Wo:Deep

Hey Guys,

After going through all the pain and suffer from tuning all aspects of our beautiful FDs I found a subject what was adressed very often... but a perfect answer wasnīt found (IMHO).

So now I want to solve this problem....

You all know about the small amount dosing of great Injectors.

A lot of people have issues with very very rich idle conditions using 850ccm (or bigger) primary injectors.

Most people give their cars to "tuners".

They are payed to let your ride run as strong as possible + safety and streetability (also on only track cars you should have a at least "stable" idle)

Now we`ll assume that the tuner knows what he is doing. He will
- make your car produce a lot of power
- tune it to "safe" power,... So: no knock, low egts, turbos running @ safe compressor efficiency.
- make it lean but safe @ cruising mode
- make a stable idle


While most of us (when it comes to tuning) is looking for best power + safety, the correct settings for idle and cruise are less important.

So when the tuner gives you the car and it idles and runs nicely most people donīt ask if it idles @ 12AFR or 14AFR.

THIS THREAD IS FOR THE REST OF US.


I donīt want to waste fuel.
I donīt want to have that ugly *** smelliness.

So I want to do it right.


Now the forum says:

"Try to set the lag time to -0.4 or give it a try tinkering with lower values the theory tells us (0.04 for 850s)"

This is not perfect enough for me....

So lets start the theory part. (Iīll make it as short as possible)



A: Injectors:

Larger injectors have other physical characteristics.
One of them is the lag time.

When you start to power them up (add voltage/current starts to flow) It is a special characteristic of every injector how long it takes to fully open the injector.

This lag-time is specified by the injector manufacturer.

normally larger injectors need longer to reach the full fuel delivery.

So lag time is bigger.

The PowerFC has to know that so it can start earlier adding the current that it can ensure a fully open injector during the desired on-time (dutycycle in percent*period-time in ms)

eg.
50%*20ms = 10ms

So the PFC with Injectors with lag-time 1.73ms is activating the injector for 10ms + lag time (in the PowerFC / datalogit called : Advanced InjFrPr)
= 11.73ms



the 10ms are calculated also by the PowerFC

If you have larger injectors you donīt need the 10ms to add the same amount of fuel. You need:

Xms fuel * (old injector size / new injector size)

This calculation is done automatically by the PFC as soon as you add the information about the injector size + percentage (old injector size / new injector size)




B: PowerFC + injector control.


The problem we have with the PowerFC and large injectors.

(The first information is quoted... not based on my own research!!)

1. The PowerFC has a limitation when it comes to really small opening times.

So a large injector which leads to:
eg.

11.5AFR @ idle @ 4%dutycycle will not get leaner by:
lowering the values in basemap + correction map or overall correction because the PFC will not lower the ms time anymore.


2. Checking the firmware, you will see that the PFC will calculate duty as :
'Advanced InjFrPr' / theoretical available msec.

'Advanced InjFrPr' being the value we log and this
value already includes the lag time.

So:

To lean the car out with large injectors.
We have to change the lag-time.

Due to itīs inertance, the injector will not be fully open during the map-based/calculated ontime (which we cannot make smaller than a special unknown value (SEE POINT 1.)).

So we have a way to cheat with the system to achieve a lower open-time of the injector and so (the area under the open-time is the amount of fuel) to get a leaner idle.


BUT:

changing the lag time will affect the whole map.

At this point I`ll say...
lean idle OKAY...

making everything new (new tune)
+ believing in some trial and error experiences of other forum members

NO!!

Here a little picture which describes the whole thing:

(see attachment)



*EDIT*
Sorry the lower right diagram of the attachment should also be called WOT instead of IDLE!
*END OF EDIT*

So my solution:

I wanted to have a nice solution based on theory and not on trial and error.

When You take a look @ the formula the PowerFC uses for calculating the dutycycle you see "theoretical available msec".

So my first thought was...
When I lean my map out by changeing the lag-time. I have to compensate this on the rest of the map. BUT... is this possible??

theoretical available msec, as you can think, depends on the rpm.

On our rotary engines this will be a bit difficult and PLEASE CHIME IN HERE!!! if Iīll tell some trash.
From rotaryengineillustrated
The rotor is rotating at one third the forward rate of the eccentric shaft and it takes 270 degrees of eccentric shaft rotation between TDC and BDC, and vice versa, which is 90 degrees longer than the 180 degree stroke of a conventional piston engine.
While we are concentrating on only one working chamber, for the sake of clarity, please note that each chamber is performing its own cycle, 120 degrees out of phase with its neighbor. In this way, the three chambers contribute to the production of one power stroke per rotor per revolution of the eccentric shaft,...


So the theoretical available time will be:

1/(rpm/60)
so in wort case (for me at least ) its:

1/(8000/60) = 7.5ms

so if you change the lag-time from 1.72 to 1.32 (instead of 1.68 to 1.72)
you will make 0.4/(7.5/100) = 5.34 percent failure in fuelling. so you have to add this by correcting your base or correction map.

Unfortunately I donīt know if the PFC considers the port-open time to calculate the "theoretical available time".

If you know it better... please tell me.

Nevertheless.
this shows me that a correction of the with intent made failure by changing the lag time will be possible.

because when you think about "never go over 90% inj.- duty cycle" youīll see that when you are @ 85% dutycycle you can easily add 5%.
AND:
It will only effect two injectors.
So if you have a value in your inj. map (+ correction) which leads to a dutycycle (full boost and max rpm) around 85% then you will have to add 2.5% to that value to compensate your effect in changing the lag-time.
You only have to compensate 5% if the second injector isnīt used (lower rpm / lower loads)


Iīll make a excel sheet after some agreement of well known members in this forum with which you can correct your map.
Iīll test it @ my own car as soon as possible.

Please excuse the grammar etc. ..

Regards
Marc

Narfle

iTrader: (16)

Good stuff here. A solid idle is key.

Lionheart

Subscribed!

mefarri

iTrader: (2)

Me as well

oo7arkman

iTrader: (2)

With my extremely limited knowledge of tuning and how the injectors are effected by PFC settings this sounds like it makes good sense. I would LOVE to be able to lean out my idle but I am very interested in hearing from some of the veteran tuners and PFC experts on here. Thank you very much for putting thought into this and bringing the question up. You may have really helped so many ppl on here it is crazy..

2a+RoN

I've said it once and I'll say it again... Tuning with lag times is WRONG! The ECU needs this information to be correct to make accurate compensations.

fabiano

+1

giving the pfc wrong injector values is not the right way of tuning.

quick and dirty: you can change the lag time and than simply remap the car.
changing the lagtime and "calculating" the changes for the entire map is the same ****.

Finster

iTrader: (1)

damn goot shizzle here

Wo:Deep

Okay... so now lets discuss this...


First I want to make it clear that I donīt want to defend my theory...

I just want to make it right.

And when you have suggestions and answers or other theories you are welcome to tell them and Iīll be happy to learn something new..
but sorry guys.

Your personal opinion isnīt based on resilient calculation or physical theory with which you could change my mind.
So far.

You are welcome to do so.

@ oo7arkman: YESS!!!! Iīm also waiting for some veterans to chime in and give their statement!!

@ fabiano.... hi my friend...





Iīll agree that changing the lag time cannot be correct when you start thinking about it. The complete algorythms in the PowerFC are based on physical formulas and respect the physical characteristics of the components and the System.

So Iīll agree with you if you would say that the correct way is to copy the physical reality as good as possible.

BUT:

Unfortunately the PowerFC has this limitation in small dutycycle values and there the PowerFC is making it impossible to stay inbetween these physical reasonable values.

AND: my calculations show that changing the lag time CAN be corrected.


Please correct me...

But if you have an Air fuel ration of 12:1 it is completely unimportant from where and when the fuel comes ....
The important thing is that you get the amount of fuel you need.

Maybe I have to clear the physical thing about the injector once more.

By changing the lag time in the PowerFC the physical properties won`t change.

So the real lag time will remain the same. (time from begin of actuation to fully open injector)
Also the lag time you forget completely is the closing -lag time.
Larger Injectors need longer to close due to their different inductive properties. Reducing the current and so closing the injector needs more time on larger injectors than on smaller injectors.
The PowerFC btw. doesenīt take this into account also. But we wonīt go to deep into the detail.

What I want to say is that:
The amount of fuel is the integral of the opening position of the injector and the related injection rate over time.

If you change the lag time you will not loose the fuel during the opening phase (real lag time stays the same) or during the closing time (closing lag will also stay the same in reality).
The fuel you are losing will be inbetween the "normal" open time (pulse width.)

So you can correct this by enlarging the pulse width.
The most important thing is that you donīt have to enlarge the pulse width over the critical values (90% injector open time).
that this should be possible is shown on my first post.

Here another graphical try to describe it!

(see attached file)



So the conclusion for me is:
maybe you need bigger secondary injectors if you have already reached the limits of your injectors because you need to add open time (indirect: duty cycle) in the map to compensate the lag time.
But you are possible to do so. Thats my result.


Again please tell me if you know it better.
But telling me that you "think it is wrong" isnīt enough for me.

Please proof your opinion with physical resilient informations.

thank you
+ thank you for discussing!
PS: again. please excuse grammar etc...

regards
Marc

fabiano

thats right, the engine doesn`t care about the calculation of fuel as long as it is an ideal amount. But giving the engine 2 wrong parameters will not make it right...
I have not such a restriction (min duty cycle) in my pfc (sr20det) so I would ask myself why the rx7 pfc has it.

you can change the lag time, you can remap the entire correction or basemap and I am sure you will get right AFRs, but thats not a solution, its just a workarround.

Work with the restriction you have (rich idle) or work around it by altering your lag time and remap the entire fuel map. but that should be done by mapping not by calculating with an excel sheet...

you got all you need pfc, datalogit, wbo2 so why is it so important to calculate it?

Wo:Deep

UPDATE:

While reading my text again, I found a little overkill in my consideration.

Making an Excel Sheet is IMO not neccessary because as you can read in my posts:

The PowerFC works with times and then calculates the dutycycle and period time.
So the initial thought to check how much the dutycycle is influenced by the change in lag time wasnīt wrong but the correction is much more easy than imagined.

Because you donīt have to make the calculations yourself (dutycycle / period time) and due to the fact that the lag-time directly influences the "normal" open time. You only have to add the lag-time difference * 2 (because two injectors are making this "fault") onto each cell in the base-map. (apart from the cells you want to lean out)

The difference in percent is now calculated by the PFC but the amount of fuel should stay the same.

That easy...

and I have to make a statement.

Adding this to the cells DOES NOT mean that retuning the map or at least checking the AFR once again isn`t requiered.

The intention to do that is much more, to have a better (theoretically the same) point to start from. This is as you might think not the correct doing for an initial tune.
but for people like me who have an already working tune. It will be possibly really helpful and will save some time. (or prevent engine damage due to starting a new tune with wrong values which cause lean conditions. etc.)

regards

Marc



*EDIT*
Hi, I saw that you have answered while I was writing my text.

You are right...
If I would have the oppertunity to make everything new, I would really tell anyone:
Take 550(stock) primary injectors and >1300 secundary injectors (If desired power and so fuel consumption is making this possible)

But what was important for me and the most other people was:

I have my setup as it is and Iīm satisfied apart from the rich idle and cruise. How can I solve this problem without making anything wrong.

And while the PowerFC isnīt using the lag time (as far as I know. please correct me) anywhere else in it`s algorythms apart from the injection time - duty cycle calculation. There is no problem you cannot solve. Or in other words.

By changing the lag time + correcting the map. The whole system (Fuelling, Air, combustion, AFR) won`t change!

Wo:Deep

*EDIT 2*


without ******* around but...
Are you really sure about that.

Put some 4x >1000 injectors into you SR20DET and maybe you will have similar problems.
Maybe you have never reached such low opening values??
+ As I said thats not based on my own research...
I dont know ... but there has to be such influences
Otherwise it is not explainable that lowering in base-map values donīt have influence in idle AFRs?!?!?

And as I said.
If you know the ONLY REAL reason.
+ How to correct it physically right.... then give us your wisdom!

Until then... Iīll change the lag time (and supposably everybody else will do so), correct the map and be happy with a running car as before. With no fear of making something physically wrong + heaving a nice lean idle!

fabiano

there is no way to do it right with the pfc in my opinion, you got a restriction from the pfc... you just can workaround or life with it...

powerfc is just a cheap way to take control of your maps within some restrictions. if you don`t want such restrictions change to a real ecu (aem/haltec/motec...)

what about the other correction map (temp, acceleration,....) all of these must be touched too if you change the lag, if you want it perfect...

i am able to go lower than 4% duty cycle with my pfc...

in your case you have the equipment to do it right.

I would not recommend other users to touch any map or correction of the pfc without a bit knowledge and a wbo2...

fabiano

anyone else?