For tuners, a Holy Grail of Injector voltage Offset

[XfireZ51]

Originally Posted by Hog

Yes you are correct if you know the Ethanol percentage, I was was wondering if you could adjust the stoich point until the trims were close if you DIDNT know the exact Ethanol percentage. thats how the virtual flexfuel ECM's do it as they dont use an actual ethanol sensor anymore.

peace
Hog

I suppose you could but that's assuming the trims are already uniformly close which is usually not true. It would be making a "global" change to the fueling. Driving long distance you will encounter varying ethanol percentages. I suppose you could have several calibrations with the stoich already modified for the ethanol ocntent you are currently encountering and switch to that one. An Ostrich would come in handy for that. The only O2 window values I have modified are for idle. This was done for to compensate for greater overlap not E content. All other values are stock and seem to work fine as confirmed by viewing my WB O2. Al could also comment on that.

[XfireZ51]

Well I thought I would update all on this. Over the last few weeks I put together a bin that incorporated the Injector Offsets very similar to the ones listed in this thread for the Accel injectors. I also modified the MAT table to reflect the sensor being used an IAT. Weather is cloudy today expecting snow and temps around 31F. Downloaded the bin into the Ostrich and started the motor. With the increased time offsets, I expected the motor to be a bit richer and it was. However, what a difference in the idle! I have a single mass flywheel and in combination w a ZF-6 Black Tag 6speed, you can get a rattle coming from under the car at idle. The smoother the idle, the less the rattle. During warm up, I got little to no rattle. Motor idled down smoother than I recall before. Once it went C/L, WB was showing 14.7 with a tight variance. It was better than I had expected. Looks like I can lean out the O/L CTS table by about 8%. We're expecting 5-10" snow today and car is on jackstands for replacing brake fluids and rear lines. I won't get a chance to take her out for another week or to see what cruise is like, but I am pretty pleased w the result so far.

[VetteVet]

Dom,

Sounds like you've made some great progress!! Please keep us posted on any further developments. I wish that I could track down the info on the FIC injectors that I have. I called Jon, but he couldn't provide the info.

Jep

[XfireZ51]

Originally Posted by VetteVet

Dom,

Sounds like you've made some great progress!! Please keep us posted on any further developments. I wish that I could track down the info on the FIC injectors that I have. I called Jon, but he couldn't provide the info.

Jep

Jep,

Are the FICs Bosch injectors? In the table I posted, there are numbers for higher pressure injectors. You might use those as a starting point. Look to see how different they are from the stock numbers. Frankly I am not sure why Jon could not provide them. It would make his injectors operate more optimally and be a plus. Actually, I called Jon to ask if he wouldn't do the testing for several of the injectors we use. He said he didn't have the instrumentation for this.
As you know, in tuning, the more accurate your base setup, the better the tune.

[mike100]

Have there been any published offsets for the Lucas style injectors (FIC-Lucas/RC brands)?

[XfireZ51]

Originally Posted by mike100

Have there been any published offsets for the Lucas style injectors (FIC-Lucas/RC brands)?

Mike,

If you look at the table I reference, you will see there are values for both FIC and RC injectors. The question is whether the size injector we use is included.

[scottfab]

Ok, let me open by saying I got up at 1:30am here while thinking about the injector duty cycle at 6000rpm. (when I say thinking I mean dreaming. Yes this is sad but I've always been kinda this way)

Anyway I came up with 20ms. Then I got to remembering there was a thread that had a table in it with various injector lag times and wanted to find it. Well I did. This is it. OK so now read on......

Originally Posted by XfireZ51

Scott,

Yes, its msec. And the variance is the point of posting this.

Yes, variance is the point of the post. I agree. Now, how much variance is too much and therefore a tuned chip is needed vs kinda wanted? (you know to be dead nuts on).

Originally Posted by XfireZ51

An injector isn't just an injector. Swapping different brands, although same fuel flow rating, has consequences in the tune. This is especially true at idle and short pulsewidth situations where the opening time is a proportionately larger part of the total calc'd pulsewidth.

I agree lower rpm and idle would feel the differences (make more difference). Now lets run some actual numbers.

Originally Posted by XfireZ51

Now some on this board might say, "yeah but.." when you tune to 14.7:1 or to a 128 BLM, doesn't the ECM overcome this. Without the correct injector offset, you'll undershoot or overshoot the actual calc'd pulsewidth the ECM is looking for. In some cases, you may "run out of injector" or have too high a duty cycle.

Now this is the area in which the dream centered. It's an accurate statement but..... what are some numbers? Given the worst case OT (also CT) in the table on the link given in your OP what can the ECM do to correct it? (how far down the BLM table must it go?) Does it in fact run out of room? Also how would the component to component variance (inj to inj) of a singe vendor fare? That is, given a batch of inj that were not "matched", when does trouble begin? (largest variance to be tolerated in OT as effected by internal resistance?)
For sake of computation we could even use an OT larger than any listed e.g. 2ms.

To do all this we'd need some info. What is the max swing (in ms) the ECM can effect on pulse with from min BLM to max BLM? I have no idea. Maybe you do?

Originally Posted by XfireZ51

By using the correct offset, you may find that you can lower the overall VE% and have a smoother VE map which means the motor operates more smoothly and predictably in varying conditions.

Yes, we may indeed find.

FYI did you notice in the table they talk about OT and CT being important but the table makes no effort to show CT. Seem it only shows OT. Surely they can not be suggesting they are the same.

So ok, I've written up all that was buzzing around in my head. Time for more ZZZs. I wonder if I'll return to this topic in my dream?

[XfireZ51]

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.

[LGAFF]

At the end of the day, what would the expected benefit be in terms of real world power and or driveability...any thoughts?

[XfireZ51]

Originally Posted by LGAFF

At the end of the day, what would the expected benefit be in terms of real world power and or driveability...any thoughts?

Just like the spark map, the smoother and more consistent the VE table transitions, the smoother the engine performance and driveability.