Injector Tables and all that good stuff!

[1bar]

Maybe I am reading this wrong, but it seems to me, as you read down the different injector tables each consecutive table prohibits the computer from hitting the lowest pulse width possible. Am I reading it wrong? Here are some tables I have questions with, and my thoughts to go with it:

B3702: States that this table will offset the opening of the injector. How does it offsett it? and if it causes the injector to stay open longer, why does the injector stay open longer as the car gets hotter? I get the thought behind "a hotter engine will require more fuel", but if you are trying to barely open a large injector, I think this table might be heading me in the wrong direction??

B3703: What does this table affect?

B4002: This table multiplies (oh boy, not the multiplies part again:nixweiss:) the inj flow compensation based on fuel pump voltage. Will this affect injector timing at idle since I have a -10 hot wire/relay kit going directly to the pump, and an aftermarket truck alternator that pumps out more juice at 800 rpm than my stock one...by like 50 plus amps?

B4005: What "values" are being added to the injector timing on this table? it seems that as the open time of the injector gets smaller and smaller, this table is adding more "values" into the mix. Are the values added some type of multiplier that hangs the injector open longer?

I hope some of you guys can shed a little light on this subject as I am a little confused.:master:

Thanks for the help,
Glenn:notacrook:

[Tordne]

You ask very good questions here. I'd be real interested to hear some commentary on particularly the B3702 & B3703 tables!

I doubt the B4002 table is ever not 1.00. The B3701 would seem to take care of that sort of thing.

I can tell you about B4005. It simply adds pulse width from the relevant cell when the commanded pulse width is below the value of B4006. The theory I guess is that a injector has a minimum pulse width required to open and flow fuel and this table tries to achieve this. My theory anyway :)

I have SVO 42's that I can get control of on decel. I also have the RoadRunner PCM, so I may actually have a look at the B3702 and B3703 tables at some point.

[1bar]

Hey Thanks Andrew,

I am just getting used to this stuff, and I have a lot to learn for sure.

Anyhow, thanks for the information and let me know what you come up with on those other two tables.

Thanks,
GLenn

[1bar]

Also, I noticed, the minimum injector pulse width table B4003 is 1.3ms. With a OS that commands a given AFR, shouldn't I see a 1.3 pulse width if the AFR is off the commanded AFR? The lowest pulse width at idle I have seen is
1.7ish.

If a pulse width of 1.3 is attainable, can the software be scaled down to get the pulse width even lower?

Maybe the injector is the reason that it won't go lower?

Glenn

[Tordne]

The pulse width at the end of the day is a physical characteristic. There is a minimum pulse width required to allow enough time for the injector to open, flow fuel and close. Going below this value is impossible.

The pulse width is a sum of tables. As a simple example you have your pulse width, then add the offset required for the particular battery voltage vs. manifold vacuum, then you may also need the small pulse adjust added. Quite complex really. To give you an idea of how sensitive to change these are: If I change the offset table by as little as 0.20 ms (20 thousands of a second) the AFR at idle will go from 14:1 to 16:1, just like that ;)

[SSpdDmon]

I asked virtually the same questions over at LS1Tech and never really got any answers...


So, some of the resident geniuses have made some helpful spreadsheets when it comes to tuning for larger injectors...and for that, I think I speak for most of us when I say, "We're greatful!" However, there are several other injector tables in our tuning packages outside of flow rates and I'm confused (I hope I'm not the only one) on when to get my hands dirty with these. From what I can tell, there is:
IPW Voltage Adjustment: changes IPW as the battery voltage changes. I figure this one is pretty much what it is and should be left alone.?.?.
Injection Timing (or offset maybe?): changes the actual opening of the injector in accordance with coolant temp. As the motor warms up, this number gets bigger. Why?
Injection Timing Trim: values shouldn't exceed the previous table...used to limit maximum offset?
Injector Flow Rate: Populated by spreadsheet mentioned above. If this table pretty much determines how long the injectors stay open (based on flow) and the timing/offset table determines how early the injectors open, how do we optimize these for better power? Or am I totally off track?
Injector Voltage Correction: can adjust for voltage swings in the fuel pump...innactive from factory.
Minimum IPW: smallest possible commanded pulse width for a given RPM.
Default Min. IPW: table used in place of the Min. IPW table if commanded pulse width is smaller than the values in that table.
Small Pulse Adjust: values added to short injector on times (less than 4ms). If the computer is commanding a short injector duration, why would you want to make it stay open longer? Factory, these are set to increase as commanded injector duration is decreased.
Granted, these tables might be called something different in HPTuners vs. my copy of EFI Live. But, I'm pretty sure we both have these tables. Any ideas on when to use them or what to use them as a fix for (i.e.- lean tip-in, lazy NBO2's, injector swap side effects, etc.?)

http://www.ls1tech.com/forums/showthread.php?t=583617&highlight=injector

[SSpdDmon]

B3702: States that this table will offset the opening of the injector. How does it offsett it? and if it causes the injector to stay open longer, why does the injector stay open longer as the car gets hotter? I get the thought behind "a hotter engine will require more fuel", but if you are trying to barely open a large injector, I think this table might be heading me in the wrong direction??

I'm guessing, this table is refering to the actual timing of when the injector opens as opposed to how long it stays open. By offset, I'm thinking it might mean "delay" seeing as though the number gets bigger as the motor warms up.

[1bar]

Andrew, so if you change table B3702, you will get the change in AFR that you stated? If so, I need to try and change this as my idle AFR is 11 to 1 right now.

SSpd, so if it does delay it, than making the number bigger, like Andrew did will delay the opening of the injector and make the AFR leaner?

Thanks guys!
Glenn

[Tordne]

I tried B3702 today and it made a difference but not what I was expecting. I am interested in testing this tomorrow for another symptom though.

[SSpdDmon]

SSpd, so if it does delay it, than making the number bigger, like Andrew did will delay the opening of the injector and make the AFR leaner?

Thanks guys!
Glenn

That's the thing. I'm totally not sure what some of these injector tables do, which is why I was asking the question over at LS1Tech. I can only guess. I was hoping someone more familiar with the way the PCM works might chime in... :)

Logically thinking though...I would assume that you don't want an air fuel mixture sitting in the cylinders as long when the engine is hot for fear of pre-ignition. So when I see bigger numbers at higher temps, I'm assuming they're delaying the start of the injector pulse by that many miliseconds. The other side of it is, I would think you want the injector pulsing on the pistons down stroke so that it is creating a nicely distributed mixture of air and fuel as fresh air is being drawn into the cylinder. If it is too early, some of the unburnt, fresh fuel may escape out of the exhaust valve. If it is too late, the piston will be moving up on the compression stroke and the mixture might not be mixed as well. I don't know how the "late pulse" scenario would affect AFR, but I'm 99% certain both the early and late scenarios won't make as much power as the perfectly timed scenario would.

[1bar]

Logically thinking though...I would assume that you don't want an air fuel mixture sitting in the cylinders as long when the engine is hot for fear of pre-ignition. So when I see bigger numbers at higher temps, I'm assuming they're delaying the start of the injector pulse by that many miliseconds. The other side of it is, I would think you want the injector pulsing on the pistons down stroke so that it is creating a nicely distributed mixture of air and fuel as fresh air is being drawn into the cylinder. If it is too early, some of the unburnt, fresh fuel may escape out of the exhaust valve. If it is too late, the piston will be moving up on the compression stroke and the mixture might not be mixed as well. I don't know how the "late pulse" scenario would affect AFR, but I'm 99% certain both the early and late scenarios won't make as much power as the perfectly timed scenario would.

Interesting point, and it seems to make sense. Once I get the new rearend in the car I will work at changing these to see what happens.

This is some good information,
Glenn