Min Fuel Milligrams affect on minimum possible PW?

[homebuilt]

Anyone willing to share some insight or experiences with this parameter? I would like to confirm if this field is doing more than creating another minimum PW floor.

[Milan]

Anyone willing to share some insight or experiences with this parameter? I would like to confirm if this field is doing more than creating another minimum PW floor.

I'm so glad I found this thread.

I have been chasing surging issues ever since I switched over to my 2000cc injectors. For the longest time I just assumed that it was a function of the big injectors and that there was no way to get around it.

In trying to do some research regarding another quirk I am trying to sort out I thought back on when I swapped injectors and remembered that I changed the min fuel milligrams when I put the 2000's in.

I followed blackcat's advice and lowered the min fuel milligrams setting in proportion to my minimum pulse width and came up with the value of .003. I'm not sure why I didn't notice it sooner, but this is when my problems started.

I decided to change the value from .003 to .008, which is the value Paul @ Injector Dynamics gave me back when I was on their 1000's and IMMEDIATELY 95% of my surging went away.

I'm not sure what the proper way to calculate this value is, but it seems like there is definitely a point where it can be too low.

[homebuilt]

I'm so glad I found this thread.

I'm not sure what the proper way to calculate this value is, but it seems like there is definitely a point where it can be too low.

I'm glad I wasn't the only one. This could be confirmed for sure if the transient fuel adjust units were known. Meaning how are they going to be scaled to match after an injector change? I think this parameter might be related to that compensation.

Here is the link to the post from Greg I referenced. http://www.hptuners.com/forum/showth...tim#post251632

If the static flow rate was doubled for example, using this method you would cut your original min fuel mg value in half.

[Milan]

The thing is, if I went from the stock injectors on my 02Z, to the 2000's, which are roughly 10x bigger, that would mean I would need to make the value 1/10 of what it was, which is about where I had it and it caused problems for me.

[Pekka_Perkeles]

The thing is, if I went from the stock injectors on my 02Z, to the 2000's, which are roughly 10x bigger, that would mean I would need to make the value 1/10 of what it was, which is about where I had it and it caused problems for me.

Which isn't surprising. And it just isn't the only strange thing with tuning these PCM's. Only god knows how many tricks we need to know...

[5.7ute]

Scaling for injector size does not work for this parameter IMO.
I would just divide the injectors minimum pulsewidth by 31.124308 & place this value into min fuel mg & be done with it.

[homebuilt]

Scaling for injector size does not work for this parameter IMO.
I would just divide the injectors minimum pulsewidth by 31.124308 & place this value into min fuel mg & be done with it.

Would you have any idea why when I did this I experienced more transient and bucking problems? For my injectors the derived min pw (fueling portion with the offset included) is quite small and results in a small value for the min fuel mg field.

If this field is just another min pw then it shouldn't matter if it was reduced smaller than necessary. But the kicker is that it seems to have other effects.

[5.7ute]

Would you have any idea why when I did this I experienced more transient and bucking problems? For my injectors the derived min pw (fueling portion with the offset included) is quite small and results in a small value for the min fuel mg field.

If this field is just another min pw then it shouldn't matter if it was reduced smaller than necessary. But the kicker is that it seems to have other effects.

I had wrote an explanation last night, but I got distracted by work & timed out.
Without being able to view your tune files I can only guess(I use a different editor) My thoughts went around the way the pcm uses these pulsewidth floors.
If you have minimum pulsewidth higher than min fuel in mg, min default pulsewidth will be enabled once this floor is met. Now if the default pulsewidth is set higher than minimum pulsewidth you can get a bounce in the commanded IBPW as it transitions between thw two tables. The larger the injectors, the more pronounced the surge will be.
On the other hand, if min fuel in mg is higher than the minimum pulsewidth table, this PW floor will be maintained until either airflow or fuel demands change.
I will seriously have to revisit the tests I did a few years ago, but time is real scarce at the moment.

[Milan]

Scaling for injector size does not work for this parameter IMO.
I would just divide the injectors minimum pulsewidth by 31.124308 & place this value into min fuel mg & be done with it.

If I do it this way, I get .004 for that value, which will give me surging issues.

My only question now is how did Paul @ Injector Dynamics come up with the .008? However he did it it seems to work well for my 1000's and 2000's.

[homebuilt]

I have corresponded with Paul using his work email previously. He is very busy but he was still able to find time to help answer my questions with the derivation of GM format data from Ford format data.

If you get a response I would love for you to post it.

This is one of the aspects I'm hoping to learn more about at Greg's next advanced GM class.

[5.7ute]

If I do it this way, I get .004 for that value, which will give me surging issues.

My only question now is how did Paul @ Injector Dynamics come up with the .008? However he did it it seems to work well for my 1000's and 2000's.

Sorry for the late reply, but I have been away for a week.
There is the possibility that there is an issue running ID injectors around the 0.125ms minimum pulsewidth floor. Doubling that to 0.250ms or thereabouts that the 0.008 min fuel in mg will give you may be more consistant. There is also the chance that running so small a minimum pulsewidth has you throwing fuel straight out the exhaust. Giving erratic fuelling.
Hopefully Paul can expand on why he chose the higher setting, as the work I have done has proven my scaling to be correct.

[LSxpwrdZ]

When u have such small pulsewidths you really need to play with EOIT to keep the fuel mass being injected when airflow velocity high to atomize the denser fuel mass.

[Injector Dynamics]

My only question now is how did Paul @ Injector Dynamics come up with the .008? However he did it it seems to work well for my 1000's and 2000's.

Based on the information in this thread, http://www.hptuners.com/forum/showth...tim#post251632 I chose a value low enough that it would not limit the injector operation, based on the assumption that it had no effect on the transient fueling.

From what I see in this thread, it appears that assumption was incorrect.

We might try 5.7 Ute's recommendation of dividing the injectors minimum pulse width value by 31.124308, but then we need to define the injector minimum pulse width more carefully.

A pulse width of .6 msec puts us at the "knee" of the flow vs pulse width curve of the ID2000 at 4 bar differential pressure. Above the knee, the injector output is very stable and repeatable. Below the knee, the valve is not open fully, and the output is less stable and predictable.

The flow at this pulse width is approximately 12 milligrams per shot, and is right at the edge of providing a stoichiometric idle on a 550cc cylinder with a "stock" low overlap cam idling at approximately 35kPa manifold pressure. Any V8 bigger than 4.4L should not need a smaller pulse width to achieve a stoichiometric idle, but you may be pushing it when manifold vacuum is low, like at high rpm with a closed throttle.

Edging below that value of .6 msec gets us into the less desirable range, but that is certainly better than running pig rich.

Using .6 msec as a starting point, we get a value of .020.

If your data logs tell you that .6 msec is not low enough, back it down by the percentage error in your lambda value, and recalculate the transient value using 5.7 Ute's factor of 31.124308.

I wish I could be of more help, but my understanding of the system is limited. What I can do is provide you guys with whatever injector data you need to help sort this out. Hopefully we can get a better understanding of this parameter.

I'll keep an eye on this thread and offer whatever I can.

[5.7ute]

Thanks for chiming in Paul.

[DSteck]

FWIW, with 0.008 in the transient value, I'm able to idle stoich on ID1000s with various displacements (346, 408, etc). I haven't used ID2000s in an older application though.

[Injector Dynamics]

Have you noticed any issues with transient response after changing the value?

[DSteck]

As far as feeling, no. I don't think my AFX is fast enough to register a significant problem on a transient though.

[homebuilt]

If I do it this way, I get .004 for that value, which will give me surging issues.

My only question now is how did Paul @ Injector Dynamics come up with the .008? However he did it it seems to work well for my 1000's and 2000's.

Milan, Could you post two logs? One at the original min fuel mg you had with the problem and another at the value that helped smooth things out. I would do the same but my car is disabled at the moment.

[Milan]

Sure...I'll try to get to it on Tuesday, I've been pretty sick the last few days