Crank Vs. Leak; Altitude Driveability And Emissions; Low Pulse-Width Fueling Accuracy; Driveability Index Fuel Sensitivity - Delphi Multec 3.5 Applications Manual

Testing Recommendations and Precautions
8.4.4

Crank vs. Leak

Note:
8.4.5

Altitude Driveability and Emissions

8.4.6

Low Pulse-Width Fueling Accuracy

8.4.7

Driveability Index Fuel Sensitivity

8-4
kPa) range. Temperatures, pressures and engine control parameters
should be recorded during testing to assure consistency and for a record of
results.
The purpose of crank versus leak is to determine the effect of injector leak
rate on vehicle start times, and to determine what is an acceptable or
optimum value. Injectors characterized for leak rate are required for this
testing. The testing is done at elevated temperature conditions to
determine maximum effect. After testing, leak rate versus crank time
would be plotted to determine maximum allowable leak for a given
application.
In addition, as evaporative emission limits become more stringent, injector
tip leak in relation to vehicle evaporative losses should be considered in
the overall vehicle emissions plan.
Hard restart can result from commanding the electronic throttle control
valve fully closed during engine shutdown. Large amounts of exhaust
gas are drawn into the cylinders resulting in a rich fuel condition at
restart. It is recommended to delay full throttle valve closure until after
engine rotation has stopped.
It is necessary to verify emissions and driveability at altitude as well as
sea level during the development process. In addition to emissions,
driveability would consist of cold starts, hot starts, gradeability, etc.
Temperatures, pressures, and engine control parameters should always be
recorded.
The purpose of this testing is to develop and verify the low pulse-width
corrections in the calibration. This would be done at high and low
ambient temperatures, as well as altitude. Long and short-term correction
factors would be monitored for repeatability and deviation from nominal.
Use a well broken-in engine to minimize internal friction effects and
minimize injector pulse widths.
In addition to the normal cold start testing, it is necessary to verify
calibration sensitivity to high driveability index (DI) fuels. (See section
Multec 3.5 Fuel Injector Application Manual
Delphi Energy and Chassis Systems
Revision: 11/05-1