Hey All,

I just put a set of 850cc injectors in my car with the Perrin Fuel rail and I am starting to re-tune my fuel map. I am a bit confused on a few things though and I am hoping you guys may be able to answer my questions.

1 - What is the relationship between the Scaling setting and the stock injector size setting in the Open Loop parameters table? Should I be changing both of these for scaling? I currently have the scaling set to 700 and the stock set to 660. This has given my a near perfect idle with my LTFT (Long Term Fuel Trims) coming in at -1 and STFT (Short Term Fuel Trims) gliding between 2 and -2. Once I start driving though its another story. I am running pretty rich, as expected, and I am seeing my LTFT go to -9 so far with STFT running between 10 and -10, depending on load. THis brings me to my second question.

2 - Does it make sense to just adjust the scaling to get the idle good and let the ECU adjust the LTFT and STFT as needed to get stoichiometric? I would like to not have to mod the 0% load column at all if possible. In the long run this may help the ECU adjust a bit quicker but in the end it doesnt matter what I put there since the ECU is running closed loop anyway.

3 - Is the goal to get the LTFT and STFT both to 0? Is it ok to have the LTFT at 10 to drive the STFT to 0? Before putting the injectors in my LTFT at idle was 9 and at cruise it was 6. STFT move all over the place, as expected, so no point in trying to guess the number since the LTFT number gives you the average.

I know these injectors are overkill for my current setup but I am preparing for CAM's and a bigger turbo. Just want to tune it one piece at a time so I dont have too many variables. On a side note I am running stock air box and standard air filter so the MAF doesnt get any abrubtion in the air flow.

Thanks for all your help over the last 2 years!!

Chris

 

bump!

 

Good god, 850's. If you want I can throw up my fuel map for 780's to get you to a small starting point, but I must warn you this map still runs rich on my car so your will be even richer most likely in the low 9's.

 

Hi Dryad!
I would be very interested to see what you did with the 0% column in your tune. I called TurboXS and talked with the guys there to get a better understanding of where to start with the Scaling and Stock injector size options in the UTEC. I was able to easily get my Idle doing really good by setting my scaling to 770 and my Injector size to 670. But I had to add 20% fuel in the areas between 500 and 1000 to keep my fuel trims close to 0. I then started cruising around at different RPM's but staying in the 0% load column and and noticed my LTFT was slowly rising so I added 5% fuel in all the other cells for 0%. This has worked so far but it gets really rich (12:1) when I am doing partial throttle acceleration. I am hoping the ECU adjusts for this overtime.

For performance tuning (WOT) I had to take out 5 points all across the board so far to get it back in the high 10's low 11's. Not a big surprise. Now that I have the bigger injectors I have also been slowly adding boost since I have the headroom for it =) Up from 1.4 to 1.55 now! No timing changes have been needed yet but Ill know more when I get to the track and can safely do a full pull in 4th gear.

Ill get my fuel map off tonight and post it. It would be interesting to see what our differences are. What boost are you running and what did you set your injector scaling and stock injector size values too?

 

Okay.. the adjustments will vary no matter what anyone suggests.. But with 850's you might have to use settings like 780-800 for the stock and modified settings.. That should get you in the range, but fairly rich..

Your next question is about the long term fuel trims and short term fuel trims.. Here's where it gets complicated, you want to adjust your trims so they are as close to zero as possible.. within 10%.. Only here is where it gets complicated..

Large injectors are very latent.. So you'll have to get your LTFT's as close as you can at part throttle driving in your cruise RPM, since that is where your car will spend most of its time, do that by adjusting the Stock injector size settings (This alters the MAF reading)

Once you get your driving LTFT's within 10%, let the car sit and idle, watch the STFT and LTFT as it drifts, and make adjustments in the 0% column on your maps until you get your trims within the same number as they were earlier when driving in closed loop...

With your OLF maps, thats your modified injector size, you just want to get that setting roughly to the point where you want it, then tune with the regular maps at that point..

 

Unfortunately the largest I can take the stock injectors too is 700.

Thanks for the how to for the cruise stuff Jack. Any tricks for dealing with AC on and AC off? Or just let the ECU make the adjustments needed. Right now I just reset the ECU again and I am driving around letting the LTFT's get some numbers so I can start to see what I need to adjust.

 

once you get it within 10% at idle and cruise, the A/C trims will also adjust somewhat accordingly, you'll still see a swing from rich to lean when the compressor cycles, but it should only affect your AFR's and shouldn't affect idle speed at that point.. Thats the reason you want the trims under 10% +/- in both idle and cruise, otherwise they will constantly adjust back and forth, and you'll have periodic trouble with drivability as it swings..