Intersting thoughts on injector scaling and resulting timing effects

[Hitokiri]

This has most likely been covered as every piggyback computer that does injector scaling would have to compensate for this.

I started looking into this when I noticed that my car (RST w/ emanage and 420 WRX injectors) would not run with ANY timing adjeustment at idle. It also attempts to run SUPER lean at idle if I give it overall injector scaling at all. If I go straight to a .75 airflow correction the car will not idle at all. If I taper up to that while driving the car will learn a little and idle at that setting, but it will push 200:1 AFRs.

This baffled me until I read up more on piggypacks.

It seems our ecu's comtrol idle speed with timing a great deal (more so than the IAC solonoid), and that timing is based heavily on airflow signal. What was happening (I am going to try and verrify this with my ODB2 logger this tonight and post some data.) is that with the airflow correction, the ECU thought it was getting less air and changed timing to compensate. So much so that unless it had learned how to run correctly with my injector scaling as I tapered it, it wouldn't run at all.

I did some looking around and found a message by a guy on yahoo groups Emanage forums that details my problem and observation exactly. Here it is:


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Message: 6
Date: Tue, 22 Jun 2004 10:38:22 +0800
From: "Tristan Hewitt" <***auto@westnet.com.au>
Subject: RE: Re: Injector Compensation - effects on timing

Im eager to see results of this.

heres something interesting for you... power FC ignition map from a
skyline.

http://forums.skylinesdownunder.co.n...de9e58f615c4d6
b5378d1c1cf71bc00&postid=146134

L15 appears to indicate 1.2 bar or 17.5psi.. and its safe to say that
L1 is around -0.6 bar (vacuum)..
So the range is 1.8 bar.. or 26psi.

...or 1.73333333psi per cell.

So boost begins at about L6 just after the first horizontal line

lets take 6400rpm

0psi would be about 49 degrees advance
17.5psi would be around 21 degrees...

mid points are 29 and 26 degrees...

So.. lets say you did injector correction on a map like this... using
injectors twice the size (eg 400cc up to 800cc).

The map sensor voltage (or AFM signal) would halve, yes? roughly
anyway

l16 would become l8
l10 would become l5... and so on

l16 = 20 degrees at 6400rpm
l8 = 36 degrees
16 degrees of correction required (eek)

l10 = 29 degrees
l5 = 48 degrees
19 degrees of correction required (eek).. thats almost at the
emanage's limit.

That there appears to be around the largest correction amount

As boost rises, the amount of correction needed in the emanage's
igntion map REDUCES. (according to this theory anyway)

And with injectors anything bigger than twice the size.. you will
possibly need to adjust base timing via crank angle sensor or
distributor to get the extra range. I can see why greddy said no more
than 150% larger.. even that is really pushing the limit on some cars
I expect.

This is of course assuming that stock maps were perfect. But lets
face it, most stock maps require a bit of advance for best
performance anyway... which negates some of the required retard as
explained above.

-Tristan


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Sohow familiar are people whith this? I am a newb at tuning and I apologize if this has been explained to death. Do UTECH tuners have to worry about this with injector scaling? How does that work with the unit only picking up timing after 60tps?

thanks for reading. Please post your thoughts.

Todd

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[happasaiyan]

you can set where you want UTEC to control the show. 20-100% TPS.

you set the timing for the map, and the UTEC will run THAT timing.

[8Complex]

Good concept Todd. I never had to tune with a piggyback, but I do remember talking to the guys at Split Second and John at J&S about the timing changes during scaling the input airflow signal.

Your car, even though pig rich, will need to remove some timing up top as you are leaning it out, otherwise you're going to run into detonation situations. If the stock ECU can trim the fueling back at idle and cruise enough to work, so be it. It'll also change the timing it needs in order to compensate well for it.

[Hitokiri]

I am beginnig to see the advantage of the utech in taking over timing completely.....

and the reason why many SAFC'd cars blow up without timing correction.

It seems any piggyback that does not allow airflow AND timing control is almost useless, except for maybe a simple timing controler like the J&S. If it modifies the airflow signal, you HAVE to be able to modify timing as well.

I can see the emanage's ability to add injector pulsewidth after the ecu as a very good thing. You have the ability to add fuel without the ECU knowing you did (aside from of course the o2 sensor readout.) So if you vary that additional injection with boost so the ecu sees good AFR's it might be a better option than modifying the airflow signal in order to increase fueling. The problem with that is if you can only increase fueling (emanage), with larger injectors you are skrewed.

8- I didn't think about up top but you are definitely right! I will need to heavily modify timing throughout the range with respect to the correction I am running. I look forward to talking with the tuner at XX when I go down there next week to have my car tuned withthe emanage. I can't see him getting this kind of a complicated tune done in a short amount of time especially if he doesn't have an OBD2 logger to look at the timing / fuel trims the ecu is running. A UTECH takes quite a while to tune and it would be substantially easier to work with as timing works standalone.

I am excited to take some datalogs off OBD2 to see what timing the ecu runs throughout the range.

8- I will most likely let the ecu correct at idle. I can see it correcting in long term fuel trim up to 30% and 5% in short term while idleing. So 35% is quite impressive for the stock ECU to handle. under throttle that correction goes straight to 0 when I build boost which richens the mix up nicely. I am still WAY rich to the point of bogging and stalling if I try and push WOT so I need to remove more fuel. Or maybe its the timing bieng off that is causing me to bog down? Well most likely a combination as I am still hitting 9's in ARF occasionally.

my friends tell me the car is shooting flames on the highway....

Todd

[Hitokiri]

on second thought I am going to try to mod timing to compensate for changes the airflow correction is making.

the car just runs too rich under decel and across th board without correction.

my goal is to eliminate the ecu's correction all together. Or within a resonable margine under closed loop.

Todd

[Hitokiri]

i am surprised nobody has any comments about this....


maybe a better place for it would be AFI

[8Complex]

I think it's just a rather strange problem, though I know other people must've run into it before. Perhaps you can see if you can search for "wrx injectors e-manage" on the search page and see if anyone else had any other issues.