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GT-R Gear Learn and Fuel Trim Problems/Solutions

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1) Problem - Fuel trims not working at idle and skewed largely
negative after a long idle period.
 
Solution - Lower "minimum injector pulse width" table.  Larger
injectors require a relatively small pulse width to achieve target AF
at idle and low load.  Sometimes the desired/calculated pulsewidth is
smaller than the minimum injector pulse width indicated by this limit
table.  By reducing this value, final injector pulse width/open time
will be smaller.  This will deliver the correct mass of fuel to
maintain closed loop idle conditions along with small short term fuel
trims.
 
This tuning issue has been observed with injectors 1000cc or more and
is more likely to occur with greater altitude and low ethanol content
fuels - both conditions reduce required fuel mass and injector open
time.
 
2) Problem - Gear learn fails repeatedly or produces undesirable results.
 
Solution – Make sure the vehicle meets the requirements for Gear Learning:
-    The transmission must be up to temperature (50-85 degrees C.  122-185 degrees F).
-    The car must maintain a constant and consistent idle with an RPM range between 650 and 2000
-    The car must be parked on a level surface
-    The engine must be running and in Park
-    The touch points should be zero
-    The engine must be in IDLE mode (ie, the throttle mapping MUST call for
zero throttle opening at 0 throttle position.  Any value other than
zero and the car will repeatedly fail.  On ALL OTS maps, zero throttle position will equal zero throttle opening.)
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