For tuners, a Holy Grail of Injector voltage Offset

[XfireZ51]

Gentlemen,

The Holy Grail of Injector Voltage Offset:

http://injector-rehab.com/shop/lag.html

If you look through this you can see how different injectors act under varying voltages. You can compare the Bosch v Accel and RCs for example. With longer opening times you get less fuel for the same calc'd pulse width. That's why it's important to get this offset right since it makes tuning fuel more accurate. If you have ever felt that your car has idled roughly after a long hot run, this is one of the reasons why. Once you modify this parameter, you'll need to re-check your fuel tables by datalogging.

[mike100]

I like the listing to use for comparison purposes, but they neglected to show the unit of time.

[scottfab]

I like the listing to use for comparison purposes, but they neglected to show the unit of time.

Must be milliseconds.
Interesting the variance in resistance from unit to unit even
within one vendor per part number.

[XfireZ51]

Must be milliseconds.
Interesting the variance in resistance from unit to unit even
within one vendor per part number.

Scott,

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

[mike100]

Must be milliseconds.
Interesting the variance in resistance from unit to unit even
within one vendor per part number.

yeah, I fired up my TunerPro file and checked the usec values against the table here assumed as msec. Looks like the RC Engineering 23 lb injector falls into the stock table very closely.

I have the Lucas ones- I can't recall if they are 19 or 21 lb rated though.

[XfireZ51]

yeah, I fired up my TunerPro file and checked the usec values against the table here assumed as msec. Looks like the RC Engineering 23 lb injector falls into the stock table very closely.

I have the Lucas ones- I can't recall if they are 19 or 21 lb rated though.

Not sure but when I look at the stock table v the RC values, they're off but 300msec or so. At 14v, its double the stock time of 300 v 620 for
RC injectors.

[mike100]

This was the example I was comparing to:

__________cc. lbs/hr. ohm -> 10v 11v 12v 13v 14v 15v

RC Engineering: 240 23 16--> 1.31 1.10 0.97 0.77 0.62 0.46

[XfireZ51]

This was the example I was comparing to:

__________cc. lbs/hr. ohm -> 10v 11v 12v 13v 14v 15v

RC Engineering: 240 23 16--> 1.31 1.10 0.97 0.77 0.62 0.46

Yes that's right. And at 14v the stock Inj. Offset is .3msec compared to .62. You would note a difference if you made that change in the cal.

[VetteVet]

For anyone wondering what this thread was all about, I just stumbled upon this, which explains it very nicely.


http://www.injectordynamics.com/GMDATA.html (http://www.injectordynamics.com/GMDATA.html)

Jep

[Hib Halverson]

Being that this is a tuning thread, let me hijack it a bit.

What do you guys do for engines forced to run on E10?

Do you work with E10's different stoich or do you just tune for a certain lambda value from your wideband?

[XfireZ51]

Being that this is a tuning thread, let me hijack it a bit.

What do you guys do for engines forced to run on E10?

Do you work with E10's different stoich or do you just tune for a certain lambda value from your wideband?

Lambda is lambda regardless of the stoich which is why tuning for E85 can be simpler than it looks. Lambda is the measure of O2, not AFR. We have 10% ethanol here in the Midwest and I reset my calibration to use 14.3 as stoich.

[XfireZ51]

For anyone wondering what this thread was all about, I just stumbled upon this, which explains it very nicely.


http://www.injectordynamics.com/GMDATA.html (http://www.injectordynamics.com/GMDATA.html)

Jep

Basically you can think of the injector offset as an analog to spark advance.
Injector opening time will vary based on pulse width and voltage. The calibration has modifier tables for both. Different injectors will have differing characteristics for both.

[Hib Halverson]

Lambda is lambda regardless of the stoich which is why tuning for E85 can be simpler than it looks. Lambda is the measure of O2, not AFR. We have 10% ethanol here in the Midwest and I reset my calibration to use 14.3 as stoich.

I understand "lambda is lambda".

What I was asking is how many here on the net who are doing their own cals are bothering with figuring what's stoich, or are tuning for lambda regardless of the fuel.

Also, my understanding is E10 is seldom actually 10% ethanol and that E10 out of pumps varies widely in how much ethanol is actually in the gas. I'm looking for any evidence of that. Do you test your blended gasoline or have you just assumed it's 10%?

[WARP TEN]

I understand "lambda is lambda".

What I was asking is how many here on the net who are doing their own cals are bothering with figuring what's stoich, or are tuning for lambda regardless of the fuel.

Also, my understanding is E10 is seldom actually 10% ethanol and that E10 out of pumps varies widely in how much ethanol is actually in the gas. I'm looking for any evidence of that. Do you test your blended gasoline or have you just assumed it's 10%?

In Illinois we supposedly have 10% ethanol in gas. I work at a BMW dealership and the techs told me that one time a local car came in running very poorly and they tested the gasoline. It was 28% ethanol. Variations in ethanol are not uncommon for us to see. -- Bob

[Hib Halverson]

I had a Corvette tech at a Chevrolet dealer who has Kent-Moore's gasoline tester that he's tested pump gasolines said to be E10 at anywhere from 5% to 32% ethanol.

I got to thinking. If you calibrated for E10 and got stuck with some 5%, no big deal, but if you calibrated for E10 and unbeknownst to you, got a tank of "E32" then ran the car hard? You'd be getting poop-loads of KR and probably burning pistons.

That piqued my curiosity enough that I wanted to get the Kent-Moore tool. I found it's just been discontinued, however, I've found some other "ethanol test kits" on the market that might work well.

Still researching.

[VetteVet]

I had a Corvette tech at a Chevrolet dealer who has Kent-Moore's gasoline tester that he's tested pump gasolines said to be E10 at anywhere from 5% to 32% ethanol.

I got to thinking. If you calibrated for E10 and got stuck with some 5%, no big deal, but if you calibrated for E10 and unbeknownst to you, got a tank of "E32" then ran the car hard? You'd be getting poop-loads of KR and probably burning pistons.

That piqued my curiosity enough that I wanted to get the Kent-Moore tool. I found it's just been discontinued, however, I've found some other "ethanol test kits" on the market that might work well.

Still researching.

In the recreational marine industry, ethanol is a bigger problem than in the automotive world. Mercury Marine sells ethanol test kits. They cost about $9.00 and since they don't use any type of consumables, the kit can be used indefinitely. You can drive over to your local Mercury Outboard or Mercruiser dealer and pick one up(FYI, I'm not receiving anything from Mercury Marine for the plug).

Jep

[XfireZ51]

Flex Fuel Sensor

http://www.zeitronix.com/Products/ECA/ECA.shtml

[Hog]

Even if you figured out the E% of the fuel your putting in the tank, that will change a bit depending on whats already in your tank before filling. The emptier the tank before filling the better.

12570260 Lists at $639 and can be had for $378.

The more modern ECM's run a virtual ethanol meter, using inputs from the O2 sensors to tell the ECM what E% is being fed to the engine.

This is the "Stoich. AFR vs. %Alcohol in Fuel" Table from a 2011 GM truck

Stoich Ethanol
Ratio Percentage
14.670 0%
14.314 6.25%
13.958 12.5%
13.602 18.75%
13.245 25%
12.890 31.25"
12.534 37%
12.177 43.75%
11.821 50%
11.466 56.25%
11.109 62.5%
10.753 68.75%
10.397 75%
10.041 81.25%
9.684 87.5%
9.329 93.75%
8.973 100% ethanol

There is even a table that compensates for the way different alcohol percentages effects the speed at which the fuel evaporates off the cylinder wall.

Can you just keep adjusting the stoich point until O2 trims fall into line? Obviously a pain if burning chips, more for a tuner running an emulator.

peace
Hog

[XfireZ51]

Hog,

You'd want to set the Stoich for the known fuel then tune. That's what I have done. It'd be nice to have a sensor for real time fuel analysis then dynamically adjusting Stoich. Has anyone ever done a FlexFuel using Speed Density rather than MAF?

[Hog]

Hog,

You'd want to set the Stoich for the known fuel then tune. That's what I have done. It'd be nice to have a sensor for real time fuel analysis then dynamically adjusting Stoich. Has anyone ever done a FlexFuel using Speed Density rather than MAF?
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

[XfireZ51]

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]

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]

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......


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).

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.


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?

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?
http://www.corvetteactioncenter.com/forums/images/smilies/night2.gif

[XfireZ51]

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

http://www.thirdgen.org/techboard/posts/diy-prom/459333-final-word-injector-offset/3625545-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/posts/diy-prom/398192-injector-bias-added/3206341-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.

http://www.thirdgen.org/techboard/attachments/diy-prom/120811d1151155397-injector-bias-vs-pe-

[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]

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.

[Hog]

Good info above, I would like to add in reference to resized injectors, there is the belief that when using an injector with known offsets, that if you take the same injector and get it resized, that the previously known offsets are still applicable. This is incorrect.

[XfireZ51]

Here's the PW calc:

BPW = BPC * MAP * T * A/F * VE * BVC * BLM * DFCO * DE * CLT * TBM

Where

BPW - Base Pulse Width

BPC - Base Pulse Constant

MAP - Manifold Absolute Pressure

T - Temperature

A/F - Air Fuel Ratio

VE - Volumetric Efficiency

BVC - Battery Voltage Correction

BLM - Block Learn

DFCO - Decel Fuel Cutoff

DE - Decel Enleanment

Hog,

Also, increasing fuel pressure on an injector will necessitate increasing the injector offset. Takes longer to open the injector. So even if you know the offset for the injector at its rated FP, increasing the FP changes the correct offset.

Scott,

Your 20ms is at 100% DC. Typically you'd like a DC% of about 80 at WOT. So that drops the PW to 16ms at 6000rpm,
12.8ms@7500rpm w an 80%DC.

I can see that the offset for the Accel injectors I am using, the offset is incorrect because my VE table has that "bathtub" curve
at low rpm. right know I have "tuned around that" but I need to bump the offset further to smooth that out. I could make a change to the IB v PW table and modify the smaller PW only leaving the rest alone. In either case, I'd need to re-do the VE Learns tables.
Changing the Voltage Offset would richen the AFR globally although more so at the bottom than the top.

[scottfab]

Thanks for the reply.

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

http://www.thirdgen.org/techboard/posts/diy-prom/459333-final-word-injector-offset/3625545-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

The list of why there is lag/delay/deadtime/latency etc are all valid. But "why" is not an issue (with me). It is a given. The other given is that this delay (OT and CT) vary from vendor to vendor AND even inj to inj if the internal resistance (actually impedance) varies too much.
(BTW not all injectors have pintles)

I do disagree that there is no set formula for computing flow vs offset introduced by OT and CT. Well maybe there isn't one but that does not mean we can't come up with one. Tuning based on empirical evidence is fine but there can/should be a way of reducing that to theory (formula) From that one can determine the max effect of OT and CT on what the ECM is doing. Is it an order of magnitude less or can a delay be large enough to in fact swamp the ECM?

There's lots to consider. Not just supply voltage (regulated or not), and ambient heat and fuel pressure/temperature and plenum heat soak and all the other variables mentioned in the list but I submit other factors we could come up with.

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.

Again the theory of operation here is not in question. It's a given. I could even add a few variables left out. What I am missing right now is what the max pulse width variation the ECM can dial in (form most lean to as rich as possible). Having those numbers in ms is critical for determining the effect of each injectors OT and CT.

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/posts/diy-prom/398192-injector-bias-added/3206341-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? "[/QUOTE]

Yes but again I take this theory of operation as a given and stated on the last post that we need real numbers. For instance. Given the example you listed. If 1.5ms was needed but only 0.5ms was happening due to OT wouldn't the ECM via the O2 sensors see a lean condition and make the necessary corrective action? (BLM) Or is there something I'm missing?


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.

http://www.thirdgen.org/techboard/attachments/diy-prom/120811d1151155397-injector-bias-vs-pe-

I'm in discovery on theory of operation so as to understand the possible worst case effect of OT and CT at the moment. From there some actual lab kind or work could be formulated. Here is what I've discovered (or already knew)
1. The ECM through short term and long term tables makes changes to the injector on time/off times.
2. The injectors have not only OT delays but CT delays as well.
3. Many other factors (no complete list yet) have influence on the injector performance. The list is TBD.

What is missing besides filling in the TBD list? Assuming #1 above cannot compensate for the effect of #2 then #3 needs to be completed to get a formula. From there mitigation ideas could be investigated including ECM table corrections and/or injector supply voltage regulation etc. If nothing else I find it entertaining to get complete understanding of such things. Makes for interesting dreams.
http://www.corvetteactioncenter.com/forums/images/smilies/dance.gif

[scottfab]

Here's the PW calc:

BPW = BPC * MAP * T * A/F * VE * BVC * BLM * DFCO * DE * CLT * TBM

Where

BPW - Base Pulse Width

BPC - Base Pulse Constant

MAP - Manifold Absolute Pressure

T - Temperature

A/F - Air Fuel Ratio

VE - Volumetric Efficiency

BVC - Battery Voltage Correction

BLM - Block Learn

DFCO - Decel Fuel Cutoff

DE - Decel Enleanment


This is good stuff for sure. Thanks! I think I've been exposed to it before in passing. I just was not receptive to thinking that deeply about fuel issues at the time. What was the source for this info? LT5 supplement? Or is it in the FSM? Once I find out the units used for each variable I could run some iterations.

Hog,

Also, increasing fuel pressure on an injector will necessitate increasing the injector offset. Takes longer to open the injector. So even if you know the offset for the injector at its rated FP, increasing the FP changes the correct offset.

Seems like with higher FP you'd get larger flow rates too.

Scott,

Your 20ms is at 100% DC. Typically you'd like a DC% of about 80 at WOT. So that drops the PW to 16ms at 6000rpm,
12.8ms@7500rpm w an 80%DC.

I see. It would seem then that a delay of 1ms would introduce about 1/12 error of the over all value. At lower rpm it would be even less % wise. Interesting stuff for sure.

I can see that the offset for the Accel injectors I am using, the offset is incorrect because my VE table has that "bathtub" curve
at low rpm. right know I have "tuned around that" but I need to bump the offset further to smooth that out. I could make a change to the IB v PW table and modify the smaller PW only leaving the rest alone. In either case, I'd need to re-do the VE Learns tables.
Changing the Voltage Offset would richen the AFR globally although more so at the bottom than the top.

Do you know what the OT is for the stock injectors?

[XfireZ51]

Being that this is a tuning thread, let me hijack it a bit.

What do you guys do for engines forced to run on E10?

Do you work with E10's different stoich or do you just tune for a certain lambda value from your wideband?
Hib,


The topic you bring up should probably be its own thread. It involves using Lambda for tuning if operating in O/L or
manipulating the NB O2 swing points to arrive at the ~14.3 stoich using BLMs for C/L.

On the topic of Injector Offsets, I realized I should have better explained the value of the using accurate offsets. The Injector Bias is one of the variables used in calc'ing the PW at any given RPM/MAP. Particularly for the purpose of emissions, but also driveability etc. the ECM needs to account for the electrical characteristics of critical components like injectors. Voltage to the injectors isn't regulated per se, and so this affects the performance of the injector. Even in a well maintained vehicle, we will have conditions where voltage will vary, ie fans kick on, lights, accessories etc. In order to compensate for the voltage variation, and so the PW realized, the ECM needs to know the "lead time" required by the injector in order to deliver a consistent fuel flow. Inaccurate offsets can be one reason why the motor seems "happy" at one point, but then rough or ragged at other times. VE tables provide a base fueling and INT and BLM will modify that fueling given feedback from the O2 sensor. But there's a lag to this. The ECM does not immediately modify the fuel. It takes a certain amount of time for the INT to affect the BLM. And that's if yopu are running C/L. In O/L, there is no modifying of the PW based on O2 input. So, IMO, correct offsets are even more important.

Attached are the Inj. Comp tables for voltage and by PW.

[Hog]

Hog,

Also, increasing fuel pressure on an injector will necessitate increasing the injector offset. Takes longer to open the injector. So even if you know the offset for the injector at its rated FP, increasing the FP changes the correct offset.

.
Yes, agree 100%, increasing fuel rail pressure affects both the opening delay and the nonlinear flow region of injection.

Non Linear flow regions

A frequent problem involves the difference between rates calculated for tables to perform calibrations and the actual flow rates. Errors of 12 percent are possible. Additionally, flow rates at idle and cruising can differ regardless of the presence of fuel injectors designed to perform at the same rate.



Simply using Bernoulli's equation (the flow rate increases with the square root of the pressure ratio-
http://i1202.photobucket.com/albums/bb373/Paul_Schermerhorn/bernoulli.gif (http://s1202.photobucket.com/user/Paul_Schermerhorn/media/bernoulli.gif.html)

-isnt enough, a calibrator must also factor in injector dynamics such as offsets as well. Basically the more accurate the info about your injection hardware, the more accurate your fueling will be.
Garbage In=Garbage Out.

[XfireZ51]

"
-isnt enough, a calibrator must also factor in injector dynamics such as offsets as well. Basically the more accurate the info about your injection hardware, the more accurate your fueling will be.
Garbage In=Garbage Out."

Hog,

If there is one point I would make re: Tuning, you hit the nail on the head. The fundamental operation of the motor and the baseline values for the parameters need to be as close to optimal as possible. The objective of the tune is to minimize the amount of intervention the ECM must exert in order to achieve proper performance.
As you point out, there's enough systemic variation due to tolerances found in the components, electrical supply, fuel supply etc. The ECM needs to deal w that. Now if you compound that w improper or inoperative components, incorrect settings etc, there is too much variance for the ECM to address. Accurate baseline information is critical(IMO) to a smooth running motor.

[KJL]

"
-isnt enough, a calibrator must also factor in injector dynamics such as offsets as well. Basically the more accurate the info about your injection hardware, the more accurate your fueling will be.
Garbage In=Garbage Out."

Hog,

If there is one point I would make re: Tuning, you hit the nail on the head. The fundamental operation of the motor and the baseline values for the parameters need to be as close to optimal as possible. The objective of the tune is to minimize the amount of intervention the ECM must exert in order to achieve proper performance.
As you point out, there's enough systemic variation due to tolerances found in the components, electrical supply, fuel supply etc. The ECM needs to deal w that. Now if you compound that w improper or inoperative components, incorrect settings etc, there is too much variance for the ECM to address. Accurate baseline information is critical(IMO) to a smooth running motor.


Forgive me, I am way out of school here but what is the objective of achieving a perfect offset? Fuel economy? Power? How do you access/program this information/data?

[XfireZ51]

Forgive me, I am way out of school here but what is the objective of achieving a perfect offset? Fuel economy? Power? How do you access/program this information/data?


Voltage utilized for operating the injectors is not regulated. It will vary based on load put on the charging system. In the meantime, variable voltage affects the performance of the injector which in turn makes fuel flow variable. For consistent performance and emissions, fuel flow needs to be consistent. The Injector Voltage Offset provides the ECM with the time interval to use in order to compensate for the lag created by less than optimal voltages.
If you have stock injectors, no need to do anything. However, many of us use other than stock injectors and so the electrical characteristics at various voltages needs to be accomodated to maintain a consistent fuel flow. In a previous post, I have attached a .jpg of the tables used in the LT-5 calibration that are used for this purpose.

[efnfast]

So Dom, all of this gets addressed with a custom tune?

[XfireZ51]

So Dom, all of this gets addressed with a custom tune?

I can't speak for other tuners although having looked at calibrations, many don't approach these parameters. Some might do "workarounds". A good number of these parameters aren't defined in the .xdfs or .tdfs generally available.
Finally, it takes time and gas. I'm pretty finicky about how I want the car to react to inputs, so I probably spend more time than necessary. But its getting easier because as we develop "standard" configurations for modified LT-5s we can at least start with a calibration that's in the ball park then fine tune from there. Don't need to constantly re-invent the wheel. As an example, I was able to use the tune on my 5.7L and translate for use in a 6.2L because of similar porting, cams etc.
Hope that answers your question.

[efnfast]

Yeah, when I have Pete do the heads, hopefully she can go over to you for a tune.

[XfireZ51]

In trying to find the right Inj. Bias for the 23# Accels I have, I think I have settled on 20% higher than what the IB is for the stock Bosch injectors on the LT-5. My observations in coming up w a more accurate IB is that the BLM split L/R banks seems to be much smaller. It still appears to diverge at idle but the spread isn't what it was. However, above that point the BLMs track very closely with a +/- of 4 from 128. Actually the avg turns out to be 133.4/125.6 or an average BLM of 129.5. This average includes idle which is about a 136/120split, so you can see that cruise is much closer. Slightly lean but I think that makes for a mellower exhaust note. Also, getting to the right tune happened much quicker. I've gone through maybe 6 iterations and now at the point where we are trading the constant .39 back and forth.Once your there, no sense in doing the seesaw.
The motor runs smoothly and doesn't have the blub blub blub note from the exhaust at low rpm/higher MAP. Summarizing it looks like chasing a more accurate IB has the advantage of:

1. Tightening the spread between the L/R bank BLMs. For me, this would also be a big argument for wanting to run C/L. In C/L, the O2s are working to bring both banks into tighter alignment in terms of fuel mixture. Without the O2s, as in O/L, you'll be working w the optimization of whichever bank you've decided to put your WB into. And someone tell me if there's a MASK ID out there that has VE or LV tables for each bank? That would be a bear. Got my hands full w 4 VE tables right now. Granted there will still be some variation due to injectors and even the O2 sensor itself, but at least you have an ECM doing self-correction. Anyway, maybe a separate thread on this topic.

2. Makes getting to the right tune considerably quicker.

My only other question is whether to bother w a bit of smoothing or just leave well enough alone.

[XfireZ51]

While going thru this, I noticed on my datalogs that the O2 signal on the R/S would drop to 0v. Sometimes just a few frames, and other times I would get a whole string of 0s. Long enough and the ECM is going to react to what it thinks is a lean condition. The 0s appeared before I started playing around w the
Injector Bias, so I suspects something electrical. I checked the ECM connEctions and pins. Also tested the O2 signal and sensor ground for continuity. They checked out.
Ran a few more diagnostic tests after reinstalling O2 sensor ground line in ECM.

1. Unplugged A/C fuse to eliminate any possible "crosstalk" from the heater circuit. Both O2s remained at .45v after engine START.

2. Reinstalled fuse, disconnected O2 and jumpered the O2 signal to ground. Engine needs to be running otherwise it will always show the ECM bias value. This dropped the R/S O2 to .03v so that was good.

3. Tried both harness extensions I had. The one I made the other day appeared to be giving me a problem. So I made one more extension and installed it. Now its working w no signal loss altho the O2 will jump in and out of Closed Loop if CTS isn't above 77C. Fans kick on and drop coolant temps in this weather. Just need to get heat into motor. Hope to take it out tomorrow and do some logs
but looking at idle the O2 voltage seemed to be tracking closely along w INT. Right was needing to be somewhat richer than left as usual.

[XfireZ51]

Done 2 runs w the new extension harness, and motor seems to be running real well. Whatever I did worked, including eliminating the O2 sensor signal drop I had on the Right Bank. No loss of signal now. However, I am getting a C/L to O/L to C/L flip flop at times. The hotter the CTS the less it happens but looking at the logs, my best guess is that I am hitting the top or bottom of the C/L O2 window.
That's what seems to be going on. Should I leave them alone or increase the spread? Right now its stock at .698v/.198v. Its seems to be more frequent w cooler MAT/IAT temps.
Maybe run less Prop Gain?

[XfireZ51]

Finally! Accel has published their Injector offsets. However, the one for the 150121 is not there. The 24# injector may be close enough. Its a bit more bias than what I "stumbled" on with my testing. I'll try it out once I get the car back on the road next spring or on a nice sunny day.


http://www.accel-ignition.com/products/fuel-injectors.html

[tpepmeie]

Finally! Accel has published their Injector offsets.

Dom,
looks like its missing the low pw compensation curve, no?

That one's quite important as well, especially if you have larger injectors because you will typically be seeing smaller pulsewidths especially at idle.

Not sure this has any connection to your split BLM's. At least I can't envision such a relationship. These offsets are there to ensure the fuel delivered (by both banks) is consistent with the commanded at all conditions.

Todd

[tpepmeie]

However, I am getting a C/L to O/L to C/L flip flop at times. The hotter the CTS the less it happens but looking at the logs, my best guess is that I am hitting the top or bottom of the C/L O2 window.
That's what seems to be going on. Should I leave them alone or increase the spread? Right now its stock at .698v/.198v. Its seems to be more frequent w cooler MAT/IAT temps.
Maybe run less Prop Gain?

I've seen the same thing. The issue, in my case, was that the CTS was warm enough to go Closed Loop (~47C), but it wouldn't enter learn mode until even hotter. Finally determined that there was still a bit of enrichment occurring up to 68C. The learn mode only enables if commanded lambda = 1 (14.7), ie no enrichment.

Not sure if that will help, but you might look at it, and zero the OL enrichment above 56C or so.

[XfireZ51]

I've seen the same thing. The issue, in my case, was that the CTS was warm enough to go Closed Loop (~47C), but it wouldn't enter learn mode until even hotter. Finally determined that there was still a bit of enrichment occurring up to 68C. The learn mode only enables if commanded lambda = 1 (14.7), ie no enrichment.

Not sure if that will help, but you might look at it, and zero the OL enrichment above 56C or so.

Todd,

Correct on all counts. No the ACCEL chart does not include PW correction. I suppose for larger motors w big injectors it may be a factor. Reviewing my logs,
I didn't find any PW that approached the numbers in that table. The smallest being at idle ~ about 4ms. So I didn't worry about that table. At first I thought perhaps that table was dealing w a delta in the PW but that was incorrect.
In playing w the IB/V table, I in fact found a marked improvement in BLM split.
Less so at idle conditions but even there the delta between the two banks was
decreased. However, at cruise it appeared to really make a difference. As I posted earlier in the thread, my overall BLM is averaging 129 for L/R, w a
133/125 split as of the last tune. Frankly, I'm pretty happy w that. In some places, as in higher RPM areas of the VE table, L/R are identical. To some extent, I consider that the larger cams also contribute to the L/R differential. A small variation in cam timing could contribute to the BLM split as well. I can only tell you what I observed when correcting the IB and can't unequivocally point to a causal relationship. However, when I "overcooked" the IB, the split deteriorated. So it seems as if there's a sweet spot.
Regarding the C/L flip flop, I ran into the issue you described about 2 years ago. Playing w the O/L v CTS table, it would go C/L but no Learn no matter what the temp. Well I determined that the Commanded O/L AFR had to be = to the O/L Offset in the constants. Richer than that and it would override Learn. In my case, that's an AFR of 13.67 at 80C. Took me a while to figure it out. That would suggest having the AFR =13.67 at 68C has Learn come on sooner. Would be great to have an ECM bench setup.
The issue I am having now is that C/L will check on/off at times. Looking at the logs, it's happening at low MAP ( so trailing throttle or decel) and I can see the O2v go lean. I have lowered the O2 window at low gm/sec. to address the rich idle issue you get w larger cams. This was actually causing the Code 44 I was getting at times while idling.
I finally figured out that I was forcing the O2 below the .2v threshold long enough to set the code. Raising the window eliminated the code. So now my suspicion is that the O2v voltage is dipping below the C/L window I just raised long enough to take it out of C/L. If I hit the accelerator, it goes back into C/L.
I am thinking that if I lower the Prop Gain, I can decrease the extent of the voltage swing and keep it within the C/L O2 window. Haven't had a chance to try it out, but I usually reduce prop gains, particularly at idle. Someone suggested narrowing the C/L window but wouldn't that make the problem worse?
Prior to this, I was noticing in the logs that my O2 signal was dropping off intermittently causing the ECM to think very lean(might explain some of the BLM issue). Sometimes it was only a few frames, sometimes a whole string. And it was only on the right side, where I have the O2 harness extension because of the headers. Made a new extension and validated the O2 signal and heater circuits. No more dropout.
Beyond the BLM split, having more accurate IB compensation significantly reduced the number of Learns needed to get the tune right. Within 5 or 6 cycles I got to where the VE changes calc'd were within .39% just about anywhere in the table. So no reason to keep going. Once I incorporate these latest IB values, should be interesting to see how much change there is in the VE. At least, it's moving in the right direction.

[Marc Haibeck]

I think that a large factor in bank to bank difference in fuel trim at idle is the use of headers. With headers only two cylinders per bank fire across the oxygen sensor. Maybe because the system has only half of the normal gas samples, the average is not as accurate. The OE manifolds have the primary tubes shaped so that the gas from each of the cylinders jets across the oxygen sensor. The deflectors can be seen if the heat shields are removed from 1990 - 1992 OE manifolds. I observe bank to bank difference of up to 15 fuel trim counts on about half of the engines that have headers and no other modifications.

I have observed that when warmed up from cold, as the coolant temperature goes past 170 degrees, about half of the totally stock engines will swing in and out of learn mode at low loads. If the engine is run at full load to 7000 rpm in second gear a couple of times the system will stay in learn mode. I have not observed any effect on drivability on an engine that is switching in and out of learn mode. It may be important during an emissions test.

[XfireZ51]

Marc,

As I pointed out earlier, Learn checks ON once the Open Loop AFR is commanded to be the equivalent of the O/L AFR bias in the Constants section of the calibration. Any richer than that and Learn will remain off although you could still be in Closed Loop. 170F is 77C which is right about the point where the AFR makes that transition. In colder weather it takes longer to get CTS up to 80C
And if the fans kick on, you have a situation that takes you below the 80C threshold. Need to get heat into the motor in order to maintain temp that keeps the system in C/L and Learn.

[XfireZ51]

Ok - just read the whole thread (obviously it will take several read-throughs to get it too).

In the mean time;

Should I install headers AFTER doing INJ balance test? Does it matter?

Dom - you said nothing needs be done if user has stock INJ's; what's that mean?

Do I need several C/L cycles before looking at INJ's PW? Does THAT matter?

1. No reason not to install headers

2. The values in the calibration for injector offset is for stock injectors. If that's what you have, then no need to modify cal. There's no mandatory need to change if you are using other than stock. Again, it comes down to making sure things are mechanically sound requiring minimum ECM intervention.

3. Not sure what viewing Inj. PW is supposed to do. It becomes an issue at WOT when concerned w injector Duty Cycle %. At these power levels, should be
non issue.

[XfireZ51]

Yeah - I just 'searched' here Franke; I DID do Primaries hot:

http://www.zr1.net/forum/showpost.php?p=190558&postcount=92

results (1')

#2 1' = 012
#5 1' = 016
#6 1' = 016
#7 1' = 016
#1 1' = 016
#3 1' = 016
#4 1' = 012
#8 1' = 016

Good point too, that you made (hesitation vs idle hunt @ 1.6 - 2.4% TO).



Dom said same thing I think, about lean tip-in, or something like that...

The point I made in the other thread is that just at the TPS% you are researching is where the ECM goes from idle state to a run state. It switches from idle timing to the SA tables. Also, depending on what's been done to the cal for the elimination of the secondary port throttle, the stock cal has a delay for the secondary injector turn on. So you are dealing with a transition point in the operation of the engine management system. Given the results of your injector resistance, I would just go ahead and put on your headers and then see where things are at. I'd also suggest taking this discussion to another thread because Injector Offset and Injector resistance values are chalk and cheese.

[XfireZ51]

Thought I'd resurrect this now that I have had a chance to try the new offset values for the Accels and do some logging/tuning. Been able to do a few runs. Came as no surprise that the initial run showed BLMs being rich. I datalogged the last one after doing a "global"reduction of fuel.The lower rpm/kPa region is still rich, particularly decel, but cruise and idle areas are coming in nicely. One observation is that the BLMs on both banks are much closer together. There still is a "split" but the variation on left to right banks is now within 7-10 counts instead of 20, ie 133-125. Still getting a few areas where the injectors just seem to shut off and where the ECM falls out of closed loop. I suspect that the O2 voltage is moving somewhere below and above the O2 C/L window settings. Usually w a blip of the throttle it jumps back into C/L and Learn. I am thinking I'll leave this alone and see if it doesn't work itself out as I get closer to good tune.
What's also interesting is how much steadier the BLMs are and how much more quickly you get to a pretty decent tune level. Finally, I suspect that with a more accurate injector PW calc, my MPG will probably improve. I could see it in the Instant MPG as I was driving this last time.

[Blue Flame Restorations]

Great work, Dom. I appreciate what you do...a lot!

[mike100]

Now that i have an Ostrich emulator box, I was considering playing around with this feature even though my BLM's are pretty close 128-131 at idle and other common cruise load cells.

The question I have is how much different are the FIC Lucas injectors to the oem ones. There was a published offset for Lucas 24 lb injectors, but a quick mental extrapolation had the values fairly close to the stock ones 9maybe that's why it runs ok with stock cams and so forth.

[XfireZ51]

Now that i have an Ostrich emulator box, I was considering playing around with this feature even though my BLM's are pretty close 128-131 at idle and other common cruise load cells.

The question I have is how much different are the FIC Lucas injectors to the oem ones. There was a published offset for Lucas 24 lb injectors, but a quick mental extrapolation had the values fairly close to the stock ones 9maybe that's why it runs ok with stock cams and so forth.

Mike,

If the electrical characteristics of the injector are not different, then I'd leave it alone. The Accels OTOH are different and that needs to be accounted for. Some people use RCs. You can tune around a lot of this BUT if you start on an accurate foundation, it makes things much simpler. What is the "split" between left and right banks?