ZR-1 Net Registry Forums - View Single Post - For tuners, a Holy Grail of Injector voltage Offset

XfireZ51 · 10-04-2013

This may help in understanding why tuning benefits from having the correct Injector Offsets. From a Thirdgen thread

http://www.thirdgen.org/techboard/po...545-post3.html

"There is no set formula for flow versus Injector offset.
Wish there was, but it is a little more difficult than that.
The offset (or "deadtime") is the result of several factors, which include:
o mass of the pintle and its lift off the seat
o fuel pressure
o coil inductance
o magnetic circuit characteristics - function of materials and design (like eddy currents)
o injector driver circuit design

So depending on these, there is a correction curve based on battery voltage that takes in account the above, which defines the "deadtime" as the opening delay time minus closing delay time, in milliseconds.

This is developed for each injector type and is then coded into the calibration. Any change in the above parameters can affect this offset correction curve in the calibration.

If you have a test bench (with an oscilloscope and an accelerometer) you can set the injector up and then feed it increasing PW using a function generator and using the accelerometer can determine how long at various voltages it takes to open and close the injector. This then becomes the battery correction curve, and then the BPW after that is the actual PW that provides the fuel."

Another good explanation of injector offset:

http://www.thirdgen.org/techboard/po...341-post8.html

"The spike you are seeing is the "peak" portion of a "peak and hold" injector pulse. This is a hardware function and has nothing to do with injector bias. The reason for the bias is because the injector requires a set amount of time to open to the point where fuel flows. This time can be as short as a few hundred microseconds for a TBI injector to over one millisecond for a saturated port injector. Say for examplethe ECM calculated that on a port injected setup, it requires a 1.5mS pulse width. Since it takes 1mS for the injector to open, fuel will only flow for .5mS or only 1/3 of what is needed. If a bias of 1mS is added to the final pulse width, a 2.5mS pulse occurs minus the 1mS for the injector to open and fuel flows for 1.5mS. Just what the ECM commanded. Make sense? "

Scott,

Perhaps you could use your oscilliscope to help in developing these correction curves for the various injectors available for the LT5.

Example of VE table w Injector Offset too low. Creates a "bathtub" area of VE.

10-04-2013	#6
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,685	Re: For tuners, a Holy Grail of Injector voltage Offset This may help in understanding why tuning benefits from having the correct Injector Offsets. From a Thirdgen thread http://www.thirdgen.org/techboard/po...545-post3.html "There is no set formula for flow versus Injector offset. Wish there was, but it is a little more difficult than that. The offset (or "deadtime") is the result of several factors, which include: o mass of the pintle and its lift off the seat o fuel pressure o coil inductance o magnetic circuit characteristics - function of materials and design (like eddy currents) o injector driver circuit design So depending on these, there is a correction curve based on battery voltage that takes in account the above, which defines the "deadtime" as the opening delay time minus closing delay time, in milliseconds. This is developed for each injector type and is then coded into the calibration. Any change in the above parameters can affect this offset correction curve in the calibration. If you have a test bench (with an oscilloscope and an accelerometer) you can set the injector up and then feed it increasing PW using a function generator and using the accelerometer can determine how long at various voltages it takes to open and close the injector. This then becomes the battery correction curve, and then the BPW after that is the actual PW that provides the fuel." Another good explanation of injector offset: http://www.thirdgen.org/techboard/po...341-post8.html "The spike you are seeing is the "peak" portion of a "peak and hold" injector pulse. This is a hardware function and has nothing to do with injector bias. The reason for the bias is because the injector requires a set amount of time to open to the point where fuel flows. This time can be as short as a few hundred microseconds for a TBI injector to over one millisecond for a saturated port injector. Say for examplethe ECM calculated that on a port injected setup, it requires a 1.5mS pulse width. Since it takes 1mS for the injector to open, fuel will only flow for .5mS or only 1/3 of what is needed. If a bias of 1mS is added to the final pulse width, a 2.5mS pulse occurs minus the 1mS for the injector to open and fuel flows for 1.5mS. Just what the ECM commanded. Make sense? " Scott, Perhaps you could use your oscilliscope to help in developing these correction curves for the various injectors available for the LT5. Example of VE table w Injector Offset too low. Creates a "bathtub" area of VE.