Originally Posted by Fast_Freddie

First lets go over some common acronymns that will be associated with this evolution...

STFT= Short term fuel trim- what the ECU is doing right now to get as close to stoich (14.7:1) as possible, adding or subtracting fuel over the base fuel map to reach that target.

LTFT= Long term fuel trim- a stored value that the ECU has learned to do to reach that target. It takes longer to show changes.

O2 feedback= This is the same thing as STFT in Evoscan

In order to see a more precise percentage of fuel that is being adjusted in Evoscan I highly recommend changing the STFT, LTFT (Low, Mid, High) equations to this... 0.1953125*x-25

First things first, when dialing in your new injectors you need to let the car Idle and you will need to do a long cruise for the fuel trims to register. Don't beat yourself up for weeks to get perfect fuel trims, it will never happen. Strive for +/ - 5% for LTFT Low and LTFT Mid. However +/- 10% is acceptable by most.

From what I have observed the evo cycles fuel trims while at idle about every 6 minutes, i usually let my car idle for 24 minutes (4 cycles) and check the trims, if idle trims are good I go on a nice 30 minute drive and try to keep the MAFhz reading steady throughout.

Injector latency is a certain constant of injector pulsewidth added to the calculated pulsewidth to compensate for the time delay in opening and closing of the injectors. Larger injectors open and close at a slower rate so this constant needs to be increased appropriately. Its biggest affect is on the idle, too high and the car will idle rich or not run at all; too lean and the idle will be lean or not run at all.

Originally Posted by MalibuJack

Once you have the injectors scaled, look at your fuel trims, if their more than +25% you can adjust the scaling a little more until your closer to +/- 10%

Then you have to watch your fuel trims at idle, and cruising.. This is where your Injector Latency Voltage comes in.. If the trims at cruise are okay, then you adjust the lower voltage readings (below 13 volts) to increase the amount of fuel at idle slightly

Now, once your trims are within +/- 10% you can then make fine adjustments, but your open loop maps will be "Fairly close" but you have to watch it carefully not to go too lean, but you now have enough adjustment room to tune the car specific to its needs.. But at this point, when you transition to open loop, it should initially tip in a bit leaner, then stabilize a bit richer, but then the open loop maps get tuned.. Again, be careful since you don't want to let it go very lean, or be too lean at higher boost.. If it is, add fuel to the map, or adjust your injector scaling slightly (make the number a little lower) until its somewhere you want to work.

At this point, you should have STFT's that hover around 0%-5%, and LTFT's that are within 10%... You can adjust your idle speed slightly, and timing at idle to help the quality of your idle after you get to this point.

The result will be a drivable car, with a roughly stock-ish fuel table.. Then you go tune the car like you normally would...

Any additional closed loop adjustment would be in the fuel table, in closed loop fuel control, when you alter those settings in the fuel table, your just altering what would happen if your car had to run in open loop at idle and part throttle.. Obviously not useful unless you have a problem, but once you have those numbers close, the fuel trims are now closer to optimum and don't adjust as much.. Its not a huge deal if its not perfect, it just makes cold starting and driving the car (before the O2 sensor warms up) a little easier and less prone to poor drivability in those conditions, don't forget to check it a few times through the year as climate changes so you can get the best drivability.

Originally Posted by L2r99gst

1. Choose an Injector scaling number
2. Log trims at idle and cruise
3. If trims are roughly the same, but positive, then you need to lower your injector scaling number.
4. If both trims are roughly the same, but negative, then you need to raise your injector scaling number.
5. If idle or cruise trim is positive, then you need to increase the latency value.
6. If the idle or cruise trim is negative, you need to decrease the latency value.

Note: After #5 or #6, you may need to readjust #1 accordingly.

Note 2: #5 and #6 implicitly answer ludikraut's questions about affecting idle and cruise trims. Basically, let's say that the IPW is 1ms at idle and 2ms at cruise. If you adjust the deadtime to add 100us (.1 ms), then you are affecting the idle fueling 10% and the cruise fueling 5%.

More latency = more fuel
Lower scaling = more fuel

Latency will roughly affect idle about twice as much as cruise and almost nothing at WOT/high airlfow. It's is inversely proportional to the IPW.

Latency is basically telling the ECU how long the injector takes to repsond. So, if you put in a larger latency value, you are saying 'this injector is slow to respond, so add this amount of time to keep the injector open'. So, this time is basically added to the IPW. That's why it will affect idle more than cruise and WOT. The IPW at idle may be 1ms and cruise may be 2ms, for example. If you are adding 100us (.1 ms) to the deadtime, it's increasing the IPW by 10% at idle ( for a 1 ms IPW).

Originally Posted by Ludikraut

Question??? What is the relationship between the injector scaling value and the AFR values in the Fuel Map? Is it a linear relationship?

for example, let's say that I am running larger-than-stock injectors on my car which have been tuned via the fuel map only, not via rescaling the injector size. Does increasing the injector scaling by 10% then mandate reducing the fuel table by 10% to keep the AFR the same?

Originally Posted by MalibuJack

Answer....That is a reasonable assumption, however its not a completely linear relationship because of how injectors work..

If you tuned your map for your injectors (and performance) without the scaling, then you would indeed need to go back and alter the Fuel map if you used the rescaling feature..

If the car was already tuned for 550 injectors, and you added 780's, then rescaling the injectors should bring the tune "Close" to where it was before you added the new injectors, however a retune would be recommended (and likely necessary)

Originally Posted by RoadSpike

Idle is primarily controlled with the injector latencies then shortly afterward, in terms of load and rpm, by the maf smoothing/compensation table.

Originally Posted by 03lances

I had a fuel delivery issue for a LONG time with the 440's. I still run stock fpr and rail. Have you had them flow tested? I never did and in order to have my fuel trims in check even with 396 scaling my latencies were pretty high. The only way I fixed it was when I stopped using the 10-15% below rated flow method and used my own method to figure out where my injector scaling had to be. That number ended up being 360 and my fuel has been great ever since.

Originally Posted by RoadSpike

Injector latencies, since at idle the pulse injector width is soo impossibly low to account for the really miniscule amount of air ingested the inectors themselves start being effected more on the time it takes for them to actually open then the size or scaling of the injector. At this point the ecu is adding as much time to open the injector as its calculating the pulse will be. So latencies become super critical when dealing with idle AFR. Generally you deal only with the 14 volt section of the injector since thats where the car will normally operate. Once you get it tuned graph it and curve the rest in relation to your new point.

Originally Posted by burner67

Finally uncapped the wrx 440s myself. it was super easy. maybe did it in 20 minutes and very well worth it.

what i did what put my dremel with one of those tan/pink grinding bits in a vise and just spun the edge of the tip of the injector in a circle until the little cap came off.

I am now staying under 60% injector duty cycle. Where it was up to 115% at 16psi.

I have my scaling at 835 and working on latency value

Originally Posted by 03lances

I believe my maf scaling table has much to be desired still so I think I will be revising that before I tackle the fuel map revision as now it is way out of whack. My latencies are slightly different and my injector scaling is up to 370 from 361 and my maf scaling in the idle hz range is quite a bit lower than before. I still have some work to do but my injectors are looking pretty good. LTFT low is sitting at -3 and my LFTF mid is sitting at +1.75, I could probably get them close but meh I have been getting a couple error codes lately while trying to flash that is making me nervous and wanting to limit the number of flashes.

Originally Posted by slatermvp

imma get the 440s cleaned and flowed tested and then see what they do.

My stock injectors are set up as 232 right instead of the 240 which is what the stock rom has.

Originally Posted by 03lances

Really? My stock rom had 232 in for scaling stock.

Originally Posted by HornstarBU

When the scaling is higher, the injector is assumed to be larger, so less fuel is "squirted"...which means changing to what I have would lean you out I think. It works butter for me, but I guess to each his own (also speed density really makes mine able to be set as whatever, wherever, whenever).

Something is up with a limit somewhere, lets holla at RoadSpike, might even post in his thread on this, as that's where it really needs to be addressed, aye?


When you log, what does your load go up to? Even if you don't have good AFR logs, tell us this.

Max IDC % you see
Max Load you see

Originally Posted by 03lances

Just for a trial try leaving everything else the same and drop your scaling down to like 370-390. then go out and try a WOT run. I had these issues before while tuning and I basically found my injectors needed a 360 scaling in order to get that fuel in there under wot boost. After I threw the "standard" scaling out the window with my 440s I got some real results and have never turned back.