to look at your old
injectors' idle pulse width and fuel trim sum
(LTFT+STFT) and then the new injectors, same
deal, after of course fitting the new injector flow
rate table. -If- you are sure that the main flow
table is right, then you can assign any drift in
short-pulse fueling (idle) to the change in actual
offset value. Idle long enough with the new injectors
for things to stabilize, look at the trim sum. If the
motor went richer (trims drift toward the negative)
then your offset table should be decreased; this
will shoot less fuel because you add less "padding"
to the ideal flow-table / airflow-based pulse width.
If it swung lean (trims drift positive) then you
scale up the table. Whether adding or multiplying
is better, I don't know. But I'd tend to favor
multiplying.
As to how much, look at the new injector pulse width.
If your trims drifted from (say) STFT+LTFT=-2 to
STFT+LTFT=-12, that's a 10% drift. So you have a
10% error on your actual pulse and you need your
offset value -at that voltage- to be 10% less. So
multiply the whole offset table by 0.9 and check
whether that starts to push you back to the old
trim position. Maybe I screwed up the description
and you should've gone the other way
Thing to look for: if -all- of your trims drift at once,
it's not an offset problem. Offset affects primarily the
low airflow cells - 0, 1, 4 and your idle FTC.
4.5 - 3.5 milliseconds (mS) and AEM, 0.65 - 0.55.
You're not going to find much out there for most
injectors. There are some in AEM's data, maybe
you're lucky there. Every injector P/N is slightly
different in construction and the details affect
opening and closing times, the difference between
which is your offset value (an error in fuel shot
relative to the electrical pulse width, so made part
of that pulse's computation).
The best shade tree way is to look at your old
injectors' idle pulse width and fuel trim sum
(LTFT+STFT) and then the new injectors, same
deal, after of course fitting the new injector flow
rate table. -If- you are sure that the main flow
table is right, then you can assign any drift in
short-pulse fueling (idle) to the change in actual
offset value. Idle long enough with the new injectors
for things to stabilize, look at the trim sum. If the
motor went richer (trims drift toward the negative)
then your offset table should be decreased; this
will shoot less fuel because you add less "padding"
to the ideal flow-table / airflow-based pulse width.
If it swung lean (trims drift positive) then you
scale up the table. Whether adding or multiplying
is better, I don't know. But I'd tend to favor
multiplying.
As to how much, look at the new injector pulse width.
If your trims drifted from (say) STFT+LTFT=-2 to
STFT+LTFT=-12, that's a 10% drift. So you have a
10% error on your actual pulse and you need your
offset value -at that voltage- to be 10% less. So
multiply the whole offset table by 0.9 and check
whether that starts to push you back to the old
trim position. Maybe I screwed up the description
and you should've gone the other way
Thing to look for: if -all- of your trims drift at once,
it's not an offset problem. Offset affects primarily the
low airflow cells - 0, 1, 4 and your idle FTC.
